Are Plant Foods Healthful Or Harmful? A debate with Paul Saladino, M.D. and Alex Leaf, M.S.

Content By: Ari Whitten
In this episode, I am hosting a debate between Paul Saladino M.D and Alex Leaf on whether plant foods are healthful or harmful. About our guests:  Dr. Saladino is the author of The Carnivore Code: Unlocking the Secrets to Optimal Health by Returning to Our Ancestral Diet. He’s regarded as a leading authority on the science and application of the carnivore diet. Alex is a certified sports nutritionist. He’s a nutrition researcher, and he has a Master’s in Science and Nutrition.

In this podcast, Alex and Dr. Saladino will discuss

  • Their views on the biggest dietary factors that cause disease Is meat consumption compatible with good health? (They both agree on this. So if you want to see the debate portion on plant foods, skip to about 40 minutes into the episode). 
  • Can hunter-gatherer tribes teach us about the best way to eat? 
  • Different kinds of research in nutrition science, and why understanding them and their pros and cons matters. 
  • Does the evidence support that plant foods are healthful or harmful?

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Ari: Hey there. This is Ari Whitten. Welcome back to The Energy Blueprint Podcast. I am very, very excited for today’s episode. I’ve wanted to do this for a very long time. I’ve had lots of people actually asking me to do this for a very long time. I’m excited to welcome Dr. Paul Saladino to the show for what is a discussion, debate, there’s going to be some points of agreement, some points of disagreement, with also Alex Leaf, who has been on the show two or three times previously. I’ll give you their brief bios. Dr. Saladino is a medical doctor. He’s the author of The Carnivore Code: Unlocking the Secrets to Optimal Health by Returning to Our Ancestral Diet. He’s regarded as a leading authority on the science and application of the carnivore diet. Prior to medical school, he worked as a physician assistant in cardiology. He attended medical school at the University of Arizona focusing on integrative medicine and nutritional biochemistry, and he completed his residency in psychiatry at the University of Washington. Alex is, you guys have heard lots and lots of content from him. He’s a certified sports nutritionist. He’s a nutrition researcher, and he has a Master’s of Science in Nutrition. Welcome to the show, guys. Thank you so much for doing this. I know that it’s often an anxiety-provoking thing to have these kinds of discussions and debates. Thank you for having the courage to do this. I hope that we can all keep it polite and respectful, no mudslinging, or anything like that. I’m sure you guys are cool with that. I probably don’t even have to tell you, but I thought I mention it anyway. The other thing that I want to mention just before we get into it is just to try to be respectful of the other person talking and try to wait for them to complete their train of thoughts before jumping in. I’ve listened to a number of debates, especially the vegan-carnivore debates with various people or vegan-omnivore debates where there’s a lot of interruptions and a lot of mudslinging. I’m hoping we can avoid that. I also want to preface this by saying this is going to be an unusual discussion compared to a lot of the vegan-type debates that have been out there previously because they’re often focused on whether meat is harmful or not harmful. You have the vegan versus carnivore who the carnivores are saying meat is great, plants are bad, the vegan is saying plants are good, meat is bad, and there’s very little room for any overlap or consensual reality that’s being shared. I think in this podcast, there’s going to be a lot of territory that is shared and agreed upon. We’re going to focus on some specific areas that are not necessarily in agreement. I’m hoping that it’ll be a great discussion. Welcome to the show, guys. Thank you again for doing this. Alex Leaf: Yes, thanks for hosting it.

The main contributors to disease

Ari: Cool. Let’s get started I think by just stating what you think are the main nutritional contributors to disease in the western world. What do you think are the factors in the diet that are actually contributing to the high rates of disease? I think you guys both agree that there clearly are components of the diet that are major contributors to things like cardiovascular disease and neurological disease and cancer, diabetes, and obesity. I would like you each to state what you think those factors are. Paul, would you like to go first?

Paul Saladino: Sure. I think that the two biggest factors in the diet are probably processed sugars and seed oils. Seed oils being corn and canola, safflower, sunflower, soybean, grape seed, et cetera. Those would probably be the two biggest in my opinion.

Ari: Okay, that was fast. Alex?

Alex: I would argue that the primary driver of disease in the population is a diet that’s based around ultra-processed hyper-palatable foods, so combinations of refined grains, added fats, added sugars, salt, flavoring, basically, everything that’s delicious. I think that promotes the passive overconsumption of calories, which leads to gradual weight gain, especially over the holiday seasons when people tend to eat more food. Over time, it’s just like this- -giant cluster of sugar and fat and energy poisoning, so to speak, that drives the disease.

Ari: Excellent. Let’s point out the obvious, neither of you claimed that meat is a primary driver of disease. I assume this is an area of agreement from both of you that–

Alex: I would like to just state real quick. Let’s just use the US as an example. If the entire US population went on a carnivorous diet, I think that there would be a net health benefit. I think the health of most people would improve from things like reduced energy intake, increased protein intake. There might be some nutrient deficiencies because a lot of them get nutrients from the fortified refined foods they’re eating, but that could be circumvented if you give a multivitamin, just for the sake of argument. If you give a multivitamin to everyone and have them go on a carnivorous diet, I think nutrient deficiencies would be avoided and most people would improve their health.

What is the most healthful diet?

Ari: Well, let’s get back to that later. We’ll come back to that. What do you both consider to be the most healthful diet? Let’s clarify positions before we get into any points of debate or disagreement. What do you think is the optimal diet? Paul, you wrote a book saying Unlocking the Secrets to Optimal Health by Returning to our Ancestral Diet. What does that ancestral diet look like? Then, Alex, I’d like you to answer the same question, what do you think is the optimal diet for humans?

Paul: I think that it’s going to be somewhat individual and there is some nuance here. I generally feel that there are many lines of evidence, paleo, anthropological, biochemical, medical, nutrition suggesting that animal organs and meat and fat are quite nutrient-dense, contain a variety of unique nutrients that are widely health-promoting and should be at the center of a health-promoting optimal human diet.

I think that the majority of people can add some degree of plant foods to that based on their individual genetic makeup, probably their pre-existing conditions, the context that we’re working with in every individual. I think that those plant foods might be considered on a spectrum of toxicity that not all plant foods appear to be totally benign or health-promoting for all individuals, but that some individuals can eat a variety of plant foods without any apparent negative health consequences.

I think that there is a significant benefit from considering if given that seed oils, refined sugars, hyper-palatable processed foods have been eliminated from the diet and meat and organs are made the centerpiece of the human diet, I think there is a benefit to considering plants on a spectrum of toxicity. Depending on an individual’s health goals, pre-existing health conditions, often the elimination of some plant foods can be beneficial for people who are not thriving.

Ari: Alex, let me just talk for a moment. Paul, I think what you just said is perfectly reasonable. I don’t think anybody would disagree with you or maybe vegans might disagree with some of that, but I would like you to, I guess, quantify how much of the diet you think should be focused on animal foods versus plant foods. For example, I was listening this morning to one of your videos, I think just from a few months ago in maybe December 2020.

The feel of it was almost arguing that almost every type of plant food other than fruits and squashes were more toxic, were more harmful than helpful and you generally are recommending avoiding most kinds of plant foods. Is that accurate to say or would you clarify that?

Paul: Well, I would clarify that, like I did. You asked me a number of questions in that statement. You asked me what proportion of animal foods I think would be ideal for a human? I’m not sure whether you’re asking in terms of calories or weight.

Ari: You can answer however you like.

Paul: Yes, I think that generally speaking, it’s a little hard to quantify between individuals. I think that for some people perhaps, and again this is going to depend on macronutrient ratios, perhaps- -50 to 60% of the calories coming from animal foods is a good place to start but again, that depends on macronutrient ratios. If they’re eating a higher fat animal based diet then they may have more calories coming from animal foods and less coming from carbohydrates.

But I think that humans can thrive with a variety of macronutrient ratios. I don’t really subscribe to a system of belief that is focused on any particular macronutrient set of ratios. I think that, like we’re going to talk about in this podcast, the constraints are around adequate nutrient consumption. If you can get the vitamins and minerals, and I think now we’re beginning to understand that there are bioactive peptides that are valuable for humans as well that your body needs.

I think that if you can get them in a bioavailable source from a bioavailable source, and you can absorb them well, then there are degrees of flexibility to those ratios. Yes, I think that it’s not necessarily helpful to try and create rigid dogma around that.

Ari: Just a point of clarification since the title of your book is The Carnivore Code, you’re not defending a position where you’re saying the carnivore diet and all meat, basically, no plant diet is the optimal diet for humans?

Paul: No, I’m not, and I’ve never said that. Are you pigeon holing me Ari? Because we discussed that that would not go well.

Ari: I’m not.

Alex: Can I interject real quick?

Ari: Hold on Alex. Before we get into things, I want to make sure I’m allowing you guys to clarify what your positions are.

Paul: Yes, I don’t think anybody that follows me–

Ari: I’m not projecting anything on you that isn’t a position that you hold.

Paul: I appreciate that.

Ari: Okay, Alex.

Alex: Really quick. Paul, would it be fair to say that you wrote the book as a means of trying to make a carnivore diet as ideal as it could be if someone chose to follow it, but that you personally don’t believe that being completely carnivore is necessary for good health?

Paul: Yes, I think that’s a reasonable statement. I think that there were a number of reasons for writing the book. Have either of you guys read the book?

Alex: I’ve listened to a bunch of podcasts and debates that you’ve had on a bunch of your content but I haven’t read your book.

Paul: Neither of you have read the book?

Ari: I know that it’s unique in that it promotes a heavy intake of organ meats and foods that contain nutrients commonly believed to not be provided in sufficient quantities without plants. My understanding is that you basically outline how to create a nutrient dense carnivorous diet. Again, if someone were to choose to follow it, you’re saying this is probably the best way to do that. But doing something like that isn’t the same as saying this is what needs to happen, period. You’re just saying this is where I recommend you begin if you choose to go down that dietary path.

Paul: I would say that’s an accurate statement. The book begins with a consideration of human history and human trophic levels of paleoanthropology. It moves into a discussion of different types of plant toxins that could be harmful for some people based on their individual genetics and perhaps current status in terms of the health journey. Then it goes on to debunk many of the myths that are common surrounding the harms of meat.

Then at the end of the book, I have some discussion about different incarnations of equal carnivore or animal based diet, some of which include plants. Yes, there is discussion of a plant toxicity spectrum in the book. I think that the book is more than simply, if you want to do a carnivore diet, this is the best way to do it. It’s an exoneration of meat and a consideration of plants on a toxicity spectrum.

Yes, so that’s what I’m doing in the book and I think that that kind of moves us in the direction of animal based because within the general sphere of nutritional media, I think that there is a push against both of those things. There is a general push toward the idea that meat is harmful for humans or bad for the environment. At the end of the book, I discuss regenerative agriculture and the way that raising animals properly could be quite good for the environment and soil health long term and in fact, might be one of the only ways that humans will continue on the planet long term.

Also within the book, I outline this idea that I think that for many humans, optimal health will be achieved if they think about where their nutrients are coming from include more organs in their diet, include well-raised meat in their diet, and consider plants- -on a spectrum of toxicity and appreciate the fact that if someone is reading the book and is not thriving is not achieving the health goals that they want, that perhaps there is more to the conversation around plants than is discussed in the mainstream nutritional sphere, which is from what I’ve observed at a broad level, that all plants are good, the more plants you eat, the better and that if you’re not thriving, it’s because you’re not eating enough plants.

The book was meant to be a counterpoint to that, and an examination of a different way of considering the nutritional landscape. Does that make sense? Does that answer your question? I think you asked a couple of different questions Ari

Ari: Yes. Alex, do you want to say anything in response?

Alex: I think that’s a good–

Ari: You guys largely agree on this, right?

Alex: Yes, well I think that’s a good segue into what most of our discussion in this podcast will be focused on which isn’t the meat side of things, but the plant.

Ari: Before we get there, Alex–

Alex: I was going to say what mine is.

Ari: All right, go ahead.

Alex: I was going to say that, I think an omnivorous diet is the healthiest diet for human. I think that when you look at anthropological, Paleolithic and that type of evidence, I think that humans went through stages of being both herbivorous as well as primarily carnivorous with the carnivore aspect happening around 2 million years ago, around the times of Homo erectus as we started to evolve into Homo sapiens. There was a large sustenance on large like mega fauna wooly mammoth, so to speak. They supplied a lot of red, a weed digestible energy, especially with the advents of fire and making food more digestible. There were specific nutrients like DHA that they provided that allowed our brains to expand in size.

Then there was a time maybe some like 100,000 years ago where we started to incorporate more and more plant foods into our diet. We settled in where we’re at now, which is having more omnivorous anatomy. We have things that are both shorter, small intestines– oh, sorry. Shorter large intestines and colons compared to herbivores yet we still maintain things like molars for the destruction of plant leaves, that types of things. We have amylase, which has been one of the most prolific population level gene expansions that we’ve had where people develop multiple copies because it was so beneficial to what we were eating and making the most of it.

I think the ideal diets omnivorous, and I think there’s a lot of variation in terms of how much of that comes from animal products and plants. Ultimately, I do think that a significant portion of the diet should come from plant foods in order for it to be as healthy as it could possibly be. That’s basically my position. I think that a lot of beliefs around toxicity of plants, I think that they have credibility within certain niche populations like people with inflammatory bowel diseases and things of that nature.

Ultimately, I think that a lot of the claims around anti-nutrients just don’t hold up to scrutiny and I believe plants are nutrient dense sources of not just vitamins and minerals, but phytochemicals that have been shown to benefit our health above and beyond essential nutrient requirements.

Ari: Just to clarify, neither of you obviously thinks that meat is intrinsically harmful. Clearly, Paul you don’t believe that since you think meat should be very central to the diet. Alex, you also don’t think meat is intrinsically harmful and you think a fairly large, correct me if my phrasing is wrong, but a fairly large amount of animal food consumption is perfectly compatible with human health.

Alex: Yes and I think a lot of the harms of animal foods can actually be circumvented by a high intake of plant foods.

Ari: I want to just point out since we don’t have a vegan on here arguing the vegan anti-meat perspective. But there’s been various hypotheses put forth by that community and some research to support various lines of this, for example, that meat raises mTOR levels and mTOR is oncogenic, promotes cancer or IGF-1 levels or the byproducts of cooking meat, heterocyclic amines and things like that, or the compound and beef neu5gc or the TMAO hypothesis, or saturated fat and cholesterol clogging arteries. All these kinds of arguments about why animal food- -consumption is harmful. Since we don’t have a vegan on here, can each of you just make a brief statement on why you think none of those things hold water or why you think the evidence overall indicates that animal foods are either helpful or compatible with good health?

Paul: Can I just respond to what Alex said before we do that Ari?

Ari: Sure.

Paul: I just want to be clear that I’m not taking a position that humans are not omnivorous. I think that omnivory is something that’s widely misunderstood and that if you look at omnivores, the majority of omnivores specialize. They either focus the majority of their diet on animal foods or on plant foods. Over 70% of omnivores make more than 80% of their diet or 70% to 80% of their diet either plant or animal foods. There are plant-leaning omnivores and animal-leaning omnivores within the zoological collection of species on the planet.

I think that my position is that humans are probably or appear to be animal-leaning omnivore. I base that position on unique nutrients in animal foods, increased bioavailability of nutrients in animal foods, and paleoanthropology, our focus on animal foods originally, which probably had very unique facts on the growth of the brain and made us who we are as humans today as Homo sapiens. I think that that’s just a physician I wanted to clarify. Interestingly, there appeared to have been more herbivorous or plant-leaning species of hominids like Paranthropus boisei that went extinct.

Around the time of Homo erectus, Homo habilis, there’s evidence from stable isotope studies that there was a species that leaned more toward plants from the perspective of its omnivorous physiology, and that species went extinct. That’s quite interesting. I completely agree that there is evidence that 85,000, 100,000 years ago, we did swing more toward plants. I don’t think we swung to be herbivorous omnivores, but we started eating more plants in some studies, probably due to the lack of mega fauna or some would hypothesize that there was a mega fauna extinction.

From that, I suggested the hypothesis that if we look at, and I think Alex and I may disagree on this, if we look at the relative value of animals and plants in the human diet. I see animals as superior to plants and animals as the central piece of the human diet and that when humans can’t get animals, they may rely on plants more as ‘survival foods or as a ‘fallback food’. I think that that’ll be an interesting point of the conversation, whether plants are in fact fallback foods or whether they serve a unique role as a central part of the human diet.

That’s my position on plants, that generally animal foods have been consistently sought as the primary food for humans and that we do have omnivorous physiology, we can eat plants and not die. We have retained some features that are found in our herbivorous ancestors and primates, chimps and bonobos but as Alex was suggesting, there are also many adaptations to meat eating. Very small large intestine relative to primates, a longer small intestine in our acidic stomach, there’s all kinds of things.

The way we handle fatty acids, insulin resistance as a response to starvation, there are so many adaptations that really are focused on meat eating for humans. I just wanted to add that that perspective. Your question Ari was about all of these vegan arguments about the negative compounds in meat. That’s a little bit more complex than a short 45-second sound bite.

Ari: I don’t mean for you to systematically go through the evidence on each of them. What I mean is what do you feel is the most compelling evidence that has convinced you that meat is compatible with good health or is actively supportive of good health?

Paul: 2.5 million years of hominid evolution with clear evidence for a preference for meat eating. There’s anthropologic evidence and ethnographic evidence of hunter-gatherer tribes that eat a lot of meat, very healthy. Then you can look at the medical literature and if you want to go into each of those pieces, you can really make strong arguments that start to expose the fragility of those arguments, whether it’s TMAO, or neu5gc, or heterocyclic amines. There’s a large amount of evidence to suggest that those are all very difficult to defend positions based on the majority of medical literature and that makes sense evolutionarily and anthropologically.

Ari: Alex, do you want to give your thoughts on the vegan takes on meat and why you think they’re flawed?

Alex: Yes, I would say that it just comes down to logical consistency and a lot of the same arguments could be made against the vegan diet. Let’s say someone ate a diet of 100% white bread. That’s a vegan diet and it’s obviously not healthy. The same could be done with meat. It really depends on the type of meat you’re eating, how it’s processed. If someone’s going to eat the fattiest steak they can, charbroil over an open flame until it’s like black all the way through, and then eat that, you’re getting a lot of harmful toxic chemicals that are produced.

But if you do things like the Maasai, who have meat, milk, a heavy diet, they won’t even eat meat unless they coat it in some like 230 different herbs. That’s probably– they have in evolutionary learning where they realized they had less disease when they did that because we know that doing things like cooking meat when it’s coated in herbs and oils and that stuff helps reduce the formation of these chemicals.

With saturated fat, not all meat is high in saturated fat. Similarly, you could eat a diet of a bunch of coconut and you could have a super high saturated, fat vegan diet. It’s not really a good argument against meat because the meat isn’t just one homogenous group of things just like plants aren’t. There’s a lot of subdivisions. I think this type of logic can be applied to most of the arguments made.

TMAO, yes, you make it from things like carnitine, your gut, but you also get a ton of it preformed from seafood, which is consistently associated with good health outcomes in the literature. I just think there’s a lot of nuance and logical inconsistencies.

Ari: What is the evidence specifically that higher levels of meat consumption compared to let’s say a vegetarian or vegan diet is compatible with just as long of a life and as low of disease rates? Paul, I know you talk a lot about epidemiological research, healthy user bias. Can you talk about some of those studies like the epidemiological studies that have controlled for the healthy user bias in a good way, and the vegan versus omnivore studies, and why you think being omnivorous and including animal foods in the diet is no more unhelpful than a purely plant-based vegan approach?

Paul: Can I just mention something that Alex said? Alex, have you visited the Maasai?

Alex: No, I haven’t visited any of the people. All of my stuff comes from the literature that’s been published on them.

Paul: When I visited the Hadza and the Maasai I found considerations of– or much of the literature that I’d read about fiber consumption to be false or different than what I observed. Certainly, when I was with Maasai, I didn’t observe them coating it in any collection of herbs. The Hadza definitely do not do that. They just throw the baboon on the fire and then eat it. The Hadza are doing nothing to mitigate any of the compounds formed in an open fire.

I’ll tell you that the meat that I ate with Hadza was not charred. It was cooked quickly on fire and we ate the whole baboon, but there was no consideration of herbs and they weren’t going to stop and gather herbs and put it on the meat and nor that I observed that with the Maasai.

Certainly, also the Hadza did not eat a high fiber diet for the week that I was with them. Some may argue in response that I did not spend enough time with them and believe me, I would love to spend multiple years with the Hadza, but they did not eat a high fiber diet when I was with them either. Many of these conceptualizations of what these groups do, at least a few of them, I have found to be inconsistent when I’ve gone there in person. Your other question Ari, what was it about?

How healthy user bias influence science

Ari: I would love for you to talk about the healthy user bias and epidemiological research more broadly, and why you feel some of the epidemiological research that has controlled for those confounding variables in the vegan versus omnivore studies have definitively shown that animal food consumption, omnivory is no less healthy than veganism.

Paul: There’s nothing definitive about observational research in general. You must remove that word. There’s a pretty clear signal in the research that when you control– If you compare, for instance, like the UK shoppers study is a great study, if you look at the overall death rates of vegans versus omnivores, vegans have a lower death rate. But if you then control in the omnivory group, for those who have healthy behaviors, which I think starts to get at the healthy user bias, or at least the unhealthy user bias, you see that the death rates are exactly the same.

The assertion or the inference or the hypothesis that you could draw from that is that the benefits of a vegan diet that we see in observational epidemiology are unlikely to be linked to the absence of meat in the human diet and more likely to be linked to many of the companion behaviors that come along with that sort of a food choice. Most listening to this will understand that in the West, we’ve had a paradigm or at least a set of information coming from nutritional authorities for 70 years since Ancel Keys that meat is harmful to humans.

There is an association in our behaviors of those who shun meat or eat less meat and those who do more ‘healthy behaviors’ like being in the sun, exercising, getting colonoscopies and mammograms and they tend to be of a higher socioeconomic status. This is what we call the healthy user bias that there is an association there. That comes up repeatedly in studies that are done in the West. Now intriguingly, when we do studies that are observational epidemiology in the East across Thailand, Singapore, China, other countries, we don’t see the same thing and we see a very different trend.

In my discussions with plant-based advocates who love to rely heavily on observational epidemiology, because that is one of the only positions that they can take. They really don’t have much answer for the counterpoint that if you look at these large studies done in Asia with 200,000 to 300,000 people over four to eight years, you find a very different association. You find that the men who eat the most meat have the lowest rates of heart disease and the women who eat the most meat, have the lowest rates of cancer.

When we see these conflicts, we have to ask ourselves questions about whether this epidemiology, this correlation is actually telling us what we think it’s telling us. That’s why it’s so misleading. You’ll never see this reported in the mainstream media in the West but if you dig into it, there’s quite a lot of inconsistency here that needs to be examined. Again, the overarching framework for this is that observational epidemiology in my opinion, that’s a very poor thing to base your nutritional decisions on. It’s a very shaky set of data to make decisions about human health because of these confounding biases, healthy user bias, and then unhealthy user bias.

Unhealthy user bias is the opposite of healthy user bias. If you think about the paradigm or the narrative for the last seven years, those who have eaten meat are generally the people who are rebellious and are saying, “I’m going to ride my motorcycle and smoke my cigarettes and drink my alcohol and eat my hamburger at McDonald’s with a bun with seed oils, drenched fries, with milkshake, hyper-palatable processed foods.”

These are the key concepts I think that lead to a lot of misunderstanding around this observational research. I’ve said in my social media, or asked the question, how often do you see someone go to McDonald’s and just order hamburger patties? Or how often do you go to a barbecue in the Midwest of the United States and see people just eat steak without a brownie, a beer, hyper-palatable processed food with processed sugar and seed oils? These are the correlations, or these are the associations that observational epidemiology cannot distinguish between.

Ari: Just for me to add one point before you jump in here, Alex. In listening to the conversation with Dr. Fuhrman, basically, this was the crux of your disagreement. Is Joel Fuhrman was basically saying, “Here’s all these thousands of epidemiological studies that clearly show that more meat consumption is harmful and higher plant food consumption, fruits, and vegetable consumption, nuts, and seed consumption, beans and so on are healthful.”

You were basically saying, “I think all of that research for the most part is nonsense, is garbage and we should not be looking to that as the gold standard.” There was basically an impasse as far as your ability to agree on what type of science we should even be looking at to determine how we should eat.

Paul: I believe that I drew an analogy to a landfill- -with that research saying that if the research is low quality that, that you can stack more and more low-quality research upon itself, that doesn’t increase the quality of the research. I think that I would bristle at anyone– I don’t think that it’s completely garbage. There’s an association there from which we can draw a hypothesis, which needs to be tested. But that it’s low-quality research that we should not base decisions on, especially when we have interventional research with red meat that suggests the opposite, when we have human evolution, which is clearly a path taken with a lot of meat and organ consumption, and when we have conflicting epidemiology done in places with a different narrative surrounding it.

That was my general discussion with Joel Fuhrman. On that podcast, he claimed that there were interventional studies with unprocessed red meat showing harm in humans. He’s failed to provide any of those. In response to me, he just sent an email with six more epidemiology studies. He just doesn’t quite understand that it’s very difficult to control for these biases in research and we should be looking at interventional research as the gold standard.

Ari: Alex, I want you to jump in with your thoughts in all this. I want to just interject one more point, which is the hierarchy of scientific evidence just to help listeners understand that there are levels of evidence that are considered stronger or weaker evidence. I think it’s accurate to say what Paul just said around epidemiological evidence being used to formulate hypotheses, which need to be tested in more controlled experimental studies.

One of the challenges as I see it from my perspective is I do think there’s some legitimacy to Joel Fuhrman’s claim that there is value to long-term research to see how things actually play out in the end as far as mortality outcomes. It’s really hard to do that in the context of a randomized controlled trial. Anything that lasts more than a few years tends to cost many millions or tens of millions of dollars to do and it’s just very rare to see any kind of really long-term interventional study.

I think there’s a bit, there’s a bit of a challenge just around like how we value different types of science on this and which one we consider to be strong or weak evidence. Alex, I know, you know, a lot about this topic as well, so I’ll let you jump in here.

Paul: Can I respond to that Ari?

Ari: Sure, please.

Alex: Go for it.

Paul: I’m just saying that there’s plenty of long-term evidence in Asia that shows that meat is associated with better outcomes. I don’t know how Joel ignores those.

Ari: I think the argument that I’ve seen, like, for example, from David Katz on that subject, I read a bit about that is poverty is a huge factor that influences those epidemiological studies. The people who eat less meat in those cultures generally are poor and generally eat like mostly white rice. That was the argument that I’ve seen David Katz make on that subject.

Paul: He’s talking about inherent bias, which is exactly what we find in the United States.

Ari: There’s a healthy user bias factor as you explained earlier, but then there’s also this, especially in I think the poor Asian countries, there’s a poverty socioeconomic factor that plays into the results of those epidemiological studies as well.

Paul: Of course. Basically, they’re highlighting the fact these studies are often extremely biased and that it’s very difficult to sort this out. I don’t think that invalidates any of these arguments. To me, it’s just like, yes, this is landfill. This is not what we should be basing things on. If we hope for a long-term study, then we just might not get this because it’s going to be very, very difficult to control for these variables and yes I mean, there’s bias everywhere. The same could be said in the United States.

Ari: Got it. Okay, so Alex, Paul and I have been chatting here back and forth a bit. I want to give you an opportunity to chime in on all this.

Alex: I think looking at meat might be the wrong thing especially for this discussion because there’s intervention studies showing that introducing even lean red meat into people’s diets, for example, doesn’t affect blood lipids. It doesn’t affect common risk factors. There’s a strong argument to be made about including meat for protein adequacy and nutrient adequacy, especially in like developing countries where they don’t eat a lot of meat because of that poverty factor and they actually suffer things like growth stunting during childhood. Trying to give them meat solves the issue by supplying zinc and protein and other nutrients they need to overcome those issues. Instead, I would like to look at plants. I’m not aware of a single intervention or observational study that actually shows a detriment from eating more plant foods. From my knowledge, the studies show that there’s either benefits or just no benefit or detriment at all, they’re benign. In other words, you either have a neutral outcome or a beneficial outcome, which makes me question. If we’re looking at an optimal health diet, let’s just say that meat is healthy just for the sake of argument, that’s common ground. I think that there should be some animal product in the diet, but how much should now be plants?

I think that the overwhelming data shows that the more plants you eat, the better the outcomes. In fact, there was just a meta-analysis published in 2020 in the Journal of the American Heart Association showing that when you look at 5 million adults from 81 different studies, every 200 grams of fruit, vegetable, or their combination in the diet has a 3% to 15% risk reduction in developing heart disease, cancer, dying from any cause, suffering a stroke, and there’s no apparent plateau. In other words, as they continue to go all the way up to like 800 grams per day, the relative risk continues to decline.

Then you have all these interventions of plant-heavy diet, like the DASH diet, Mediterranean diet, even vegan and vegetarian diets. You put people on these interventions and their health improves. Even the Paleo diet, every Paleo diet includes a good serving of plant foods, even if it excludes grains and dairy, and what else, legumes. They still include fibrous vegetables and fruits, and you see health benefits. I’m personally curious to whether Paul has come across any studies that show that adding plants into someone’s diet has had a detrimental outcome.

Ari: Unrefined plants, right?

Alex: Yes, unrefined whole plants. I’m not talking about whole grains, either. I don’t care about those, take them or leave them. I’m talking about, fibrous vegetables and fruits. Then before —

Ari: A similar question to the one you posed Paul to Joel Fuhrman on interventional studies around meat, adding meat, and can you find one that shows a harmful outcome? Alex is asking you, are you aware of any studies where they’ve added unrefined plant foods to the diet and shown harm?

Paul: Yes.

Ari: Which then? Can you explain?

Are plant foods healthful or harmful? The problem with many interventional studies

Paul: This is a study from 2002. They were trying to include catechins in the diet from green tea extract. In order to do that, it’s a small study, eight smokers, eight non-smokers. In order to do that they had one of the groups go on a flavonoid free diet because they wanted to study the effects of this one catechin from green tea and—

Ari: I just want to quickly point out, so the question was unrefined plants and this is an extractive of green tea so [crosstalk]

Paul: Yes, if you hadn’t interrupted me I was going to tell you the answer here. There were no effects to the green tea extract intervention, and as you can see here in the conclusion, since no long-term effects of green tea extract were observed, the study essentially serve as a fruit and vegetables depletion study. The overall effect of the 10-week period without dietary fruit and vegetables was a decrease in oxidative damage to DNA, low proteins, plasma lipids, and concomitantly with marked changes in antioxidant defense. If you read the paper, the changes in antioxidant defense were in a positive direction.

This is one study that found, again, every group is individual and in these people, when they eliminated flavonoid containing fruits and vegetables for 10 weeks, at least these surrogate outcomes looked to be better. Now, the other thing I’ll say is that there are many studies that fail to show a benefit to fruit and vegetables when they are included in the human diet.

If we are looking at these interventional studies with fruit and vegetables, there’s a large meta-analysis that has been done looking at interventions. People often ignore the fact that there is a large number of studies or a moderate at least number of studies that satisfy this criteria. This isn’t exactly what Alex is asking, but

they don’t improve, the outcomes is what I’m saying. Increasing the vegetable intake dose is associated with a rise in plasma carotenoids without modifying oxidative stress or inflammation in overweight or obese postmenopausal women. There’s multiple studies like this. I’ll show a few more. This one is [unintelligible 00:45:25] [crosstalk]

Alex: I have looked at that all of those actually. I have one, two, three, four, five, I have six studies here that all show that same thing, that adding in 600 grams, so like a pound and a half of vegetables to the diet, doesn’t modify primarily markers of oxidative stress towards DNA and things like DNA strand breaks.

My issue with these studies is that when you look at the interventions, they consist mostly of using lettuce, carrots, tomato and orange juice and they’re also looking at one very specific outcome. I have no problem saying, “Hey, adding fruits and vegetables may not reduce the amount of DNA damage you experience.” That’s fine, but that’s just one outcome and I think that that’s a narrow field of view when you look at all the things that impact health.

We have to also look at things like, “What about endothelial function?” We have studies showing that adding in just a half-pound of spinach for one week into someone’s diet improves endothelial function by several percent and then you have other markers such as visual health. We have studies that show that getting people to eat spinach, because of the lutein it provides, improves visual function, reduces the risk of macular degeneration. There’s like some 10 studies that getting people to eat blueberries and it improves cognitive function and reduces the progression of Alzheimer’s disease because of the anthocyanins that they’re providing.

I think that when it comes to interventions, there’s a lot of interventions that use whole plant foods and show benefits and I think there’s a lot that also don’t show benefits. I think it depends on the outcome you look at, but I haven’t necessarily seen any that add plant foods into someone’s diet that show harm. It’s either a benefit or a neutrality.

I know that you shared the study that showed using a flavonoid-depleted diet improved markers of oxidative stress and that’s interesting. I haven’t read that study personally. The first question though that comes to mind is how did their diet change? Like they had to stop eating flavonoid-rich fruits and vegetables, but flavonoids are just one component of polyphenols. What did they replace those with?

Ari: Well, I have a broader question, which is–

Paul: Ari, I’d prefer if you don’t– Please allow me to respond to Alex before you shift the conversation.

Ari: Go ahead, Paul.

Paul: Okay, thank you. If you look at that study that I just showed, Alex, I’ll screen share it again, they did not use lettuce, they use broccoli which most people would say is one of the most healthy things. The fruit and vegetable group, initially 600 grams of vegetables containing apples, pears, orange juice, broccoli, carrots, onion, and canned tomato.

You can look at these studies, most of them include some sort of a vegetable that many would consider it to be a ‘superfood’ though I would disagree with that designation. They have Jerusalem artichokes and things like that. I’m going to gently disagree with your assertion that they’re including weak vegetables because I don’t know what you would consider to be good for humans but they’re generally including things that most people would consider to be healthy for humans.

Endothelial function is very difficult to measure. I’m not sure if you’re discussing something with a post arterial dilatation, that’s really poor measure of endothelial function, in general, we can’t really use. That’s just a bad measure, I think a bad metric to use that sort of a measure of endothelial function. Though I agree endothelial function is critically important and there are many compounds in meat that you can make the same argument might contribute to improving endothelial function by contributing to nitric oxide production and endothelial nitric oxide synthase precursors like arginine and et cetera.

Going on from that, I think it’s important to consider that the lutein studies of macular degeneration are– I’m not totally excited about those studies. I think that if you really look into macular degeneration, I’ve spoken to an ophthalmologist, Chris Knobbe, on my podcast about this a lot, that I’m just not convinced by those studies. We can go through them individually if you’d like, but that takes us down quite a rabbit hole. I think they’re pretty weak in their data, that this lutein in these vegetables is magical.

Now, if we pull back for one moment, I think we get to an interesting point which is to my overarching assertion that I don’t really believe that plants have, or I should say the plant– I do believe that plants exist in the toxicity spectrum. I haven’t really talked about what I believe that to be, that’s something I can discuss as well. I think that when you look at plants, it’s very important to consider the fact that I’m taking a position where I don’t believe that many of these leaves, roots, stems, and seeds contain compounds that are unique or unique in their benefits for humans. I think that they may contain compounds that have biological activity in humans and also other compounds that have negative effects in humans.

As I mentioned earlier, the position that I take is that I think that we could get many of the benefits of eating these compounds by eating meat which actually contains many of these compounds with perhaps less of the defense chemicals. I think that when we’re looking at these interventional studies, we get granular and we can look at this study or that study, but it’s pretty hard to ignore. This goes to anecdote the fact that many people improve when they cut these things out of their diet, and that’s not a very strong position to take but you observe it clinically over and over, and it’s very hard.

You could look at hundreds to thousands of case reports of people excluding certain plant foods in their diet and seeing improvements, whether it’s oxalate nephropathy from green smoothies, that’s a case report document, whether it’s other nephropathy from oxalates and Chaga mushrooms, whether it’s case reports about elimination of plants leading to improvements in inflammatory bowel disease. I think what we need are better design studies to sort this out because at the case report level, there are many examples of people improving when they cut roots, stems, seeds, and the leaves out of their diet which I think of as the most toxic parts of plants.

The corollary question then becomes, is there a downside to doing that? I don’t believe there is. I think we can get anything that would be beneficial in those plants, from eating meat and organs including phytochemicals. We can move on to the fiber discussion whenever you want but I don’t think humans need massive amounts of fiber to be healthy. Hopefully, that helps clarify that position.

The blueberry studies specifically are pretty underwhelming. We can look at them but if you look at the standard deviations and the standard errors of the mean, they’re not impressive. Blueberries don’t cure Alzheimer’s, is what I want to make a point about. They certainly don’t cure neurologic degeneration. I can pull one up if you’d like to see. Some of these studies are pretty, they’re just not incredibly convincing in the amount of change in people when they include these foods in their diet.

Ari: I’d like to interject a couple of things and add to this.

Alex: Ari, real quick. I just want to respond by that to kind of get back to the central point which is that I spit out several examples and each one of those examples, Paul, you just said the results were underwhelming and that’s fine. The results can be underwhelming. They were more than examples of things that show that adding plant foods into the diet have certain benefits. I haven’t yet had you answer the question of a study that adds plants into someone’s diet and shows negative health benefits. You have shared a study that shows that markers of oxidate of DNA oxidative stress improve when someone limits specifically flavonoid-containing fruits and vegetables.

Paul: It was all fruits and vegetables really. It wasn’t just flavonoid. We can go back to that study and look at it. Basically, like I said, Ari, please let me finish.

Ari: No, Alex has been quiet. You’ve talked a lot, Paul, let’s give him a chance to fully elucidate.

Paul: Sure.

Alex: That’s fine. When they alleviate all– but that goes back to the other point I made which is that we have a lot of different health markers to look at. The same arguments can be made about meat. Frankly, where you could show a study where it says, “Hey, adding meat into the diet doesn’t seem to affect LDL cholesterol.” Like just as one example. “I’m aware of a med analysis that shows that. Intervention studies, it doesn’t affect one of these primary cardiovascular outcomes,” but then there might be another study that then uses, for example, fatty meat that does show that outcome one compared to something like cheese where the milk fat globule membrane is present, and it all comes down to context and everything.

My central point is that you have data showing interventions of using specific fruits and vegetables have certain benefits even though the magnitude of that benefit might is variable and oftentimes weak. Where is the data that introducing fruits and vegetables into someone’s diet or changing someone to a diet that is rich in plants, such as the Mediterranean diet, or even the Paleo diet, that that has a harmful effect rather than a beneficial or neutral effect?

Ari: Go ahead, Paul.

Paul: I think that is mainly in case studies at this point, and that there are not studies that have been designed to look at that. I don’t think we have studies that disprove that notion but I suspect that because of the way we have thought about plants. I think that this is something that is difficult to debate. They’ve gotten a free pass over the last 70 to 100 years. The assumption has been that plants are benign and healthful. We don’t really have studies that have been designed to study that. There are no studies that have tried that and failed. There just aren’t studies that are organized like that.

It would be very difficult to get funding to say, “Hey, we’re going to take one group and they’re going to eat an animal-based diet of meat and organs and the least toxic plant foods. We’re going to have another group and we’re going to give them meat and organs and tons of kale.” That type of study has not been done. That’s a very difficult thing because I think that that’s a hard thing to get funding for and a hard thing to get past a board or just actually get people interested in doing. Hopefully, it will be done in the future.

Do plants cause goiters?

I think that there are mechanistic studies that suggest potential harm from these plants. That is generally what we look at. We couple that, or I would couple that ideologically with multiple case reports of harm or chronic illnesses improving when these things are removed. Now, I think that we can use the example of chronic goiter here as an illustration. There’s no study that I’m aware of where people eat more cassava but you have only to look at endemic goiter in Africa to people who include more cassava in their diet which is often iodine deficient because they’re not eating a lot of animal foods, and they have the worst outcomes.

Similarly, maybe they have hugely hypertrophied thyroid glands and massive hypothyroidism from inadequate iodine absorption to the level of the thyroid due to the isothiocyanates in casava. I think that exclusive studies of vegan vegetarian diets showing profound nutrient deficiencies are not perfect but they do show that when lots of plants are included in the diet, of course, this is in the context of the absence of meat, people run into major issues.

Ari: Is that an issue with the plants or with a lack of meat?

Alex: Well, it could be both. There’s one study that I actually will point to. I can probably pull it up in which people were given oysters, and you can see the blood levels of zinc rise when they’re given oysters, but if those oysters are administered with plant foods like tortillas or beans, which are high in oxalates and phytic acid, the elevation of the zinc levels postprandially is essentially completely abrogated. I think that that’s a specific example of the phenomenon that I’m describing here, that plant foods are not uniquely benign for humans and that they do contain anti-nutrients. It just depends on inhibitors in many cases, and that the inclusion of these can affect things negatively.

You bring up a good point that we do need more controlled studies. I would love to see that. It just hasn’t been done. Mechanistically, I think there’s a wealth of information to suggest how this could be harmful and there are real-life examples of overconsumption of certain plants leading to major problems with humans, cassava being a great example with this endemic goiter.

Ari: Hold on one second, Alex, I want to just interject a bit of context and I’m glad we’re in the cracks of the debate here around plant foods being helpful or harmful. One thing that I think is worth pointing out is just the concept of it is possible to find some study somewhere showing almost anything. When we talk about anecdotes too, it’s possible to support any way of eating based on that.

You can find people who have eaten raw fruitarian, raw vegan diets, or entirely fruitarian diets who swear transformed their health. You can find people who ate raw meat diets, you can find people who have eaten a potato diet, in fact, there’s books written on the potato diet, eating nothing but potatoes for long periods of time and you can show biomarkers showing it decreases– it improves weight loss and insulin resistance and various biomarkers related to inflammation and so on.

I don’t and I think you guys would agree with me that find that to be a compelling line of evidence that eating only potatoes is the ideal human diet. I think we need to, in the context of this hierarchy of evidence, be willing to also talk about what the weight of the evidence indicates. So for example, when citing studies, looking at more or less vegetable consumption and oxidative stress or markers of inflammation, you could probably find 1 or 5 or 10 studies showing that it wasn’t linked with improvements in oxidative stress but there are certainly at least hundreds that have the opposite finding of interventional studies. We have to be willing to consider what is the weight of the evidence in this discussion?

Paul: I disagree with you there, Ari and if you are going to also be a part of the debate, if it’s going to be one versus two, then you must allow me time to respond to both of you.

Ari: I’m presenting what I think too and I would love to get [unintelligible 01:01:20]

Paul: A moderator is not supposed to do that and before the debate, it was not discussed that you would be showing your own opinions. So I will express this [crosstalk] that you were meant to be a moderator rather than another person. If I’m debating two people, that’s fine.

Ari: No, I think I’m doing a good job with that. Let me be clear about my bias. I don’t think meat is harmful. I do think plants are helpful. I’m supportive of omnivory but I also think that from my opinion, the weight of the evidence and the hierarchy of evidence should be considered when asking questions of science. So please feel free to respond if you disagree.

Paul: I think that this is a very slippery slope. When you consider the weight of the evidence, you must consider the quality of the evidence and that becomes a quite involved discussion. Again, I’ll just reiterate that I’m happy to do that. It’s just a different thing. If we’re going to discuss the actual studies that are looking at fruit and vegetable inclusion in the human diet, we should go study by stud.

We can do that if you want. I can pull up the fruit and vegetables meta-analysis looking at these studies and we can look at these studies individually, but I think that looking at the weight of the evidence is a fool’s errand. You should consider the quality of the studies as well because the individual interventions that are done just because more studies [crosstalk]

Ari: [inaudible] in the hierarchy of evidence.

Paul: Not from what you were saying, you were saying the weight of the evidence should [crosstalk]

Ari: No, the hierarchy [unintelligible] and specifically talks about interventional studies being higher quality, meta-analysis and systematic reviews of randomized controlled studies being the gold standard.

Paul: That’s not what I’m referring to. If you were listening to me, I was saying that if we’re going to compare a variety of interventional studies, we need to look at the interventional studies individually and if that’s something that we’re going to do then we have to do that. If you look at the interventional studies that are done with fruit and vegetables, then we can do that.

I’m not aware of any studies that are interventional with kale. If anyone is familiar with my work or has read my book, they will know that I consider fruit to be less toxic than seeds, nuts, grains, legumes, stems, and leaves.

I’m not going to take a huge issue with fruit inclusion studies in the human diet but I am going to take an issue or I think that humans will do best by being aware of the fact that stems and leaves and roots and seeds do have defense chemicals that’s very difficult to debate and that the blanket consideration of them as universally benign for humans, I think needs to be reconsidered because these defense chemicals do appear to be harmful for some people. I don’t see a reason to include these foods in the human diet when you can get many of the phytochemicals in other places or many of the benefits from meat and organs.

If we’re going to go tit for tat and look at the interventional studies with fruit and vegetables, we will need to pull up the meta-analysis with these and look at them individually. I think that it’s a very unfortunate position to say or to say, “Well, there are more studies looking at this and showing this finding,” than to actually appreciate the quality of those individual studies and what we’re actually discussing at a more granular level. So that’s why I would disagree with you from that perspective, that’s the position that [crosstalk]

Ari: [unintelligible] reduces systematic reviews, take the quality of the interventions into account when they do those [crosstalk]

Paul: No, they don’t. No, generally they’re not. It’s a little bit more of a nuanced discussion if we’re talking about it now that if you look at many of these studies, we have to divide it into, and this might be an interesting discussion. I think it would be fairly esoteric for most people to listen to. If you look at many of these studies, are we going to consider studies of people who are chronically diseased? Are we only going to look at studies that increase the ‘vegetable’ but not the fruit intake of otherwise healthy humans? Because those are very different populations.

It’s one thing to take a diseased individual who probably has a compromised oxidative stress status, metabolic health and include a polyphenol and say, “Look, in this person with underlying disease,” whether it’s diabetes, metabolic syndrome, many of these studies are done on people who have underlying chronic illness. We can include this food and see an improvement in the oxidative stress. That’s a very different situation than going and looking at healthy individuals. That’s why I think that so many of these counterstudies that don’t show a benefit are important to consider, that many of them are done in healthy individuals and there’s no real benefit to including these plants in the diet.

We have to appreciate, and this is Alex’s earlier point, that in most of these studies, they’re only looking at oxidative stress markers, DNA double-strand breaks, things like this. They’re not looking at other markers that might give us an indication of how these vegetables, specifically roots, stems, leaves, and seeds, could be harmful for them. They’re not looking at overall micronutrient status. They’re not looking at thyroid status. They’re not looking at overall iodine incorporation for the thyroid for instance. They’re not looking at male hormones. Many of the compounds in these foods could act as xenoestrogens.

The problem is that these studies are built to look at certain metrics. Of course, nobody’s going to do a perfect study, but if we’re not looking at metrics where there could be harm, again, we don’t know what’s going on there and mechanistically, there are studies to suggest that these plant foods, because they are defended, because of their position within ecosystems, could be harming humans. Then, the follow-up question that I continue to ask is why would we include them in the human diet if we can get all of the benefits and more by selecting more ideal foods for humans.

Ari: Okay, Alex, go.

Are fruits healthful or harmful?

Alex: For a point of clarification because he brought up fruit, and given what you’re bringing up as the harmful, I guess we could call them anti-nutrients, is their common nomenclature, would you say that phytochemicals are beneficial or harmful or benign just in general? For example, fruit. Blueberries provide anthocyanins. Would you say that those have a net benefit? Or mango provides mangosteen, apple provides ursolic acid. Would you say that these things are either benign, AKA, they don’t hurt us, or beneficial for humans and that you would be okay with their consumption because they are present in fruit?

Paul: I think that you would have to look at the literature for each of those and go down the rabbit holes. Ari and I had a conversation offline when we were in Nosara about anthocyanidins. I need to review the literature on that. The last time I looked, I wasn’t particularly impressed by the benefits of that family of compounds. I do think like philosophically what I can imagine, and I think that sometimes with nutritional science, we have to make this hypothesis because it’s difficult to study, that human certainly would have consumed this and we would have sought it out. It’s brightly colored, it’s on trees.

My suspicion, or at least my hypothesis, would be that some of these phytochemicals found in fruit may be benign or maybe we’ve evolved more of a position to be able to detoxify them or to deal with them because I think that we would have had more consumption of them evolutionarily. Of course, this is just my conjecture and my own opinion that people could disagree with, and it’s difficult to support it scientifically other than ethnography or paleoanthropology, but there are mechanistic explanations there.

Without going down the rabbit hole of every single compound that you mentioned, I couldn’t say, I know that anecdotally when I eat mangoes, I get an allergic reaction to my mouth probably from the urushiol in the skin of the mango. I don’t eat mangoes even though I’m in Costa Rica. I don’t believe that a mango is going to contribute to good health for me personally because clearly I [crosstalk]

Ari: When I was with you two weeks ago, you were eating mango.

Paul: Yes, and I had a reaction on my lips from that. I think that it’s very individual and that fruit doesn’t seem to do well with me. I would imagine if the oils are irritating my lips, that perhaps they’re irritating my digestive tract or causing other issues. That’s a fruit that I don’t personally include. As I said from the beginning I think there’s a lot of individuality and it’s important to consider that these plants may not always work well for every human.

I’m willing to consider that there are compounds in fruit that may be benign or that may be dealt with by humans. Maybe some of them are even beneficial for humans. I’m most interested in the more toxic parts of plants. Again, it’s a construct that I would imagine based on the way plants exist within an ecosystem.

How plant compounds end up in meat

As I mentioned, one of the things to also consider, and this is something that I saw recently that I thought was quite fascinating and I’ll show the paper briefly, is the fact that there are, and there certainly are plant compounds that end up in meat and organs. This is another wrinkle in the story. I think that it’s quite fascinating to imagine that animals may take in plants and detoxify some things and then place other things in their meat.

I think that, from my perspective, when I see this, I think, “Well, here is more evidence that plants may not be such an indispensable part of the diet, and if these compounds are health-promoting or even benign, we can even get exposure to them when eating meat and organs.” I see this as a much more or as a safer way to get these compounds than eating them in the plant food source that may have lots of other anti-nutrients in its native state not having been processed by the animals.

You can see the studies that we’re viewing here in this paper. It’s quite an interesting study by Fred Provenza and some other people. This point of the study is just that, I’ll read the title for people who are listening, ‘Health-promoting Phytonutrients are Higher in Grass-fed Meat and Milk Versus Factory-farmed Animals.’ Again, just so the point is clear, I think that this is quite an interesting wrinkle to consider that maybe if we consider, if we think, or we believe that these phytochemicals have unique benefit versus being just benign in humans, there may be better ways to get them than eating them in defendant plants in nature that are actually trying to survive. Maybe we let the animals take care of them. Just an offshoot idea but I think it’s relevant.

Ari: The reason you think it’s better in that context is because of the lack of other compounds in the plants?

Paul: Yes. That they would be interesting to look at this meat with grass-fed meat versus grain-fed meat or just meat in general and see the sulforaphane end up in meat or is the animal going to use phase II detoxification so much that it actually removes this one chemical and then this one ends up in meat. It’s just an interesting line of thinking.

Ari: Alex, [unintelligible]

Alex: Another example of that is lutein which is present in egg yolks, especially if the eggs are fed marigold flowers, and it’s far more bioavailable than spinach. I completely agree that we can obtain certain phytochemicals from animal foods in oftentimes higher quantities and bioavailability than the plant foods themselves. For us to even care about that, we would have to admit that phytochemicals have health benefits and that their inclusion in the diet would have in that benefit.

Yes, I agree with you, I think it comes down to an individual basis. Obviously, we’re not going to go through every single one of the tens of thousands of phytochemicals that have ever been identified now. Humans have definitely evolved ways to incorporate those phytochemicals into their physiology for net benefits. Again, lutein is absolutely essential for protecting the retina from oxidative stress and blue light. It’s also the primary carotenoid along with, oh God if I can remember the name, beta-cryptoxanthin within the brain to prevent DHA oxidation and we get these primarily through plants. Throughout evolution, yes, we ate eggs, but they were not a dietary staple.

Similarly, every single carotenoid that we know of, including astaxanthin, beta-carotene, lycopene, as well as lutein and zeaxanthin have been shown to be readily incorporated into our skin to protect against UV induced DNA damage within the skin which is proposed to be an evolutionary adaptation that took advantage of our diet in order to prevent the destruction of full light, in order to minimize the risk of skin cancer because they basically minimize the amount of damage our skin takes. Even though I think that evolutionary arguments for what diet is ideal are biased because they’re based around what we needed to survive and reproduce, not long-term health, I do think that using that same logic, we could make an argument that phytochemicals, or at least some phytochemicals, that are not just beneficial for physiology, but actually necessary.

Ari: I would like to touch on anti-nutrients. I would like to touch on fiber and if you guys have any concluding thoughts on phytochemicals, feel free to jump in before we get into anti-nutrients and fiber, and then I would like you each both to give what you feel, I guess, is the most compelling argument for why either we should lower the amount of plants in our diet, or have more plants in our diet. If you have any thoughts on phytochemicals, feel free to jump in guys, and then we’ll go fiber and anti-nutrients.

Paul: Can I just respond to what you were saying, Alex I don’t know if you were finished.

Alex: No, yes, go for it.

Paul: I think that lutein is actually found in animal fat as well. I could find the paper but I believe that lutein is found in [unintelligible] and tallow and animal fat. To your point, I think that it’s very interesting to imagine that even when we were not eating a lot of plants evolutionarily, we might’ve gotten exposed to these ‘phytochemicals’. I certainly will not take the position that these phytochemicals are always bad. I do think that there are clear examples of phytochemicals that can be harmful to humans and so it bears more consideration to understand why cassava in Africa is so dangerous with isothiocyanate and yet some phytochemicals appear to have benefits for humans and many of them we will get through meat and organs, liver, fat, things like this which is quite fascinating to me.

How certain foods when eaten in excess may cause harm

As I said earlier, I think that that really brings up this quite intriguing possibility that eating more meat and organs and fat might be a safer way to even get these if we consider them to be healthy. You mentioned the skin which I want to touch on because I think it’s quite an interesting example of what’s going on here as well. You mentioned that many of these carotenoids end up in the skin and are beneficial and I thought it was– it’s fascinating to see that there are also compounds from plants that can end up in the skin and be harmful like psoralens. I’m sure you’re familiar with these.

Alex: [unintelligible] psoralens?

Paul: Psoralens.

Alex: I’ve never heard of that.

Paul: Psoralens are in things like celery. This is a dermatologic journal from 1992, severe phototoxic burn from psoralens ingestion. Psoralens are pretty widely studied and basically, this is a response saying that because this person was eating a pound of celery root, it contained 22.5 milligrams of psoralens and referencing– That’s not out of the realm of possibility if you make a celery root, like a mashed celery root for Thanksgiving, and people go ham on the celery root, but it was associated–

Alex: Somebody could have that as a staple for sure.

Paul: Yes, it was associated with burns and this compound, these compound, this psoralens, P-S-O-R-A-L-E-N S, they’re known to be photosynthesizing at least in some individuals. It’s tricky to sort this out and understand where these are coming from and I think that even within this discussion, I’m thinking more and more like maybe we would have to differentiate like is there a possibility that these phytochemicals coming from certain parts of the plant might be more harmful to humans than phytochemicals coming from fruit? This is just based on an evolutionary hypothesis, stemming from which things we may have eaten more consistently over the course of our progression as humans and hominids. I just wanted to highlight that idea about psoralens and negative effects from those in excess. That’s pretty well-documented in the literature.

Ari: Well, I just want to comment on pleasantly surprised to see how much you guys are both very reasonable in responding to each other and acknowledging the areas of agreement. I applaud you both for that and for the politeness and lack of mudslinging. You guys want to jump to fiber or anti-nutrients first.

Alex: I would rather do anti-nutrients. Fiber could be, frankly, an entire discussion and I think anti-nutrients are more central to the argument of Paul for why we should not have a significant portion of our diet come from plants. I think that that would be more important to touch on and I’ll really let Paul start. There’s several anti-nutrients so I would like if Paul were to pick one, basically as an example, and then we can start with that one and maybe move on to a couple more depending on time constraints.

Ari: Just so we’re clear, we’re talking about things for the listeners like lectins, oxalates, phytates.

Alex: Goitrogens, phytoestrogens, tannins.

Ari: Paul, I know you touched on this a bit earlier as far as inhibiting zinc absorption, but feel free to give your overall take on these kinds of anti-nutrients.

Paul: It is interesting to think about these. There’s a variety. Some of them are polyphenolics, some of them are not. Isothiocyanates, for instance, are a different family of molecules than polyphenolic molecules but when you look at them, there is a question. As Alex said in the beginning, the question is, is the consideration of these overemphasized or do they actually present a problem for human health?

From my perspective, there is a significant amount of literature to suggest mechanistically how they could be harmful to humans. Like I said, there are a number of case reports. I don’t know, maybe we’ll do isothiocyanates. Let’s just do that one as an example, but I will mention at least this paper to start which is just a consideration of polyphenolic compounds in general, again, isothiocyanates are not polyphenolic, but is a chapter from a book about the inhibition of digestive enzymes by polyphenolic compounds.

Specifically, what they’re talking to here are tannins in plants. I don’t think we’ll debate the veracity of this finding that at least in vitro and likely in vivo consuming high tannin diets leads to lower amounts of protein absorption. They say the evidence for this is summarized and discussed in relation to the possible effect of enzyme inhibition, reduced nutritional value, and it’s concluded that observed reduction of protein availability found in vivo on consuming high tannin diets cannot simply be explained by the formation of dietary protein tannin complexes. That the ability of polyphenolic compounds to inhibit digestive enzymes may be of greater significance than realized previously.

This is just, again, it’s a chapter with a number of references, but there is evidence that polyphenolic compounds, specifically tannins, do inhibit protein digestion, proteinases throughout the body. Many animals that are primarily herbivorous like a moose, meeses, obviously is a joke, chew things, contain compounds in their saliva that inhibit these tannins. Rabbits are known to chew their food frequently and allow the tannins to aromatase or to become sort of–

Alex: They aerosolize.

Paul: They aerosolize, yes, thank you, from their mouth while they’re eating them. There are adaptations in herbivorous animals to these compounds and the assertion that I would make is that humans are probably not that adapted to consuming large amounts of these because of our history as primarily meat-eaters evolutionarily and that they can be harmful to humans. Now, there are also examples in the literature of agriculture of animals being encased in small grazing areas or overfeeding on certain plants and having very negative side effects or die-offs when their grazing lands are controlled.

I’ve heard the author of the paper Dealing with Phyton Chemicals in Beef, Provenza discussed this as well, that when you look at the way that animals behave and their consumption of plants, they’re eating a little bit of one, a little bit of another, and they seem to understand that if they over-consume these plants, they will have negative consequences. Similarly, if you administer antinausea agents to cows, they will over-consume these foods not having that sort of feedback from the negative compounds in plants.

Now, that specifically is probably an example of tannins or other polyphenols but it’s getting to the broader point that the plants do contain defense chemicals and that even animals that are primarily herbivorous need to take that into account when they are consuming them. If we specifically are thinking about isothiocyanates, this is a lightning rod conversation for sure. The most well-known isothiocyanate is sulforaphane and I’ve discussed frequently about this one but there are many isothiocyanates that may have the potential to be negative in humans at the level of ion absorption and the thyroid among other possible detrimental mechanisms.

This is an article looking at concentrations of different isothiocyanates, specifically thiocyanates and goitrin in human plasma. With an associated risk for hypothyroidism, again, we talked about the extreme example of this, the people with endemic goiter and huge necks in Africa. It’s not a question of whether this occurs it’s just a question of what is the severity of this and how effective are these compounds at blocking this.

Interestingly, sulforaphane wasn’t the worst at this but there were other isothiocyanates found in Brassica vegetables in this study at levels that would be commonly consumed that had the ability to considerably lessen radioiodine uptake at the level of the thyroid. As they say here, ‘In contrast, progoitrin, and indole glucosinolates degrade to goitrin and thiocyanate respectively and may decrease thyroid hormone production. Radioiodine uptake to the thyroid is inhibited by 194 micromole of goitrin, but not 77 micromole of goitrin.

Collards, brussels sprouts, and some Russian kale contain sufficient goitrin to potentially decrease iodine uptake to the thyroid. However, turnip tops, commercial broccoli, broccoli rabe, and kale belonging to Brassica Oleaceae contain less than 10 micromole of goitrin per 100-gram serving, can be considered a minimal risk.’

It’s just an illustration of the fact that these compounds do exist and are pretty clearly negative at the level of thyroid absorption of radioactive or at least iodine absorption for the thyroid. That’s just one example of isothiocyanates.

Now, people will argue on the other side that these compounds have benefits. I don’t know where we want to take this conversation because of their effect in the liver on the Nrf2 system. My response to that has always been that I think that there’s pretty good evidence or at least a compelling argument to be made that we don’t need compounds like isothiocyanates, be it goitrin or sulforaphane, to obtain optimal anoxic status when we have other things in our diet that may be activating Nrf2 system, that being exercise, fasting.

Even heterocyclic amines from the consumption of meat may do this. Many things in our diet and lifestyle may trigger the overall production of glutathione or manufacturing compounds, precursors, et cetera. That’s my overarching perspective on those and I’m happy to clarify, or I’ll just allow Alex to respond.

Ari: [crosstalk] [unintelligible] I think that was very thorough. Thanks, Paul. Alex, you want to go?

Does meat increase your risk of colon cancer?

Alex: Yes, I guess I have two questions. One of them is a slight tangent which is that, Paul, do you think that consuming meat causes colon cancer?

Paul: No.

Alex: Why? Briefly, if possible.

Paul: I think about that from a number of perspectives, both evolutionary, mechanistically, epidemiologically if you compare Asian studies. There’s a lot of evidence in that opinion that there is–

Alex: Let’s ignore observational evidence because you made that clear that that’s not reliable, let’s ignore evolution because that’s not dealing with long-term health, that’s dealing with survival and reproduction. Let’s focus on mechanisms. Red meat is classified as a probable carcinogen and processed meat is a carcinogen by the World Health Organization and the International Association for Research on Cancer, the IARC based primarily on established mechanisms that show how meat and the compounds it contains cause cancer in your colon cells. If that mechanistic evidence exists, why do you not believe that the inclusion of meat is problematic because there’s a mechanistic possibility or there’s a mechanistic route through which it causes colon cancer?

Paul: I’ll show this study which I think is probably the best summary of this that I’ve read. It’s a review paper. The title is Red Meat and Colon Cancer, a review of mechanistic evidence for heme in the context of risk assessment methodology. If you look at this paper, what they elaborate on is that the working group cited mechanistic evidence for multiple meat components, including

those forms for meat processing, such as N-nitroso compounds, abbreviated as NOC, heterocyclic aromatic amines, and endogenous heme iron. In this paper, they make a great case for the fact that many of these, though there are hypothetical mechanisms, again, have been studied very poorly.

Animal studies utilized models that tested promotion of preneoplastic conditions, utilizing diets low in calcium, high in fat, combined with exaggerations of haem exposure that in many instances represented intakes that were orders of magnitude 10 to 100X above normal dietary consumption of red meat. Finally, clinical evidence suggest that the type of N-nitroso compounds found after ingestion of red meat in humans consists mainly of nitrosyl iron and nitrosophyls, products that have profoundly different chemistries from certain N-nitroso species which have been shown to be tumorigenic through the formation of DNA adducts.

I think that in response to your question, I would say that many of the mechanisms proposed for any of the compounds in meat being tumorigenic carcinogenic are something that need to be considered more carefully because there’s certainly a large amount of evidence that it doesn’t hold up to intense scrutiny, which makes a lot of sense evolutionarily. Different types of N-nitrosophyl compounds, heme iron being studied in animal models, which are calcium deficient, orders of magnitude higher, et cetera.

Alex: The context around they had a really crappy diet, they were deficient in calcium, et cetera. How is this criticism of the red meat cancer any different from you saying that these goitrogens are problematic in societies that have inadequate iodine intake or under certain circumstances where they’re consuming incredibly excessive amounts of these goitrogens in their diet or in animal models that use isolated goitrogens to show that it has a negative effect on thyroid? To me, it seems like you’re applying a double standard to one set of evidence and you’re not applying that same standard to the other side of evidence because I don’t think that there is.

Correct me if I’m wrong here. For example, if you look at soy, soy has goitrogens in it. When you look at studies that assess actual thyroid function in people that consume large amounts of soy, you find that thyroid function remains unaffected. In fact, the longest randomized controlled trial that we had, which followed 403 menopausal women for two years, reported that consuming 120 milligrams of soy isoflavones daily over that two-year period had no significant effect on thyroid function other than a trend for reduction in T4. That reduction was from 1.2 to 1.1, which isn’t clinically significant by any extent.

Why are you focusing on these mechanisms that oftentimes happen under unrealistic as opposed to hard outcome data that looks at things like actual thyroid function when eating what would be considered the upper end of reasonable quantities of these foods?

Paul: I think that that study that I showed illustrated pretty clearly that within the realm of normal consumption of those species of brassicas, there were compounds, specifically goitrogen, that pretty clearly affected radioiodine uptake and could be [crosstalk]–

Alex: I agree, it did, it affected uptake, but it didn’t affect thyroid function, did it? Was that assessed? Because iodine uptake in actual thyroid function, like the secretion of T4 and transformation to T3 are two totally separate outcomes. Iodine uptake is also affected by how much iodine you have in your diet. It could inhibit uptake, but if you have enough iodine to compensate, that seems to be a non-issue.

Paul: My point is that there are many plants that contain chemicals that are clearly intended to have negative effects on animal-human physiology, whether it’s cassava, or goitrogenic compounds, and brassica vegetables. The question is, why would we eat those vegetables? Why would we even negatively affect thyroid function or any of the other potential issues with isothiocyanates when we could get all of the nutrients from those things from other foods like animal foods, animal meat, animal organs, et cetera? There’s a clear indication of the plant’s intention here and the intention is sinister.

There are plenty of good mechanistic studies as opposed to the poorly done mechanistic studies with red meat and cancer, or N-nitroso compounds, or heme iron that suggest that this is a mechanism that is damaging for humans so that we must ask the question, why would we include these things in our diet? To me, this is a really, really important conversation because there are literally hundreds of thousands, if not millions, hundreds of millions of people suffering with issues that are not resolved by Western medicine. We must ask these questions about whether all of these plants in their diets are completely benign.

Anecdotally, clinically, I see this over and over and over that people get better, whether it’s from a hypothyroid state, whether it’s from a GI issue state, inflammatory bowel disease, even irritable bowel syndrome when many of these brassica vegetables or other vegetables are removed from their diet. I think that it’s just beginning to ask the question about whether these plants are uniquely benign for humans because your position would be these plants are not harming you. I will tell you with complete certainty, Alex, that if you tell people that none of these plants are harming them, there are people who will not improve their quality of life because they will not consider this to be a possible negative influence on their health.

There are people that will continue to suffer. We must consider the fact that the intention of these plants is clear. These are negative compounds in our health. Are they going to affect everyone’s health negatively? No, certainly not. There are some people who may have enough iodine in their diet to be fine with it, but why would we eat plants, especially the most toxic defendant parts of plants that are not really improving our health as humans? This is the question I’m asking. I think that we have to be very careful to not forsake the people who are continuing to suffer.

We have to keep asking these questions. If someone is eating a diet containing kale or spinach, collard greens, and they’re thriving, who am I to tell them how to change their diet? I would never do that, but I think these discussions remain critically important for the people that are not well, that continue to suffer. I see it over and over and over that mechanistically, biochemically, there are so many of these defense chemicals, and that’s what I’m illustrating with that paper, that are not intended to be good for humans and that appear to have very negative effects for us.

Alex: Do you think instead of not being intended to be good for us, maybe that their effects are more accidental? The reason I say that is, again, if we go back to red and processed meats, there are compounds in there. Even though you say that that mechanistic data is of low quality, but other mechanistic data using similar conditions is not, which I don’t understand, but whatever. A lot of the stuff’s accidental, but why eat red meat? We can get all the nutrients we need in red meat from, for example, seafood and poultry. Why eat red meat and why risk consuming these nutrients that have a mechanistically plausible way of hurting us?

Paul: I got multiple questions there that I’ll answer in turn. I would disagree with you. There are many nutrients in red meat and organs that are not found in fish that are not found in chicken. Whether these be peptides that are unique to red meat, things like splenopentin or tuftsin or hepatic growth factor or BPC-157. It is simply an inaccurate statement to say that we can get everything that is found in red meat or ruminants in chicken or fish. I think it’s a splitting of hairs. I have no problem with people eating chicken and fish as long as the fish is not high in heavy metals, which usually is, not a huge fit for clear seafood consumption.

I think that if you look at the amounts of many nutrients, especially nutrients that we’re only now beginning to learn about, they’re not always evenly distributed and there are unique benefits to larger animals, specifically ruminants. That would be my answer to you. We can certainly discuss offline why the mechanistic studies with red meat are not accurate. I thought I discussed that clearly. I’m not sure what part of that you’re not understanding.

Ari: I think he’s more using it as a way of arguing rather than actually disagreeing, trying to argue that they’re harmful. He agrees with you.

Alex: I’m just using it to draw a parallel because a lot of the things you mentioned, low calcium intake, unrealistically high doses, those are the same conditions that are used with a lot of the mechanistic goitrogen studies.

Paul: Not the one that I showed.

Alex: No, but the one that you showed just looked at iodine uptake. It didn’t look at actual thyroid function.

Paul: It’s just the intention [crosstalk]–

Alex: I can pull it up if you want, but I have a meta-analysis and the longest RCT that’s been conducted showing thyroid function remains essentially unaffected. That’s a hard outcome that we care about. Iodine uptake isn’t.

Paul: Like I said, if someone is eating these foods and has normal thyroid function and feels great, eat them, I have no problem with that, but in people who are suffering, the intention of plants is very clear here. You used the word accidental and I want to really clarify that. There’s no accident here. In the case of sulforaphane, the precursor molecule is glucoraphanin. I often ask people and I’ll ask you guys this, do you know how much sulforaphane is in a broccoli seed?

Alex: A lot.

Paul: Do you have any idea?

Alex: I think broccoli sprouts are like 1,000 milligrams per gram or something like that.

Paul: The answer is zero until [crosstalk]–

Ari: [inaudible] in the seed rather than the sprout.

Paul: No, it’s zero until the sprouts are chewed. It’s zero until the seeds are chewed. The intention of plants is very clear here. There is no sulforaphane in a broccoli seed until you chew it. The reason it is made when you chew it is because myrosinase combines with glucoraphanin. Those are separated in terms of cellular compartments. It is the mastication, it’s the chewing of the broccoli sprout seed plant that makes sulforaphane and other isothiocyanates. It’s the same thing with cassava and allyl isothiocyanate and hydrocyanic acid. These are defense mechanisms.

These are booby traps that are sprung when different cellular compartments in the plant are combined via mastication. The intention of the plant is quite clear here. The plants are now– and I’ve often heard it said that sulforaphane, many of these isothiocyanates are so reactive from an oxidative perspective that they would create oxidative stress in a broccoli plant. They’re not used. It’s not a molecule that’s in a broccoli plant. We know this in humans. That’s the reason sulforaphane triggers the Nrf2 Keap1 system. It’s because it is reactive oxidative molecule. There’s no question about that.

A Broccoli plant doesn’t contain sulforaphane until it is consumed by an animal. It’s no accident. I hope I’m understanding your position properly here, but these compounds are not accidental. These are compounds that the plants are actively using as booby traps to prevent or dissuade consumption. There’s no question that plants contain anti-nutrients and defense chemicals. The only question is how well adapted any individual is to eating these compounds. Certainly, there are systems in our body to deal with them, phase I and phase II detoxification in the liver, but there’s inter-individual variation in terms of how we do this.

I think for some people, they are pretty problematic and the corollary assertion that I’ve made throughout this is that I don’t see a benefit to excluding them from the diet. It seems like a much safer proposition that is evolutionarily consistent to me. I just wanted to respond to those points. There’s no accident here.

Alex: Yes, that makes sense to me and I would agree. I would agree plant secondary metabolites are defense mechanisms. I guess when I said accidental, I was thinking specifically of human consumption, but in the grander scheme of things, I completely agree with you that most phytochemicals are produced as a means of either promoting consumption or trying to circumvent it depending on what part of the plant. I also agree with you that I think the individual does need to be respected and that some people might do better limiting certain foods depending on their individual physiology and biochemistry.

I don’t want to get caught in the weeds of that individuality because we both agree on it. We both agree there’s always going to be exceptions to the rule, but I want to focus on the rule because some people should minimize their intake of high goitrogen-containing foods, just like some people need to minimize their intake maybe of phytoestrogens if they have an estrogen-sensitive breast cancer. There’s a lot of examples of it, but you get my point. Certain individuals need different things. Some people might need to exclude all plants to really feel amazing if they have inflammatory bowel disease because the flares are just killing them.

As a general rule of thumb, if we were to give population-level guidelines for how the optimal diet should be built, that’s what I want to focus on. I would not say that the glucoraphanin or a glucosinolate in broccoli that acts as a goitrogen is problematic for people, especially because over half of it’s reduced by simply boiling the broccoli for five minutes. That’s the case with a lot antinutrients is that cooking, if we get into others, most of them like lectins, cooking destroys a lot of them, which reduces their activity. Now, a lot of people eat plants raw. That could be even more problematic than cooked plants and I agree. That gets back to the individuality thing.

From our conversation on goitrogens, yes, I agree that they are problematic in certain contexts. I disagree that the evidence supports a widespread problem of including more goitrogen-rich foods in the diet because I haven’t seen and you haven’t shared any data that shows that it actually has a negative effect on thyroid function outside of very specific circumstances such as insufficient iodine intake, consumption of maybe excessive amounts in that circumstance. It’s been a lot of mechanistic reasoning that is logical, it makes sense, but it doesn’t play out in the grand scheme of things because there’s a lot of other factors that come into play in our biology. Iodine intake’s one of those.

Ari: I have a devil’s advocate question for both of you. Paul, are you okay with me asking you a devil’s advocate question?

Paul: Can I just respond to that?

Ari: Sure.

Alex: Yes.

Ari: I’m just trying to ask a question here, but go ahead.

Paul: No, I think I agree with you, Alex. I think that it’s just important to consider that when we’re designing an optimal diet for humans, we need to have this consideration of plants as on a toxicity spectrum. For me, the question remains, why would we include these foods in our diet? Why would we include– Again, we’re getting to the point I think we may have to do a part two or something for this discussion because I think that nobody listens beyond this point. I wanted to keep it a little more succinct than this. I think that the question becomes, why would we include kale?

Why would we include brassica vegetables in the diet if they don’t have a unique benefit and there’s a potential mechanistically for harm? If we are going to design an optimal ideal diet for humans within those guidelines, we must have the caveat that, hey, many people feel better when they remove these foods from their diet. Many people feel better when they get these things out of their diet. There are plenty of instances of these things triggering people in very negative ways. There’s mechanistic science behind it, there’s interventional studies that are, again, with salmon, shrimp, and salmon eggs. on uptake rather than end thyroid outcomes suggesting the intention of plants as a defense chemical.

What I fear is that when we try and create a diet for everyone, we were making broad strokes that are often much too broad and that don’t serve individuals. How do we create then an idea of a framework of a diet for humans that also includes a very clear message that the exclusion of many of these foods, specifically what I might consider to be the most toxic plants, can be very helpful for people who are continuing to suffer? I think that’s what gets left out of these broad strokes conversations about human health.

I think that if the majority of people in the United States, in the world, ate a paleolithic type diet with organs and meat and animal fat and vegetables, human health would improve massively. It’s like you said in the beginning that if people ate an animal-based diet or a carnivore diet, I think the human health would improve massively as well. I think in either of those contexts, we have to have the discussion. This is what I believe has been left out and maybe the importance of this conversation. We must have the asterisk. We must have the consideration of the fact that these plants do not serve all humans very well.

That’s a statement that gets left out often because people will say, “Look at this data, look at this observational data. These are clearly beneficial for humans.” I feel like one of the unique aspects of the position that I’m taking here is to say, “Hey, this is not great for everyone.” Like I’ve said throughout this discussion, if somebody is thriving, doing well, don’t change your diet, but I want people to know when they are suffering, that these things are not uniquely beneficial for humans and this is why because this is where the plants are coming from and these compounds are clearly intended to be negative for us. I’ll let you respond to that if you want, or I’m happy to answer your question, Ari.

Alex: It would be your brief response Ari, 30 seconds.

Ari: Go for it.

Alex: I guess in my head though, when you mentioned that there are certain chemicals like bioactive peptides in animal foods that we can’t get in plants, I would make the analogist argument that a lot of the phytochemicals in plants we can’t get in animal foods. Even though we could get some, no doubt, we can’t get the majority and that even though the majority might have weak evidence behind them, I think you would also have to concede that a lot of these up-and-coming bioactive peptides would also have equivalently weak evidence, possibly even weaker.

It comes back to something you brought up earlier, which is that we need better data, and that’s something I wholeheartedly agree with. While I don’t think that this type of thing would be done ever, it would be cool to start seeing some studies that actually look at primarily carnivorous diets and compare them to equivalently quality diets that were richer in plant foods because that would answer a lot of questions. That would really help isolate all of these phytochemicals without the unrealistic scenario of looking at them in isolated high dose concentrations.

Paul: That actually makes me think of a question that I have for both of you. I don’t know if you were saying this, we didn’t really talk about this earlier in this detail. There are clearly compounds in animal foods that you cannot get in plant foods, B12, creatine, carnitine, choline, anserine, taurine, vitamin K2. There’s really not a lot of riboflavin in plant foods. This is really not even a topic for discussion to understand. There are many unique things that are necessary for optimal human health in animal foods.

Now, I think that it’s much more difficult to make the corresponding argument though your point is well taken that we would have to consider are these phytochemicals really valuable for humans, and do we really know which of them show up in animal foods and which of them don’t. The paper that I showed might suggest that maybe the ones that are beneficial for humans, a significant amount of them might actually show up in animal foods. I think that would be something that’s a topic for further discussion.

Ari: [inaudible] give example of that as well, showing up in salmon and shrimp and salmon eggs.

Alex: Yes.

Paul: Yes.

Ari: That is primarily [crosstalk] sources of that as well, unless you go seek out that algae, which I’m not aware of any human society that does that.

Alex: The closest I could think of would be spirulina, but that’s technically not an algae. It’s a cyanobacteria. The natives off of Lake Chad in Africa and Tanzania and Central America have that as a staple of their diet. Interestingly enough, it’s also a bioavailable source of vitamin B12 that is usable by humans in quantities that could satisfy B12 requirements. Although no study I’m aware of has actually looked at if it could prevent a deficiency because that would take a really long time. It contains the cobalamin molecule.

Paul: Interesting. It seems like it’d be much easier to just eat animal foods.

Alex: I agree.

Ari: Do you guys want to do fiber or are we going to end?

Paul: I think we should wrap it up. We can’t do fiber, it just gets to be [crosstalk]–

Alex: I think fiber would be a cool one to do within a follow-up.

Paul: Can I ask you guys a question?

Ari: Go for it.

Paul: Have either of you ever done a carnivore diet or an animal-based type diet?

Ari: Animal-based? Yes, certainly, not to the exclusion of plants.

Paul: By animal-based, I mean the way that I’ve talked about it with the exclusion of nut seeds, grains, legumes, leafy greens, stems, and roots. Have you done that, Ari, just meat and fruit and organs?

Ari: When I was doing heavy meat, it was more of an extreme low-carb keto approach, so no fruit and honey.

Paul: Were you including any organs in your diet?

Ari: Yes.

Paul: You were?

Ari: Yes. Liver and heart.

Paul: Cool. What about you, Alex?

Alex: Yes. I don’t know. This might have been back in 2014, I think. My diet was based around meat, like chicken, bison, chicken hearts, beef liver, eggs, and cheese. Then the primary plants in my diet were potatoes for starch, a big salad at lunch, and coconut.

Ari: Why do you ask?

Paul: I’m just curious because I think that personal experience is valuable. I have my own story of basically eating a paleolithic diet and having pretty bad eczema and then excluding the majority of plant foods and having that improve. I wasn’t sure if either of you had experimented with something like that to see how your body reacted.

Ari: I’ve done probably every extreme diet than you can imagine in my teens and 20s. I agree completely with what you said. I’ve done vegan, I’ve even done raw vegan for a [unintelligible]. I can’t say those experiments ended well at all, but my low-carb keto, heavy animal food diets also didn’t end great, especially just as an athlete. Notable decrements in performance for sure. Other than that, I can’t say I noticed much of an effect. Alex, do you want to jump in with your experiences?

Alex: The whole reason I got into nutrition was because I did a decade of competitive wrestling that gave me an eating disorder. I’ve always just been able to push my way through any diet I’ve been on with willpower. I probably feel best where I’m at now, which is just a mix of plants for starches, probably less fibrous vegetables than I’ve eaten historically. Then continue to eat high-quality lean meats. Most of my fat comes from plant sources, all of my fiber from plants, then resistant starches from cooked and cold starches, but meat provides half my nutrients and all of my protein.

Paul: I will say, Ari, that a lot of people experience that on ketogenic or low-carb diets and that’s one of the reasons that I re-incorporated carbohydrates in my diet from sources that seem to work both for me. That’s why I think that there should be a consideration of those macronutrients a little bit.

Ari: I applaud you for not being so dogmatic in that belief system, especially being an author of a book on that subject. It’s, I think, easy to lock ourselves into our belief system where we become inflexible and unable to adapt. I know I’ve been there many times with different extreme diets where I’ve been so convinced of that diet being the ultimate truth that– It basically created an eating disorder as far as inflexibility of being willing to deviate from that. If you guys are cool with it, I’d like to ask one devil’s advocate question to wrap up.

Paul: I’ll just mention in response to your statement, Ari, that as I said in the beginning, even when I wrote the book, I don’t think it was dogmatic or extreme, there were considerations that allowed for some flexibility. I just want to make that very clear because you seem to continually try and paint me differently.

Ari: I’m always happy to give you the opportunity to clarify. Apologies if you feel I’m misrepresenting. Alex, I would like to ask you if, and to this point, Paul, if you feel I’m misrepresenting things please correct. I would like to ask you, Alex, if you think it’s possible that this whole body of nutritional epidemiology for the last 70 years and the thousands of studies on that that have pointed towards plant-based diets being the key to health. I would say if there’s one point of agreement that historically everybody on the different dietary spectrum has agreed upon it’s that the vegetables are healthy.

In this podcast that’s been debated. Do you think it’s possible that mainstream thinking around nutrition for many, many decades just we could have gotten that badly wrong and all of the studies that have pointed in that direction could be flawed?

Alex: I think it’s possible that eating a diet with little to no plant food could be healthy. I don’t think we have data to support that and I think what data we do have looking at meat-heavy diets is heavily confounded by unhealthy user bias and also by the types of meats being consumed. However, I would hypothesize based on what evidence we do have available that a meat-heavy diet that perhaps reduced its meat and replaced much of it with plant foods, not just any plant foods, but specifically replaced it with fruits, fibers, vegetables, and legumes, would be probably much healthier.

That will get into hopefully a follow-up discussion we had about fiber. I also do think that there isn’t sufficient data to support a detriment of anti-nutrients such lectins, phytates, goitrogens, phytoestrogens, or phytoestrogens in certain plant foods when it comes to actual hard outcomes in humans, even if there is mechanistic plausibility, especially under the context of a nutrient-sufficient diet. I think there’s more possibility that a plant-heavy diet is detrimental under conditions of, for example, poor socio-economic status or developing countries where they’re not getting a lot of these bioavailable nutrients that are supplied by animal foods.

Therefore, these anti-nutrients wreak even greater havoc. We go back to that goitrogenic example, low iodine intake with high intake of goitrogenic foods, bad case of goiter. I think under nutrient adequacy supplied by a combination of plant and animal foods, I don’t think that these anti-nutrients I don’t think they are detrimental to our health and I think that there is a good body of evidence supporting the beneficial effects, even if we haven’t figured out every single mechanistic reason why of a lot of these secondary plant metabolites that go outside of just the vitamins and minerals that they provide.

Just like, I think, that there’s a lot of benefits from certain zoonutrients that are present in animal products, things you can’t get in plants, like carnitine, creatine, taurine. I think a lot of these bioactive peptides, bioactive amines, that type of thing, also have benefits and we can’t get those from plants.

Ari: Excellent. Paul, my question to you is, correct me if I’m misrepresenting, if plants are, let’s say, a net negative, is that agreeable, or in the majority of people that high plant food consumption is net harmful rather than net positive?

Paul: What’s your question, Ari? I’m not understanding why you’re [crosstalk]–

Ari: That’s okay.

Paul: No, we’ll see.

Ari: If that is the case, how could so many studies, epidemiological, flawed as they may be, healthy user bias incorporated, but given that many of these studies try to control as much as possible for a lot of those confounding variables like smoking and exercise habits, how could so many point in that direction and how could there be so many anecdotes of, let’s say vegan. Remember, I’m not a vegan or an advocate of veganism, but how could there be so many vegans who go entirely plant-based where their whole diet is composed of things that you’re saying have sinister intentions and yet report such positive health effects and reversal of diseases and so on?

Paul: I believe you’re asking me multiple questions. I will answer the vegan one first. I think that, again, the devil’s in the details. This is the problem with considering the weight of the evidence, but if you look at these instances, again, we don’t have specific vegans here to ask about the improvements in their health, but I think it’s pretty clear that the main offender, as we said from the beginning, is processed sugar and seed oils and the processing of food. Despite the inclusion of anti-nutrients in their diet, moving from a diet containing more toxic things to a diet containing relatively less toxic things could lead to health improvements.

Now, interestingly, as I touched on earlier, if you look at long-term vegan nutrient adequacy, it’s abysmal. I think that that is an indication of lower bioavailability and overall content or overall presence of antinutrients, or at least digestive enzyme inhibitors, things that block absorption of nutrients on an entirely plant-based diet. To bring good old Joel back into this conversation, long-term vegan diets are a nutritional nightmare for humans without massive amounts of supplementation because plant foods simply do not contain adequate nutrition for human beings. That is very difficult to argue. I feel very strongly about that.

Though people may improve in the short term, they ultimately have just a flaming crash of the airplane later on when they run into all sorts of health problems with these diets. You could improve a fast, you could eat no food and see an improvement. You mentioned this earlier with regard to the potato diet and other diets. It’s really important to consider that many of the studies with vegan vegetarian diets are calorie-restricted as was the Twinkie diet, as are these potato diets because you simply cannot eat enough calories from potatoes.

Anyone with metabolic dysfunction is going to see an improvement in their overall health in insulin sensitivity when they have calorie-restricted diets. Even if those calorie-restricted diets are composed of some of the least bio-available nutrients or foods that are what I would consider to be less optimal for humans, they’re going to see an improvement at least in the short term, but I think long-term studies bear out the fact that there are problems with these foods both in the absolute amounts and bioavailability of nutrients.

I would suggest from the perspective of the fact that many of these nutrients are much harder to absorb, or these antinutrients like phytic acids or oxalates, like we discussed with the zinc study, can impair the absorption of minerals from other foods that might even be animal containing. That’s the answer to your first question. Well, that was the second question you asked. The first question you asked which was, why do so many observational studies point to a benefit with these plants? I think we discussed that earlier pretty in-depth, having to do with healthy user bias with unhealthy user bias. I’m not sure we really need to go into that in detail.

Ari: [crosstalk] the second part.

Paul: You and I discussed this a little bit in our previous meeting. I think that there are no good studies that have been done looking at high vegetable and low vegetable populations from an observational perspective and it just doesn’t exist. When we look at these studies, they’re generally all of the people in them are eating vegetables at moderate amounts. It’s hard to see a signal of epidemiology and as we talked about in this podcast, I think that this may be one of the cases where we have to think about whether we lose the individual, and individuals continue to suffer when we consider that other research as a primary means of making the decision.

Ari: Guys, thank you so much for all of the time. This has been a lot of fun. Thank you for also being so polite and respectful and being willing to agree when you actually agree on certain things. This was awesome. Paul, thank you for being brave enough to come on after we met in-person and had a brief scuffle, so you knew we had some disagreements going into this. I know you’re a bit wary of a two-on-one dynamic. I did my best to leave out most of my commentary of this. I know you got mad at me a couple times there, but hopefully, I was good enough to be relatively unbiased in moderating this discussion. Guys, thank you so much. This was awesome and, hopefully, we can do it again.

Alex: I would like a follow-up on fiber because I think that’s just a fun topic to talk about and I really like fiber. As a discussion topic, I think it’s interesting because there is a lot we actually don’t know. I think that it would be interesting to see what agreements me and Paul could come to on that, just like we did here.

Ari: Paul.

Paul: I appreciate you guys. Thanks for coming on, Alex. I enjoyed it. I think it’s fun, and we should keep sharing ideas. I think this is what moves things forward and it’s what we need to do more of. I appreciate you hosting, Ari. It’s good to have a moderator, though as I said, I think it’s important the moderator remains– [chuckles]

Ari: Trust me when I tell you there was about 500 times I wanted to interrupt you and say certain things and I restrained myself.

Paul: Appreciated that.

Ari: I did the best I could on that front given that we are humans; we all have our own biases. Thank you, guys, again. To all the listeners, I guess the debate lives on. You have to decide which arguments you felt were more compelling around plant foods being helpful, or harmful, or benign, and where you fall on that. Thank you, guys, again. This was a pleasure. I hope to talk to you both again in near future.

Alex: Yes.

Paul: Thanks, man.

Alex: Later.

Ari: See you guys.

Show Notes

The main contributors to disease (03:22)
What is the most healthful diet? (06:11)
How healthy user bias influence science (29:29)
Are plant foods healthful or harmful? The problem with many interventional studies (42:54)
Do plants cause goiters? (56:56)
Are fruits healthful or harmful? (1:07:27)
How plant compounds end up in meat (1:10:27)
How certain foods when eaten in excess may cause harm (1:17:00)
Does meat increase your risk of colon cancer? (1:28:00)

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