In this episode we discuss:
- All organisms are shaped by their environment
- Vegan diets are lacking in key nutrients
- The trouble with epidemiological studies
- Clinical research quality varies widely
- News articles should not be used as evidence
- The source of the message matters
Chris Kresser: Hey, everybody. It’s Chris Kresser. Welcome to another episode of Revolution Health Radio. This week we have a question from Beth. Let’s give it a listen.
Beth: Hi, Chris. My name’s Beth. I’m wondering if you can comment about your reaction to the What the Health documentary that’s on Netflix and quite popular right now. I have the BRCA 2 mutation and have known for about three years, and I’m feeling pretty defeated when looking towards the way to eat to prevent breast cancer. I feel like when this journey started out I was vegan, did a bunch of research, and experts pointed me towards Paleo. What the Health documentary, every time you get new information, you feel pulled in that direction. So would love your thoughts. Thank you.
Chris: Well, we received several questions about the What the Health documentary, not just from Beth, and thank you all for sending those in. They were all quite similar, so I’m just going to consolidate the answer here to Beth’s question because I think it will cover everybody’s question.
At least once or twice a year over the past several years there’s been some big media story suggesting that red meat or eggs will kill you or a plant-based diet is the best choice or that vegetarians live longer than omnivores or other such unfounded claims. Every year a slew of researchers, scientists, and other critics, including me, debunk these stories. I will admit that it gets a little bit tiresome saying the same thing over and over again, but I’ve come to accept that this is just part of my job. It’s part of my role. Fortunately, in the case of What the Health, it’s such a shockingly inaccurate and biased documentary that by the time I got around to writing about it or addressing it, it had been widely criticized by experts across the entire spectrum. Because of that, I didn’t write a critique as I typically would. There’s even an article by a vegan dietician, believe it or not, that slams the claims made by What the Health. That alone should tell you something, but clearly there is a need for more attention here because I still get questions. In fact, I had a few family members over the past few weeks send me an email and say that they have watched this documentary and they were concerned about their current diet and wondering if I had seen it and if I thought that they should consider a vegan diet.
What the $#@! Is Wrong with What the Health?
Now a podcast isn’t the best venue for a point-by-point rebuttal of the ridiculous claims made in What the Health, so I’m going to link to all of the best-written pieces in the show notes on my website, and at the end of the episode I’ll give you the link for that so that you can click those links, read the articles, and follow those arguments in a more explicit way if you want to do that. I’m also going to link to all of my previous articles, or at least the most salient ones, debunking claims that red meat and eggs cause heart disease and cancer and reviewing research showing that vegans and vegetarians are typically at much higher risk of nutrient deficiency. In this podcast I’m going to give you a broader overview of what’s wrong with this movie and why it shouldn’t have any impact on your diet choices.
All Organisms Are Shaped by Their Environment
When we’re evaluating claims about the best human diet, we have to look at it from two angles. One is an evolutionary perspective, and the second is modern epidemiological and clinical evidence. As we’ll see, What the Health fails miserably on both counts. The evolutionary perspective is important because it informs us about what a natural human diet really is. The evolutionary biologist Theodosius Dobzhansky once said, “Nothing in biology makes sense except in the light of evolution.” What he meant was that all organisms are adapted to survive and thrive in a particular environment, and when that environment changes faster than the organism can adapt, a mismatch occurs. For 66,000 generations, humans ate primarily meat and fish, wild fruits and vegetables, nuts and seeds, and some starchy tubers and plants.
There were some differences, of course, in the ancestral diets geographically. The Inuit typically have a very high-fat diet and low carbohydrate intake because of the limited availability of plant foods in that part of the world, whereas people like the Qatabans and Tukisenta in the South Pacific, where fruit and starchy tubers like sweet potatoes are readily available, tended to eat a high percentage of calories as carbohydrate. But despite those differences, the ancestral human diet shared a lot in common. They weren’t eating cheese doodles, processed and refined foods, but they also weren’t vegetarians or vegans. In fact, no human population in the history of civilization has ever been recorded surviving on a vegan diet, and again, that alone should tell you something. There are few, if any, known human populations that even followed a vegetarian diet exclusively, and if they did it was usually not by choice. They would often go to great lengths to trade with other local peoples for prized animal foods, for example.
So why does this matter? Well, as I just said, all organisms are shaped by their environment, and that’s true from the bottom to the top of the food chain. We consider bacteria that live very deep in the ocean near hydrothermal vents where there’s no light at all, they’re able to survive remarkably and most other organisms on this planet require light or photosynthesis, whether they require it directly or whether they consume foods that require it. But these bacteria that live near hydrothermal vents use sulfur compounds, particularly hydrogen sulfide, a chemical which is highly toxic to most known organisms, to produce organic material through the process of chemosynthesis. This is a great example of an organism that has been highly shaped by its environment. If you take those hydrothermal bacteria and you drop them into a shallow ocean that’s exposed to light, they’ll die.
Cats are another example. Cats we’ve known for some time, but it’s now more recognized by veterinarians that cats are true carnivores. They don’t eat anything other than meat in their natural environment, and that’s why you see now if you go into a pet food store, you’ll see that all of the premium cat foods say “meat only,” and often raw meat, because that is the way that cats would eat in their normal natural environment. I even remember a story a while back about a vegan couple in France, I think, who had almost killed their cats, essentially, by feeding them a vegan diet. So this is just one small example of where ideology can go wrong when it doesn’t match with the evolutionary perspective.
Zookeepers are aware of this as well. There has been a growing movement in zoos to feed animals the diet that they would typically eat in their natural environment and this came out of the recognition that animals were getting sick in zoos. At first they weren’t sure why. But then somebody actually brought this to light and suggested that, “Hey, maybe these animals are getting sick because we’re feeding them things that they’re not adapted to eat and that they wouldn’t be typically eating in the wild.” And now there’s been a much bigger movement to address that to the great benefit of the animals that are living in these zoos.
Vegan Diets Are Lacking in Key Nutrients
Humans are omnivores. We’re not true carnivores like cats, and this means we can eat both plant and animal foods. Our diet is not as limited as the diet of a hydrothermal bacterium or a cat, but like all other organisms and animals, we require a certain mix of things to survive. In our case, a certain mix of macronutrients—protein, fat, and carbohydrates—and micronutrients to thrive. It does not make sense from an evolutionary perspective that the best human diet is one that is lacking in nutrients that are essential to our health, yet that’s exactly the case with the vegan diet. The biggest issue is that it’s lacking in B12 and vitamin D. A common myth amongst vegetarians and vegans is that it’s possible to get B12 from plant sources like seaweed, fermented soy, Spirulina, and brewer’s yeast. But plant foods that are said to contain B12 actually contain B12 analogues that are called cobamides that block the intake and utilization of B12 and can actually increase the need for true B12. This explains why recent studies that use much more sensitive methods of detecting deficiency have shown that 83 percent of vegans are B12 deficient compared to just 5 percent of omnivores.
There’s also no vitamin D in a typical vegan diet. There are some obscure species of mushrooms that can provide large amounts of vitamin D, but these mushrooms are rarely consumed and they’re pretty difficult to obtain. This explains why vitamin D levels are 58 percent lower in vegetarians and 74 percent lower in vegans than in omnivores.
But a vegan diet is low in other key nutrients as well, including calcium, iron, zinc, EPA, DHA, and vitamin A. There are some crucial concepts that you need to understand when evaluating diet claims, and one is bioavailability. For example, although vegetarians often have similar iron intakes to omnivores on paper, it is more common for them and especially vegans to be iron deficient. Why? Because iron and animal products, which is called heme iron, is far better absorbed and assimilated, aka “bioavailable,” than ferrous, or non-heme, iron found in plant foods. The same is true with calcium. On paper, calcium intake is similar in vegetarians and omnivores, probably because both eat dairy products, but it’s much lower in vegans who are often deficient. But calcium bioavailability from plant foods is affected by their levels of oxalate and phytate, which are inhibitors of calcium absorption and thus decrease the amount of calcium the body can extract from plant foods. While leafy greens like spinach and kale have relatively high calcium content, the calcium is not efficiently absorbed during digestion. One study suggests that it would take 16 servings of spinach to get the same amount of absorbable calcium from an eight-ounce glass of milk. That would be 33 cups of [raw] baby spinach, or around five to six cups of cooked spinach.
Another important concept to understand is the difference between precursor and active forms of nutrients. EPA and DHA are the long-chain omega-3 fats. They’ve been universally recognized as crucial to health, and they’re a really good example of the important difference between precursor and active forms. Plant foods do contain linoleic acid and alpha-linolenic acid. Those are the precursor fats, which can be converted in the body into EPA and DHA, which are the ones we really need. While it’s possible for some alpha-linolenic acid from plant foods to be converted into EPA and DHA, that conversion is poor in humans. It’s about 5 to 10 percent of ALA going into EPA and about 2 to 5 percent of ALA getting converted to DHA. This probably explains why vegetarians have 30 percent lower levels of EPA and DHA than omnivores, while vegans have 50 percent lower EPA levels and nearly 60 percent lower DHA levels.
Another example is vitamin A. Retinol is the active form of vitamin A, and beta carotene is the precursor. The idea that plant foods contain vitamin A is a common misconception. Plants actually contain beta carotene, the precursor form. While beta carotene is converted into vitamin A in humans, that conversion is very inefficient. For example, a single serving of liver per week would meet the RDA of 3000 IU of retinol. To get the same amount from plant foods, you’d have to eat two cups of carrots, one cup of sweet potatoes, or two cups of kale every day. Moreover, traditional cultures consume up to 10 times the RDA for vitamin A. It would be nearly impossible to get this amount of vitamin A from plant foods without juicing or taking supplements.
The third concept you need to understand to evaluate diet claims is nutrient synergy. Most nutrients require the presence of other nutrients called cofactors to be absorbed and utilized. Now, we just talked about how very little of the plant-based ALA gets converted into DHA. Well, that conversion depends on zinc, iron, and B6, which vegetarians and vegans are less likely than omnivores to get enough of. This can lead to a double whammy effect where vegans are not eating preformed DHA, but they’re also eating less of the nutrients required to convert the precursor plant fat ALA into the active EPA and DHA.
Now, finally, the fourth concept to understand is anti-nutrients, or nutrient inhibitors. There are many substances that impair the absorption of nutrients. We talked about oxalate and phytate impairing the absorption of calcium, but that’s not the only nutrient that they impair the absorption of. The absorption of non-heme, or plant-based, iron is inhibited by several commonly consumed substances such as coffee, tea, and dairy products because of their calcium, supplemental fiber, oxalate, and phytate. But none of these substances with the exception of calcium has a significant effect on the absorption of heme iron from animal products. Again, this explains why vegetarian diets have been shown to reduce plant-based iron absorption by 70 percent, but total iron absorption by 85 percent.
Zinc is another example. Many plant foods that contain zinc also contain phytic acid, which inhibits zinc absorption, and vegetarian diets tend to reduce zinc absorption by about 35 percent compared with omnivorous diets. This explains why even when the diet on paper meets or exceeds the RDA for zinc, deficiency may still occur. In fact, one study suggested that vegetarians may require up to 50 percent more zinc than omnivores for exactly this reason. At an absolute minimum, if you’re following a vegan diet, you’d have to supplement with B12 and vitamin D to maintain health. But more likely, given the statistics that we just discussed, you’d also need to supplement with retinol, or the active form of vitamin A, EPA and DHA, zinc, iron, and calcium.
I hope it’s clear that it makes no sense to claim that a vegan diet is optimal for humans if you have to supplement it with several nutrients to make it work. This is ridiculous, I think, from an evolutionary perspective. We wouldn’t even be here to have this conversation and human evolution would never have occurred as it did on a vegan diet.
Let’s move on to the epidemiological and clinical evidence that was used in What the Health. The journalist Nina Teicholz did a point-by-point analysis of the so-called “science” in What the Health. I’m not going to go into that level of detail here, but we will link to her article in the show notes so that you can go check it out, but here are some key points that I want to highlight.
The Trouble with Epidemiological Studies
Number one is that most of the claims made in the film are based on epidemiological studies. These are limited in that they can only show a correlation, not causation. If you’ve been following my work for any length of time, you’ve heard me say this over and over again. One of the first things you learn in research methodology, which clearly the creators of the film have not studied, is that correlation is not causation, and there are a lot of fun examples of this you can find online, such as the number of people who drowned by falling into a swimming pool correlates with the number of films that Nicolas Cage appeared in, or the per capita consumption of cheese correlates with the number of people who died by becoming tangled in their bed sheets. I think it’s probably pretty clear that this doesn’t mean that people drowning in pools causes Nicolas Cage to appear in more films or that eating more cheese causes someone to die by becoming tangled in their bedsheets. That’s absurd. Yet this is often the kind of leap that is made in popular media articles or, in this case, What the Health that is trying to extract causation from studies that were never designed to prove a causal relationship.
Epidemiological studies are designed to generate hypotheses which then need to be verified with clinical trials or other experiments. Epidemiological studies also have other limitations, for example, the extreme unreliability of food frequency questionnaires, which depend upon people accurately remembering what they ate over the last six to 12 months. I can’t even remember what I ate six days ago, and I pay more attention to my food than most people I know. Another issue with epidemiological studies is that they can’t fully adjust for confounding variables. For example, let’s say they’re looking at people who eat more red meat, they will usually try to control for the most obvious variables like smoking and physical activity, but they’re not looking at things like the status of their microbiome, how much they’re sleeping, or other healthy or unhealthy behaviors that they might be engaging in. It’s virtually impossible to design a study that will be able to control for all of the confounding variables that we know about, much less the ones that we don’t know about. We now know, for example, how important the microbiome is to health, but I’m not aware of any studies that are controlling for differences in the gut microbiome as in the research design. That’s a huge problem. For all these reasons, scientists in most fields with the exception of nutrition, which tends to be out in its own world when it comes to this stuff, I agree that small associations with risk ratios of less than two are not really reliable in epidemiological research.
Clinical Research Quality Varies Widely
Number two, clinical trials are generally more reliable than epidemiology, but the quality of them still varies considerably depending on several factors: Was the trial randomized? Did it have a control group? Was it sizable? Was it on a relevant population? Did enough people finish the trial to make it meaningful, and do its results and do the data actually support the claim made in the conclusion? You might be surprised how often the researchers’ own data don’t match their conclusion.
News Articles Should Not Be Used as Evidence
Number three, newspapers, magazine articles, and blog posts are not rigorous sources of evidence. They can be informative and they can be helpful in summarizing the existing evidence, especially when they link to it, but they aren’t considered valid ways of scientifically backing an argument. With all of this in mind, Teicholz ranks the evidence presented in What the Health and, as she says in her conclusion,
In sum, 96 percent of the data do not support the claims made in this film. The film does not cite a single rigorous randomized controlled trial on humans supporting its arguments. Instead, What the Health presents a great deal of weak epidemiological data, case studies on one or two people, or other inconclusive evidence. Some of the studies cited actually conclude the opposite of what is claimed.
There are many other critiques of the science in What the Health out there on the web right now, including one from science-based medicine, a critical review by a vegan dietician, which I mentioned earlier, and a point-by-point takedown on Vox. We’ll link to all of these in the show notes.
The Source of the Message Matters
But one last thing that we need to talk about before we finish up, and that is agenda. The two producers behind the film are Kip Anderson and Keegan Kuhn, who are vegans and animal rights activists. As Nina Teicholz writes in her conclusion,
The majority of papers turn out to be posts by vegan diet doctors, namely Michael Greger and Neal Barnard. Both of these men are passionate animal welfare activists, so one can never know if they’re seeking truth about a healthy diet or if stated from the premise that they’d like to end all domestication of animals and proceed to cherry pick the science back from there. Given the weak to nonexistent data presented in the film, the latter seems to be a pretty good possibility. In fact, What the Health on zero sound science is quite likely a piece of animal welfare advocacy masquerading as a public health film.
That’s exactly the problem. We know from drug research that industry-sponsored trials, or studies paid for by pharmaceutical companies, are much more likely to report favorable results than independent trials because of biased reporting, biased interpretation, or both. This is a well-established phenomenon, and it’s been explored in both the media and the scientific literature. It really shouldn’t be surprising. The fact that this film is made by two vegan animal rights activists doesn’t necessarily invalidate its conclusions, but the fact that they only included experts and doctors that share their views, cherry-picked weak studies and unreliable sources like blog posts to support their argument, and ignore the huge body of credible scientific evidence that contradicts their claims makes this film a dangerous piece of propaganda rather than a factual report on human health and diet.
Okay. That’s it for today. I hope you found this to be helpful and informative. Head over to chriskresser.com/what-the-health to find a comprehensive list of critiques of this documentary and articles with real science and research that debunk its fundamental claims.
Okay. Keep sending me your questions at chriskresser.com/podcastquestion. I hope you’re enjoying the show, and I’ll talk to you next time.