November 3, 2019

Understanding science

Is ditching meat a “game-changer” for your health?

A new documentary makes the case it is.

Read Time 9 minutes

There’s a new documentary making the rounds, “The Game Changers,” which makes the case that going vegan can improve athletic performance and is the superior diet for human health. On the other side of the coin is meat, fish, fowl, eggs, and dairy—foods that not only can hamper physical fitness—they can promote erectile dysfunction, endothelial dysfunction, and lead to heart disease, cancer, and type 2 diabetes. Also, meat is destroying the environment.

I guess I’m starting to accept that such debates are never going away. Ever. Unlike science, which generally converges to truth, I don’t think nutrition (like religion or politics) is really capable of such convergence, especially when it comes to the most hotly contested vector of nutrition—dietary restriction. [If you need a primer on nutrition and its three vectors—dietary restriction, time-restriction, and caloric restriction—PLEASE pause for a moment to watch this short video explanation.] 

There are many things wrong with this film. And there will be no shortage of people—some credible and thoughtful, many deceptive and thoughtless—who will attack this film. I find that this particular topic to be more about ideology than fact and science; in fact it’s the worst kind of ideology because it cloaks itself in what looks like science. At least we recognize religion and politics for what they are, I suppose. 

If I’m going to contribute anything to this discussion, let me do so on two points related to this film that are not likely going to get a lot of attention. 

1) Switching from the Standard American Diet (SAD)—a diet of zero DR/CR/TR (see above video to understand what this means)—to a fill-in-the-blank diet is going to improve people’s health. Full stop. That includes vegan and vegetarian diets. That includes keto diets. That includes Mediterranean diets. That includes an all potato diet. But this observation tells you nothing about how healthy a “plant-based” diet is compared to one that is “meat-based.” 

2) Vegans and vegetarians are probably some of the most health-conscious people on the planet. This also means that when you compare these people to the general U.S. population, avoiding meat is but one of a myriad of differences between them. Observing differences in health outcomes is relatively easy. Determining the cause of those differences is virtually impossible. 

Let’s address these in order.

1 | The problem with using the Standard American Diet (SAD) as a control group.

What often happens, either in the volumes of observational epidemiologic studies that get cranked out every day or, less commonly, in films like this, is that a vegan or vegetarian diet is compared to the SAD, with the SAD as stand-in for a “meat-based” diet, as if the only difference between the two diets is one eschews animal foods. Take a look below at the top 10 sources of Calories in the U.S. diet circa 2010. You tell me, that even if you think meat is a problem, tell me that meat is the only problem with this list. 

  1. Grain-based desserts (cakes, cookies, donuts, pies, crisps, cobblers, and granola bars)
  2. Yeast breads
  3. Chicken and chicken-mixed dishes
  4. Soda, energy drinks, and sports drinks
  5. Pizza
  6. Alcoholic beverages
  7. Pasta and pasta dishes
  8. Mexican mixed dishes
  9. Beef and beef-mixed dishes
  10. Dairy desserts

I don’t think anyone would look at this list and question why Americans are so overweight and so sick. (By the way, there is not one item on this list that I do not absolutely love, except for #4. So I’m completely empathetic to the plight of anyone reading this who also craves these foods. They make up our default food environment and until that changes, we’re in for a rough ride, as a society.)

In the film, Bryant Jennings, an American heavyweight boxer, who stopped eating meat in 2013, and went vegan in 2015, talks about his conversion. “I grew up not even knowing about half of these other vegetables. Asparagus to me just came out like five years ago . . . My early years growing up in Philly, the only thing we knew was spinach in a can, collard greens and Popeye’s, KFC, everybody frying chicken,” says Jennings. “Most people say, ‘Oh, where do you get your protein?’ As if everybody that’s in KFC is looking at the back of a bucket, like, ‘Yeah, how much protein is [in here]?’ You all don’t know . . . You all don’t know what [you’re] eating. I’d never really thought about it like that before. What else was in the food I was eating?”

Jennings made the dietary switch for health reasons. “I just thought healthy eating, clean eating was much better. And it really has been great for me. . . Lots of peanut butter and jelly, oatmeal, quinoa, avocado, a lot of fruit and vegetables. I make my own burgers from scratch with chickpeas, black beans, lentils, quinoa, flax seeds, chia seeds. It’s all wholefoods,” he told The Guardian. In other words, Jennings went from fast foods to whole foods.

Typically, when people make the switch from the SAD to a vegetarian or vegan diet, it doesn’t just mean they’re striking a few numbers (3 and 9 in the case of vegetarians, and in the case of vegans, 5 and 10, too) from the top 10 list and adding in more sugar-sweetened beverages, grain-based desserts, and bread. They didn’t have a list to begin with. They weren’t paying attention to what they were doing, as Jennings points out. When people make a conscious decision to go from SAD to a vegan or vegetarian diet, they’re not going from a SAD to a “plant-based SAD.” Their diet, and often other aspects of their lifestyle that may impact their health, changes in myriad ways.

They eat more vegetables, fruits, legumes, whole grains, and nuts and seeds. They eat less refined carbohydrates, sugar, and saturated fat. They exercise more and may put more of an emphasis on stress management as well as social support (as Dean Ornish’s program includes, for example). During the transition, they may quit smoking, quit or reduce the consumption of alcohol, and focus more on getting adequate sleep. While we could debate the evidence for and against each one of these interventions, the point is that there are many changes taking place, in addition to cutting out animal products, that are consistent with what many people believe to be healthy living.

At the other end of the spectrum, we have the SAD. Not only does it represent the foods in the top 10 list above, but it also tracks more closely with many behaviors that are not consistent with healthy living. Less likely to exercise, more likely to smoke, etc. What was the change, or what were the changes, that improved the health of people transitioning away from the SAD? The problem is that when you have so many variables that can and do change—often simultaneously—when leaving the SAD, it is an experimentalist’s and an epidemiologist’s nightmare.

2 | The healthy user effect.

In “The Game Changers,” there are several studies and articles [see a complete “List of studies” at the bottom of this post] that flash on the screen comprising “overwhelming scientific evidence connecting animal foods to many of the most common deadly diseases,” according to the film’s narrator. All of these were observational epidemiologic studies (or meta-analyses of observational studies) and carry many limitations that I’ve discussed before (in detail in the five-part Studying Studies series), with the healthy user effect as one of the most important.

Why are people reportedly healthier on a vegetarian diet compared to many non-vegetarians? Is it exclusively because these people eat fewer animals? Imagine a representative survey of adults in the U.S. collecting health habits of these individuals that included the following item in it for people that follow a vegan diet.

Select any of the reasons below why you are a vegan:
⃞       To reduce the impact of my food on the environment
⃞       To eat a healthier diet for my personal health
⃞       To reduce the suffering of animals

How many respondents would not check the “health” box? I suspect the proportion would be vanishingly small. In other words, they’re conscious about their health and they’re engaging in a challenging behavior—avoiding the consumption of animals—they think will improve it. Think about how health-conscious individuals compared on this survey to individuals in the U.S. who eat the Standard American Diet (SAD), a survey that also gathers information on physical activity, access to healthcare, cigarette smoking, vegetable consumption, fruit consumption, vitamin consumption, annual physical exam attendance, sleep habits, meditation, alcohol consumption, socioeconomic status, prescription drug adherence, shift work, and community ties. Think about how anyone following any particular diet that they think is healthy—Atkins, Weight Watchers, keto, Mediterranean, Jenny Craig, paleo, etc.—compare to people eating the SAD.

People who are health conscious are different from people who are not in many different ways. This is the so-called healthy user effect, in a nutshell. I would be hard-pressed to think of a situation in which there’s more potential for a healthy user bias (covered in more detail in Studying Studies: Part III) than comparing a group of people who adhere to a particular diet for health reasons and comparing them to people who unconsciously eat the SAD. When we observe people who consciously adhere to a particular diet, we also see accepted healthy behaviors increase and unhealthy behaviors decrease. It’s not just the diet in these people that is healthier. This shows up again and again (and again) in observational studies.

For example, one such study flashed on the screen was of the diet of Seventh-Day Adventists (SDAs) and their risk of colon cancer. A large proportion (about 30%, based on the reported person-years in the study) of SDAs adhere to a church-recommended vegetarian diet. According to a self-reported questionnaire, the vegetarians not only eliminated meat from their diet, less than 1% of them currently smoked cigarettes (compared to 7% in non-vegetarians), 12% of them had ever smoked in their lifetime (compared to 28% in non-vegetarians) less than 1% of them drank alcohol (compared to 9% in non-vegetarians), and they were more physically active (though not statistically significant) than SDAs that ate meat one or more times per week. There were other differences, some noted in the study, including lower aspirin use in the vegetarians (13% compared to 29%), higher age (54) at baseline (compared to 52 in non-vegetarians, though not statistically significant), and more females (61% compared to 45%, though not statistically significant) and almost assuredly others that weren’t accounted for by the investigators.

The investigators tried to adjust for these differences, but the problem is that this is not only hard to do, there are also other ways that these two groups are different that were not considered. (Both of these problems fall under the heading of residual confounding.) After a six-year follow-up, they found a statistically significant positive association with meat intake and the incidence of colon cancer, with a risk ratio of 1.85.1“[M]ost epidemiologists interviewed by Science said they would not take seriously a single study reporting a new potential cause of cancer unless it reported that exposure to the agent in question increased a person’s risk by at least a factor of 3—which is to say it carries a risk ratio of 3,” writes Gary Taubes in his 1995 article. “Even then, they say, skepticism is in order unless the study was very large and extremely well done and biological data to support the hypothesized link. Sandler Greenland, a University of California, Los Angeles, epidemiologist, says a study reporting a twofold increased risk might then be worth taking seriously—‘but not that seriously.’”

Remember, you should always ask, what are the associated absolute risks? In this case, I calculated (it was not reported in the study) the associated (and unadjusted) six-year risk of colon cancer to be approximately 0.38% and 0.54% for vegetarians and non-vegetarians, respectively. Whether this associated 0.16% difference over six years is attributable to the consumption or avoidance of meat is highly debatable.2Interestingly, the unadjusted absolute differences reveals an associated relative risk increase of 42%, while the reported 85% increase, see 1.85 above, came after adjustment. If the vegetarians were engaging in more accepted healthy behaviors, and fewer unhealthy ones, we would expect the association to get smaller after adjustment, not larger, as was reported. However, also take into account that non-vegetarians were two years younger at baseline. To give you an idea of the potential difference in risk based on age, the 5-year absolute risk difference of developing colon cancer at age 54 compared to 52 is an 0.1% increase in men [0.3% versus 0.4%], as well as an 0.1% increase in women [0.2% versus 0.3%] according to a calculator provided by the National Cancer Institute. What’s less highly debatable is how small the “effect” is, in absolute terms.

The sooner we all can move away from using observational epidemiology like this as a palette to paint our preconceptions with the better. Yes, observational epidemiology helped determine that cigarette smoking is a cause of lung cancer, for example. Contaminated water and cholera. Scrotal cancer and chimney sweeps. I can assure you that those studies were not reporting associated relative risk ratios less than two and absolute risk increases of less than two-tenths of one percent. (For example, the reported relative risk of lung cancer in current smokers of more than 1.5 packs of cigarettes a day was 111.3 and 108.6 in men and women, respectively—over a 10,000% relative risk increase.)  Perhaps most important (other than experiment) of Bradford-Hill’s “nine different viewpoints from all of which we should study association before we cry causation” is the strength of the association.

With such small associations between the consumption of meat and chronic diseases, combined with the high probability of confounding that should strengthen the association, we may be looking at a contrapositive case: If observational epidemiologic study after study either shows a small association, no association, or a negative association, it’s possible to read through the same observational studies most investigators and journalists use to implicate the consumption of red meat and increased risk for colon cancer for example, and conclude that since the observed associations are very small, the risk of confounding very high, the associated absolute differences (which are barely reported) minuscule, and these studies cannot establish cause and effect, that it’s more likely that meat does not cause colon cancer. In other words, a lack of association is evidence for a lack of causation. (For more of my thoughts on the issue of red meat causing cancer, check out my post, “Is red meat killing us?”)

My problem with this film is with its mode of inquiry, not the diet it espouses, per se. Let me state that another way. I’m not against a plant-based diet. I’m against misleading uses of subpar data and speaking with absolute certainty when a bit of humility and nuance should be the standard. The fact is that virtually any diet is better than the SAD from a health perspective. I’m sure we’d see associated improvements with any of the 47 diets listed on the U.S. News & World Report website if people consciously switched to one of these diets from the SAD. The more insidious problem is the healthy user effect. There are many variables that can and do change that could explain the small associations in these studies between meat or vegetable consumption and disease that have nothing to do with the meat or vegetable, making it virtually impossible to establish cause and effect.


– Peter


List of studies

1990 New York Times headline: “Major Study Links Animal Fat to Cancer of Colon”; online headline: “Animal Fat is Tied to Colon Cancer”*
* Related 1990 study: “Relation of Meat, Fat, and Fiber Intake to the Risk of Colon Cancer in a Prospective Study among Women”
1995 New York Times headline: “Health Cost of Meat Diet Is Billions, Study Says”†
† Related 1995 study: “The medical costs attributable to meat consumption”
1998 study: “Dietary risk factors for colon cancer in a low-risk population”
1999 study: “The Oxford Vegetarian Study: an overview”
2001 study: “A prospective study on intake of animal products and risk of prostate cancer”
2009 study: “Meat intake and mortality: a prospective study of over half a million people”
2010 study: “Dietary protein and risk of ischemic heart disease in middle-aged men”
2013 study: “Egg consumption and risk of cardiovascular diseases and diabetes: a meta-analysis”
2014 study: “Low Protein Intake is Associated with a Major Reduction in IGF-1, Cancer, and Overall Mortality in the 65 and Younger but Not Older Population”
2014 study: “Milk intake and risk of mortality and fractures in women and men: cohort studies”
2015 New York Times headline: “Report Links Risks of Some Cancers to Consumption of Processed or Red Meat”; online headline: “Meat Is Linked to Higher Cancer Risk, W.H.O. Report Finds”††
†† Related 2018 study: “IARC Monographs evaluate consumption of red meat and processed meat”
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  1. I read the posts of some here and, yes, about the post-blood test results, Peter needs to reply on them. I got persuaded to follow eating plant-based foods because of my constant fatigue and slow recovery from exercise. After following for less than a month, fatigue gone, and I was able to improve in my physical fitness reps and sets in the same period of time. I can’t forget that meat has something to do with inflammatory cells in our bodies, which is not good, of course. So, I am certainly experiencing better results with no change whatsoever in my lifestyle except for the diet. Pretty conclusive to me. And pretty scientific also on a cellular level. Not convinced by Peter Attia’s analysis and attempt to disprove. I can also see that he is cherry picking on what to argue with about The Game Changers, not tackling about the results of cellular or molecular level tests.

    • Thomas, I think your discounting the fact that its your experience is N of 1. Individual variation is a very real thing. Its possible that animal products have a negative impact on your health, but that doesn’t mean it has to apply to the majority of the population (let alone everyone)

    • It is good to hear you are benefiting from plant-based diet. But your experience is anecdotal and not scientific.

    • Hi Thomas – I’ve had exactly the same experience as you and this is why I’ve switched my diet recently (since the documentary and James Wilks’s subsequent defense on Joe Rogan) to a meat-free whole-plant diet. I’ll revisit in a few weeks. If it works, I’ll stick with it. If it doesn’t, I’ll eliminate certain further foods.

    • Anecdotal evidence is interesting but, by itself, means little. One finds near endless anecdotes of people on a diversity of diets claiming that it reversed or cured all kinds of things. Many of the low-carb, paleo, carnivore, etc advocates, biohackers, doctors, researchers, etc also claim all kinds of things. And, even when research is lacking, they’ll often point to case studies and bloodwork data. It’s useful knowledge for general discussion and can help articulate hypotheses. What it can’t do is proven anything. The point is The Game Changers documentary was taking a fundamentally non-scientific approach.

  2. I watched The Game Changers last night after it came up in discussion at the gym. Seems like there’s a lot of people talking about it!
    I found it interesting whether it was scientific or not but I wanted to hear if there were any counter arguments out there. Hence, I found myself here.
    My thoughts are that your counters don’t seem to be about the film, they seem to be more against the pro vegetarian/vegan vs SAD eater argument.
    Apart from the NYFD, who I would have assumed have to maintain a reasonable level of fitness anyway to carry out their duties, the film featured mainly people who were already athletes to highlight the changes when they moved to a plant based diet, so other changes you correctly point out that apply to SAD eaters when they change diet don’t really apply here.
    The fact that they were fit athletes before they changed to plant based diet and still saw big gains after they changed suggests that there must/might be something to be gained by changing away from meat/dairy?

    • In looking at the physique of some of the firefighters in that film, I don’t think most of them took working out very seriously. I work with many law enforcement officers, firefighters, and other first responders and unfortunately I’d say more than 50 percent of them still consume the standard American diet. Of course a switch to a high vegetable, some fruit, and low glycemic carbohydrate diet is going to effect those gentlemen.

    • Many fit athletes eat horrible diets. Look at all the professional runners, bodybuilders, etc that gorge on refined starches and sugar. And many of the processed foods marketed to athletes (e.g., protein bars) contain such ingredients as industrial seed oils that, in being high in omega-6s, are oxidative, inflammatory, and mutagenic. Some variation of the standard American diet (based on processed foods high in carbs, seed oils, etc) has been fairly common among athletes for a long time and, shockingly, it remains common.

  3. I second Thomas’s experience. I switched to a whole food plant diet three years ago with no other changes and I feel ten years younger. My lipids are now back in the normal range. I sleep better. I feel calmer and more focused. These changes are all due to diet, not other lifestyle changes. (I wasn’t eating the SAD diet before. Just healthy options)
    Also, the impact on the environment from animal foods is enormous. Raising animals for food produces tons of waste, greenhouses gases and takes enormous amounts of land and water. And there’s a reason they made it illegal to take photos of the conditions animals live in before they’re slaughtered. It ain’t pretty.

  4. What about essential nutrients (vitamins and minerals)? I believe most people aren’t meeting recommended requirements on many vitamins and minerals and there are stats on this. The standard recommendation is to get this stuff from diet and not multivitamins.

    We know what nutrients the body absolutely needs. So eating food that has those nutrients and getting blood tests to check that it’s getting absorbed seems to me like a reason to believe that the science on nutrition is converging.

  5. It seems a few anti-meat, plant-only warriors armed with anecdotal “I’ve switched to plant only diet and I feel better” “evidences”, or quoting from anti-credentials, self-styled anonymous (rather conveniently! ) “expert” from the internet who claims (again rather conveniently anonymously) to be in possession of the ultimate unrefutable truth that established lipidologists who have laboured decades in their specific field don’t have a clue about, are rather triggered by this blog post.

  6. I watched Game changers and very much enjoyed it for what it is – a movie. Yes, it’s about the benefits of a plant based diet and it has some “science” in it, but essentially it’s just a movie aimed at ordinary people who are looking for inspiration to get healthier. I don’t understand why would anyone go out of their way to discredit a movie that promotes healthy eating, unless they had some sort of agenda maybe.

    And since anecdotal evidence is all the rage here’s mine:

    I changed to a whole food plant based (WFPB) diet about 2 months ago to see if it will help alleviate the intense pain I got from Ankylosing Spondylitis (AS). My diet up until then consisted of lots of fruit & veg, a bit of meat (mostly chicken), free range eggs and yummy cheeses. My sugar consumption was minimal and I was exercising 4-5 days a week. Sounds healthy right?

    That was until the pain around my shoulders, chest and hips got so bad that I could no longer exercise. AS drugs are quite evil so instead decided to go WFPB cold turkey. Now this is the cray cray part… The pain was pretty much gone after 10 days. 2 Months in I’m back on the ice playing hockey twice a week and doing off ice training 2-3 times a week. BTW, I’m 47.

    I’m not sponsored by anyone, I’m not selling anything, I’m not an MD and I’m not trying to tell you what to do. I’m just sharing my experience because it might help someone else who’s also in pain.

    • There was an agenda – the documentary was made by someone who owns a vegan protein company. The experts on the documentary have books to sell and diet plans to promote. There’s nothing wrong with people trying a variety of diets to find something that works for them, and I support and admire vegans who choose to avoid animal products for health and environmental reasons. But this film was absolutely propaganda with an agenda.

  7. …and, yes, you can be scientific and anecdotal. I’m astonished about the ignorant pretense that only double-blind studies are to be taken as “scientific”. Some of them are. Some of them are not. That’s why you combine information about validated putative mechanisms of action with observation (including so-called anecdotes, if that’s how you’d like to denigrate your own experience.)

  8. Wow, I am part of the vanishingly small number of people who avoid meat and dairy just for the non-health related reasons!

    • @Gerald – I must admit I have more respect for ethical or religious arguments for meat abstention. My oldest brother became a vegetarian when he joined the Hari Krishnas. It was never about health for him and he is open about his willingness to sacrifice his health for what he considers morally right and good.

      That is a personal choice and he is being honest about it. It’s the dishonesty of non-scientific and pseudo-scientific arguments for improved health that are the problem. Still, even the ethical and religious arguments have to be supported by scientific evidence.

      That is the tricky part as it’s not as straightforward as some claim. I’m one of those who argues that animal-based diets (even carnivore) is potentially more vegan than veganism, if by vegan we mean harming the fewest lives, and as long as it’s a diet sourced from regenerative farming, pasture-raised, and sustainably wild-caught.

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