Are you really what you eat? That’s the crux of a new Netflix hit series. But how accurate is this new docu-series, and what can we learn from it?
Nutrition science is difficult because it’s hard to know how changes in diet independently impact health, or whether other factors like genetics or lifestyle are at play. While researchers are aware of this, and try to account for this in the study design and analysis, it is often a limitation to this kind of research.
There is, however, a way to remove genetics from the equation, and that is by performing research in identical twins. Of course, it’s difficult to study identical twins as they represent a small proportion of the population. But doing so can ensure that health changes from a dietary intervention are completely independent of genetics. This is the defining feature of the study spotlighted in the new Netflix docu-series, You Are What You Eat.
Image source: Netflix.
'You Are What You Eat'
This four-part docu-series followed a study conducted by a respected team of researchers from Stanford University, where identical twins were randomly assigned a healthy vegan diet or a healthy omnivorous diet for eight weeks. While the study included 22 pairs of twins (with 21 pairs completing the study) (1), the docu-series followed four pairs of twins as they navigated the study.
Episode one introduced the (very charismatic!) twins and explained the rationale for the study, before showing the twins undergoing various laboratory tests to measure their health before beginning the study. Episode two showed how the twins navigated the first four weeks of the study—where food was provided to them—whereas episode three showed how the twins navigated the last four weeks of the study, where food was not provided to them. Finally, episode four revealed whether the eight-week dietary intervention impacted the twins’ health.
While the four sets of twins in this series also exercised under the supervision of coaches, the other 17 sets of twins that were not featured in the documentary did not—and the researchers accounted for this in their analysis to try to ensure that this didn’t affect the overall results (1).
The four sets of twins featured in the docu-series. Image source: You Are What You Eat (Netflix).
After eight weeks, the twins eating the healthy vegan diet had lower levels of low-density lipoprotein (LDL) cholesterol, fasting insulin, and a marker of cardiovascular risk known as TMAO (trimethylamine N-oxide). In addition, the vegan diet group experienced favourable changes in their gut microbiome, had a lower ‘biological age’, and seemed to lose more visceral fat—the dangerous kind of fat that surrounds our organs.
On the other hand, the vegan twins seemed to lose more muscle mass over the eight weeks compared to the omnivore twins. Looking at the first published paper from this study (1), the vegan twins reported eating about 200 calories and 30 grams of protein less per day, and lost more body weight, compared to the omnivore twins. It is therefore unsurprising that they lost more muscle. There were no reported differences in brain function between diets, and while both diets improved sexual arousal while watching porn—yes, you read that right—the vegans seemed to improve to a greater extent.
Visual Abstract of the study, showing the main finding that LDL cholesterol was significantly reduced for the vegan twins relative to the omnivore twins (1). This represents a reduction in heart disease risk, as LDL is a causal risk factor for the process of plaque build-up in our arteries known as atherosclerosis (2).
Because a lot of the results from this docu-series have not yet been published as scientific articles, it’s not possible to currently verify the results. However, the first published paper has verified that LDL cholesterol, fasting insulin, and body weight were lowered for the vegan twins relative to the omnivore twins (1). These findings represent a reduced risk of heart disease and metabolic disorders like type 2 diabetes for the vegan twins compared to the omnivore twins.
If you have seen the docu-series, you’ll notice it discussed much more than the twin study. For example, it talked about the environmental issues with animal agriculture, the horrifying conditions of commercial factory farms, the benefits of alternative meat products, and it included various individuals who had no part in the actual study (e.g., vegan politicians, farmers, business owners, etc.). In this way, the docu-series clearly favoured the vegan diet and tried to make the case for going vegan.
While I think that many of these are valid reasons to go vegan, it is unfortunate that the documentary, at times, cherry-picked evidence to promote the health benefits of going vegan and the negative health consequences of eating animal products. For example, they said that cheese is addictive, but didn’t provide any evidence for this claim. In addition, they mentioned that dairy is associated with increased prostate cancer risk—which it is (3)—but did not mention that dairy is also associated with lower colorectal cancer risk (4).
Overall, I found the docu-series to be the most accurate and informative of all the popular documentaries promoting specific diets. However, this is a very low bar, as these documentaries tend to be very biased, and there were definitely questionable claims included in this docu-series as well. In addition, while the vegan twins did better regarding most health markers, there was little discussion of potential drawbacks to a vegan diet (e.g., lower intakes of essential nutrients like protein, vitamin B12, calcium, etc.).
While the vegan twins lost more muscle relative to the omnivore twins in this study, this doesn’t necessarily have to be the case. Read our previous article on this topic to learn more.
This docu-series shed light on a rigorous scientific study of twins, and that was really cool. In addition, it was fascinating to see how the twins navigated the dietary change, and it really underscored how difficult it can be to change your diet (as one of the twins remarked in episode four). What was also interesting was that after the study, the twins seemed to want to eat a more plant-based diet, while not necessarily excluding animal products.
What did you think? Are you interested in going vegan after watching, or would you like to eat more plant-based, but not to the exclusion of all animal products? Whatever the case, a diet rich in plants is good for both your own health and the health of the planet (5).
If you would like some tips to change your dietary behaviour, check out our collection of articles on behaviour change. And if you would like supplemental football training to improve your skills, reach out to our team of expert coaches at [email protected] to get started.
As always, thanks for reading!
Patrick Elliott, BSc, MPH
Health and Nutrition Science Communication Officer at Training121
(1) Landry MJ, Ward CP, Cunanan KM, Durand LR, Perelman D, Robinson JL, Hennings T, Koh L, Dant C, Zeitlin A, Ebel ER, Sonnenburg ED, Sonnenburg JL, Gardner CD. Cardiometabolic Effects of Omnivorous vs Vegan Diets in Identical Twins: A Randomized Clinical Trial. JAMA Netw Open. 2023 Nov 1;6(11):e2344457. Available at: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2812392
(2) Ference BA, Ginsberg HN, Graham I, et al. Low-density lipoproteins cause atherosclerotic cardiovascular disease. 1. Evidence from genetic, epidemiologic, and clinical studies. A consensus statement from the European Atherosclerosis Society Consensus Panel. Eur Heart J. 2017;38(32):2459–72. Available at: https://academic.oup.com/eurheartj/article/38/32/2459/3745109
(3) Aune D, Navarro Rosenblatt DA, Chan DS, Vieira AR, Vieira R, Greenwood DC, Vatten LJ, Norat T. Dairy products, calcium, and prostate cancer risk: a systematic review and meta-analysis of cohort studies. Am J Clin Nutr. 2015 Jan;101(1):87–117. Available at: https://www.sciencedirect.com/science/article/pii/S0002916523272524
(4) Vieira AR, Abar L, Chan DSM, Vingeliene S, Polemiti E, Stevens C, Greenwood D, Norat T. Foods and beverages and colorectal cancer risk: a systematic review and meta-analysis of cohort studies, an update of the evidence of the WCRF-AICR Continuous Update Project. Ann Oncol. 2017 Aug 1;28(8):1788–1802. Available at: https://www.annalsofoncology.org/article/S0923-7534(19)32133-7/fulltext
(5) Springmann M, Wiebe K, Mason-D'Croz D, Sulser TB, Rayner M, Scarborough P. Health and nutritional aspects of sustainable diet strategies and their association with environmental impacts: a global modelling analysis with country-level detail. Lancet Planet Health. 2018 Oct;2(10):e451–61. Available at: https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(18)30206-7/fulltext