Review of the Netflix documentary “You Are What You Eat: A Twin Experiment”

Have you seen the Netflix documentary on the study conducted by a set of twins on diet and health? Several individuals have been asking me since the famous documentary aired in January about the impact of a transition to an exclusively plant-based diet. As a nutritionist, I looked into the subject. What is the real story behind this documentary? Are plant-based diets and their potential health benefits as miraculous as they’re made out to be? Let’s explore the question a little by reviewing what the documentary says.

The Netflix documentary and the twins’ study

The short four-part series makes the case for the move to a plant-based diet, on the one hand for its human health benefits and, on the other, for its environmental advantages. A team of Californian researchers report on the findings of a study carried out on 21 pairs of identical adult twins. One twin was randomly assigned to a healthy omnivorous diet (including products of both animal and plant origin), while his twin was offered an exclusively vegan menu (completely free of animal products, excluding meat, poultry, fish/seafood, eggs, dairy products, and honey).

The study was conducted in two phases. The first involved participants having healthy meals delivered from home, followed by a second phase in which participants were autonomous in the way they chose and cooked their food. This enabled the researchers to evaluate the changes in a more controlled context, and then in a “real-life” context where each participant chooses and cooks his or her own food.

Several themes including cardiovascular health, weight/body composition, gut microbiota and longevity were evaluated during the study. At the end of the documentary, the verdict seems unanimous. It’s the overwhelming victory of the plant-based diet on most issues.

The effect of sensationalism

Those who have seen documentaries the likes of “The Game Changers”, “Cowspiracy” and “Seaspiracy” will understand the warning about the sensationalist effect often used in this kind of wide-ranging documentary. Frightening analogies, shocking statistics, and grandiose testimonials from a host of well-known personalities are all part of the package. This documentary is no exception. Scientists, doctors, biologists, animal rights activists, top chefs and the mayor of New York all have something to say to convince us. Does this mean that what they say is fraudulent and completely false? Not necessarily! But are they sometimes amplified to convince us even more? Sometimes, yes! Here’s an example:

• Statistic mentioned in the documentary: the animal agriculture sector contributes to 20% of total greenhouse gas emissions worldwide, which is more than the 14.5% attributed to the transport sector, all modes of transport combined.
• Reworded without the “amplified” effect: The agriculture sector (including land use for all crops, deforestation, livestock) contributes 18.5% of global greenhouse gas emissions. Within this 18.5%, livestock accounts for 31%. See the nuance?

The conclusion to be drawn here: yes, the meat industry contributes significantly to air pollution, and we would benefit from reducing our meat consumption, but BE CAREFUL with the interpretation of figures that seek to impress.

The effects of scare tactics

Another familiar tactic in documentaries of this kind is to use scare tactics to make the story more convincing. A few examples to highlight here:

• Farmed salmon contaminated with bacteria, viruses, parasites, heavy metals and microplastics.
• The statistic that 20% of poultry sold is contaminated with E. coli bacteria, which could contaminate your entire kitchen.

Once again, the idea is not to refute these claims completely, but rather to bring more nuance to the statements, which are brought into a frightening perspective to better persuade. You won’t be poisoned for sure if you eat salmon once a week. However, the idea of encouraging critical thinking on the impact of mass animal/marine farming and its impact on the health/diversity of ecosystems is an important one.

Study findings – Plant-based nutrition and its potential health benefits!

Returning to the twins’ study and its results, what are the relevant and statistically significant findings worth highlighting? Here are a few noteworthy points:

• Twins who followed an exclusively vegan diet for 8 weeks saw:
• Their LDL (“bad”) cholesterol levels were reduced by 10% on average, compared with the omnivorous group for whom this parameter remained unchanged. This result corroborates other high-level studies conducted in the past which have produced similar results, suggesting that adopting a vegan diet is the best way to reduce cholesterol levels and developing cardiovascular diseases.
• Greater weight loss (7.5 lb) compared with the omnivorous group (1.1 lb), possibly because the plant-based diet was richer in dietary fibre and less dense in calories, according to data collected from customers.
• Reduced blood sugar and insulin levels compared to the omnivore group, probably secondary to the greater weight loss and higher fiber intake.

Study methodology: strengths and weaknesses

The study we carried out has its advantages, but also limitations that are worth mentioning and considering when interpreting the results.

Advantages

• The pairs of identical twins recruited for the study made it possible to control the genetic factor in a research context, which is usually difficult to control.
• Firstly, having two phases in the study facilitated adherence to dietary changes (meals provided in phase one), and then to take into account the “real-life” context later on when participants prepared their meals independently in phase two.

Limitations

• The short-term nature of the study makes it impossible to apply the results over a period longer than 8 weeks.
• The study group consisted of healthy adults. The results are therefore not applicable to a population with health issues (e.g. diabetes, heart disease).
• Two potential conflicts of interest were mentioned by the study’s authors, which could lead us to believe that a bias in favor of plant-based diets had been taken in advance.

In a nutshell…

After watching the Netflix documentary, if you’re interested in learning more about plant-based eating or are looking to reduce your consumption of animal products, here are five tips to keep in mind:

1. Do it at your own pace! The positive impacts on health/ecological footprint will be present even if you don’t make a drastic or complete change all at once and will be more sustainable over the long term!
2. Moving to a meat-free diet is not necessarily synonymous with “health”. Bear in mind that regular, predominant consumption of ultra-processed products, whether animal-based or not, will not bring the hoped-for health benefits.
3. Research topics you are unfamiliar with (cooking with plant-based foods, vegan nutrition with a nutritionist, reading and documentaries on the environmental impact of a diet free of animal products, etc.).
4. Develop your critical thinking skills. Learn to question what you hear and read and identify reliable sources of information.
5. Keep an open mind. Discover plant-based foods even if you want to keep animal products in your diet.

Featured photo © Netflix

References

• Gehring, J., Touvier, M., Baudry, J., Julia, C., Buscail, C., Srour, B., … & Allès, B. (2021). Consumption of ultra-processed foods by pesco-vegetarians, vegetarians, and vegans: associations with duration and age at diet initiation. The Journal of nutrition, 151(1), 120-131.
• Jenkins, D. J., Kendall, C. W., Marchie, A., Jenkins, A. L., Connelly, P. W., Jones, P. J., & Vuksan, V. (2003). The Garden of Eden—plant-based diets, the genetic drive to conserve cholesterol and its implications for heart disease in the 21st century. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 136(1), 141-151.
• Landry, M. J., Ward, C. P., Cunanan, K. M., Durand, L. R., Perelman, D., Robinson, J. L., … & Gardner, C. D. (2023). Cardiometabolic Effects of Omnivorous vs Vegan Diets in Identical Twins: A Randomized Clinical Trial. JAMA Network Open, 6(11), e2344457-e2344457.
• Mayra, S., Ugarte, N., & Johnston, C. S. (2019). Health biomarkers in adults are more closely linked to diet quality attributes than to plant-based diet categorization. Nutrients, 11(6), 1427.
• Ritchie, H., & Roser, M. (2023). Sector by sector: where do global greenhouse gas emissions come from? Our World in data.
• Sherwood-Martin, H. (2024). You Are What You Eat: a Twin Experiment. The Lancet Gastroenterology & Hepatology, 9(4), 297.
• Stern, N. H. (2007). The economics of climate change: the Stern review. Cambridge University press.
• Wang, F., Zheng, J., Yang, B., Jiang, J., Fu, Y., & Li, D. (2015). Effects of vegetarian diets on blood lipids: a systematic review and meta‐analysis of randomized controlled trials. Journal of the American Heart Association, 4(10), e002408.

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