Nutritionists React to 'You Are What You Eat' Series

Netflix documentary series "You Are What You Eat," based on the Stanford Twin experiment, praises a vegan diet and its impact on our health. While plant-based eating patterns have well-established benefits, nutritionists say the documentary may have exaggerated the study's findings.

The documentary, released in early January, follows eight participants of the Stanford Medicine study that made the headlines after being published last December.

The eight-week experiment included 22 pairs of identical twins, all generally healthy and free of cardiovascular disease. One twin from each pair was matched with either a vegan or healthy omnivore diet rich in vegetables, fruits, and whole grains.

The participants on a plant-based diet saw more significant reductions in the "bad" LDL cholesterol and fasting insulin levels and lost more weight than omnivores.

The authors said that the study provides a groundbreaking way to assert that a vegan diet is healthier than the conventional omnivore diet.

However, researchers not involved in the study say the documentary should be taken with a grain of salt.

'A very different picture'

The documentary paints a very different picture than the official scientific publications of the study, says Dr. Pol Grootswagers, an assistant professor at the Wageningen University & Research in the Netherlands.

For instance, the documentary shows results on body composition and biological age, which are not mentioned in any official trial publications.

"While group effects are of interest from a scientific perspective, the Netflix documentary revolves around individual effects, experiences, and anecdotes. These might be fun to listen to, but have almost no scientific relevance as they can be heavily influenced by various confounding factors or coincidental findings," he tells Healthnews.

Moreover, the documentary shows the researchers assessing changes in the gut microbiota and even sexual arousal, although these are not mentioned in the study.

The documentary draws conclusions that are not warranted based on the scientific results, Grootswagers says. He points out that the only statistically significant results are reduced LDL cholesterol and insulin levels and reduced body weight in the vegan diet group.

The findings are important and are generally beneficial for health. However, we have no idea if the reported weight loss is due to fat or lean mass loss since the trial did not measure body composition via DXA scans, contrary to what the Netflix documentary wants the viewer to believe.

Dr. Pol Grootswagers

In her blog post, Abby Langer, a Toronto-based registered dietitian, calls the documentary "an ad for a vegan diet."

She points out questionable claims, such as the American diet being the number one cause of death in the United States. According to the Centers for Disease Control and Prevention, heart disease is the leading cause of death, but an unhealthy diet is only one of the factors contributing to it.

Gunhild A. Stordalen, M.D., the founder and executive chair of EAT, a global platform for food system transformation, says that the documentary excellently highlights the benefits of a plant-rich diet. However, it noticeably leans towards a pro-vegan perspective.

She wrote on Instagram: "Remember, while plant-based alternatives are often eco-friendlier, they aren't always the healthiest option."

What did the study actually find?

Dr. Jacob Mey, an assistant professor at Pennington Biomedical Research Center who has not seen the documentary, says that, in general, a single study rarely proves anything.

However, the Stanford Twin experiment adds strong additional evidence for the benefits of a vegan diet to improve cardiometabolic health for most individuals.

Although it is hard to draw conclusions about the long-term effects of a vegan diet from the eight-week study, Mey says that following it for a more extended period is likely to improve cardiometabolic health measures in people with higher body mass index (BMI) or elevated LDL cholesterol levels.

During the trial, LDL cholesterol levels decreased from an average of 110.7 mg/dL to 95.5 mg/dL among the participants on a vegan diet and from 118.5 mg/dL to 116.1 mg/dL levels among omnivores. These levels fall under the "near optimal/above optimal" category, ranging from 100 to 129 mg/dL.

The vegan participants showed about a 20% drop in fasting insulin. Elevated insulin levels are associated with type 2 diabetes. However, the fasting insulin levels were normal for both groups — an average of 11.4 uIU/mL among the vegans and 14.7 uIU/mL among the omnivores.

"The 20% sounds beneficial, but in reality, it is a meaningless comparison between two perfectly normal values," writes David Lightsey, M.S., nutrition science advisor at Quackwatch.org.

While weight loss was observed for both diets, the vegans shed an average of 4.2 more pounds than the omnivores.

Benefits of a plant-based diet

Although the documentary may contain exaggerated claims, the health benefits of plant-based diets — not necessarily vegan or vegetarian — are well established.

Grootswagers says that a healthy vegan diet may have positive effects on blood lipid levels and possibly lower the risk for type 2 diabetes, cardiovascular disease, and some types of cancer.

Moreover, a vegan diet benefits the planet's health, as it has a lower impact on several environmental measures such as land use and CO2 emission.

Megan Hilbert, M.S., RDN, a nutritionist at Top Nutrition Coaching, says eating completely vegan may not be necessary to lower LDL cholesterol and insulin and reduce weight, as seen in Stanford's Twin experiment.

She says similar effects on metabolic health can be achieved by following a plant-predominant diet filled with healthy fibers that also includes eating lean meats or fish a few times a week and consuming healthy fats like olive oil — for instance, the Mediterranean diet.

What these diets share in common is high amounts of fiber, high-quality nutrition from plants loaded with vitamins, minerals, and phytonutrients, as well as less saturated fat, refined carbs, and ultra-processed foods.

Megan Hilbert, M.S., RDN

In the documentary, Eric Adams, the mayor of New York City, says he reversed his type 2 diabetes without medication by eating a plant-based diet.

While Adams' claims are not followed by a doctor's comment, studies show that replacing animal foods with plant foods leads to cardiometabolic improvements in type 2 diabetes patients and may even help to achieve remission.

Mey says that, in general, a diet has a powerful impact on our health, and changes in the diet can dramatically reduce the risk of developing not only diabetes but also obesity and cardiovascular disease.

He believes one may have a healthy diet with both animal and plant-based foods. They both contain ingredients that are generally not measured but may positively impact health.

For example, phytochemicals in plants may strengthen the immune system, reduce inflammation, and slow the growth of cancer cells.

Mey adds: "Zoochemicals are ingredients only found in animal-based products. One of them, creatine, is found in higher levels in items like steak and could positively affect strength and mobility. So if you don't consume meat, you're no longer getting that specific zoochemical from your diet."

Health risks of a vegan diet

Despite the long list of benefits, Grootswagers says that it is possible to construct a vegan diet that is very unhealthy.

"Lower protein density and lower protein quality of vegan diets can lead to losses in muscle mass – a side-effect to the LDL-lowering that you want to avoid," he says.

Vitamin B12 is hard to get in a vegan diet, as the nutrient is only naturally found in animal products. Therefore, B12 supplementation is essential for vegans, Hilbert says.

She adds, "Studies show that low vitamin B12 is a significant problem in vegans and is linked with neurological issues and hematologic problems."

Moreover, vegans are at risk of inadequate zinc, iron, vitamin D, and omega-3 intake. These deficiencies can contribute to low energy, poor immunity, dermatitis, poor bone mineral density, and even increased anxiety and depression.

What is a healthy diet?

Vegan or not, does a universally healthy diet exist? Mey says the diet should be about making yourself happy and healthy, meaning that a diet should support one's individual goals.

He tells Healthnews: "An elite athlete may focus on eating lots of food for energy and consuming more than usual amounts of protein to support larger lean body mass. That's a very different goal than someone trying to live a long, healthy life."

For those who would like to try different diets, Mey recommends following a plan that was set up by a registered dietitian. If your goal is to lower the bad cholesterol levels, measure them before starting a new diet and after a certain period to see if the diet is working.

Mey adds, "My favorite tip to give everyone is, 'Go out today, pick up a fresh fruit or vegetable, and eat them.' That will send you on the right path."