Eating plant-based might not be at the top of your resolutions list, but according to Netflix’s new series You Are What You Eat: A Twin Experiment, maybe it should be.
The four-part series follows four sets of identical twins through Stanford University’s recent eight-week pilot twin study (1). The study, which was co-led by Stanford’s Matthew Landry, Ph.D., and Catherine Ward, Ph.D., split sets of twins into two different diets: one sibling was put on a vegan diet (no meat, seafood, eggs, or dairy), while the other ate an omnivore diet (including plants, meat, and animal products).
Among all sets of twins, the study suggested a plant-based diet can increase life expectancy, reduce visceral fat, reduce the risk of heart disease, and heighten sex drive in as little as eight weeks.
Here’s everything you need to know about switching to a plant-based diet.
What Did the Research Show?
To get to the bottom of which diet was healthier, the Stanford research team selected 22 pairs of healthy, identical twins (44 participants in total) and matched one twin from each pair with either a vegan or omnivore diet. Both diets were healthy, and intentionally packed with vegetables, legumes, fruits, and whole grains, and void of sugars and refined starches.
The researchers aimed to investigate the impact of the two different diets on cardiovascular health, metabolic status, and the gut microbiome by testing the following before and after the eight-week intervention:
- LDL cholesterol
- Plasma lipids
- Plasma glucose
- Plasma insulin levels
- Serum trimethylamine N-oxide (TMAO) level
- Plasma vitamin B12 level
- Body weight
- Body composition (muscle vs. fat)
- Biological clock
- Sex drive
- Microbiome bacteria
They also tracked subjective outcomes like diet adherence, ease or difficulty in following the diets, participant energy levels, and sense of well-being. The results surprised even the Stanford research team.
After eight weeks, vegan participants saw significant improvements in cardiometabolic health—including significantly lower LDL cholesterol levels (10% lower on average), lower fasting insulin levels (around 20% lower), and more weight loss (4.2 pounds more)—when compared to omnivore participants.
According to the show, the vegan twins also increased their telomere length. Telomere shortening has been linked to age-related diseases including cardiovascular disease and Alzheimer’s (2). They also had more bifidobacteria—good gut bacteria which have been linked to improved health (3)—and a heightened sex drive.
“Based on these results and thinking about longevity, most of us would benefit from going to a more plant-based diet,” says study registered dietitian Christopher Gardner, PhD told Stanford Medicine. Gardner says he’s been “mostly” vegan for over 40 years, and also happens to be the director of the Stanford Plant-Based Diet Initiative (PBDI), which was launched in 2021 with a 5-year grant by the meat-replacement company, Beyond Meat.
Vegan vs. Omnivore Diet
While the vegan diet was the clear winner for improving cardiometabolic health (and potentially increasing life expectancy, gut health, and sex drive), there were advantages and disadvantages to both diets in the show.
Vegans lost more visceral fat
After eight weeks, the vegan twins lost more visceral fat (the particularly harmful layer of fat that accumulates in your mid-section), while the omnivores held onto their visceral fat and/or gained slightly. Plenty of previous studies have linked visceral fat to an increase in cardiometabolic risk and inflammation (4, 5).
The good news: both diet and exercise can effectively reduce visceral fat. One study found that a plant-based diet can reduce both visceral and subcutaneous fat (6). Exercise reduces visceral fat in a dose-dependent manner, meaning the more exercise you do the more fat you lose (7).
Omnivores built and maintained more muscle
With regular strength training, the omnivore twins gained more muscle on average, while the vegans stayed at baseline or lost a little muscle. Lean muscle mass is an indicator of longevity (8). “If you don’t have muscle, you’re unhealthy, regardless of your pants size or scale weight,” the founder of DexaFit, Amy Kutch-Stanberry says on the show.
The study authors note the vegan diet was lower in protein than the omnivore diet, which might be the root of the issue. Recent studies have hounded the importance of protein for maintaining and gaining muscle (9).
Should You Go Vegan?
Maybe. According to You Are What You Eat, eating a plant-based diet may improve cardiometabolic health, help you lose weight, increase your life expectancy, and even boost libido. Plant-based diets are also rich in antioxidants which may help reduce inflammation, and fiber which may boost gut health (10, 11). Plus, according to a study published in The American Journal of Clinical Nutrition, the more plant-forward your diet is the least impact it has on the environment (12).
However, because the vegan diet is often low in protein it can be hard to build and maintain lean muscle. Plant-based diets may also fail to deliver enough vitamin B12, zinc, calcium, iron, and omega-3 fatty acids—which are key for thriving health on all fronts (13, 14).
Plus, although the twins in the study experienced the benefits of going vegan most of them admitted they didn’t plan to stay vegan. According to a Netflix follow-up, most of the twins featured in the You Are What You Eat series are focused on eating more plants and less meat. “What’s more important than going strictly vegan is including more plant-based foods into your diet,” says Gardner.