Identical twins tried plant-based and omnivore diets — the vegans were biologically younger and healthier in just 8 weeks

• Vegan diets may lead to better heart health and slower aging, suggests a new study of twins.
• 22 pairs of twins tried either vegan or omnivore diets to control for factors like genetics.

Sorry, omnivores — vegans have won the latest round in the diet wars, thanks to a head-to-head study using identical twins to directly compare the two styles of eating.

Eating a vegan diet was linked to better heart health, more weight loss, and even signs of slower aging after just eight weeks, according to the research, published November 30 in JAMA Network Open.

Researchers from Stanford University looked at 22 sets of identical twins, healthy adults averaging 40 years old, as they underwent an eight-week diet experiment. One member of each pair of twins was randomly assigned a vegan diet, eating exclusively plant-based foods with no meat, eggs, dairy, or other animal products. The other twin in each pair was assigned an omnivorous diet, including at least one serving of fish, meat or chicken, one egg, and a serving and a half of dairy per day.

Both diets were designed to be nutritionally balanced and full of veggies, beans, and whole grains, without added sugars or other refined carbs. The food was provided at no cost to participants by a meal delivery service for the first four weeks, after which participants prepared their own meals and snacks, with guidance from an on-call dietitian.

At the end of the trial, researchers found that the participants on the vegan diet had lower cholesterol and insulin levels and lost more weight than their meat-eating counterparts.

But "the most interesting part of the study" was that the vegans were also biologically younger based on markers of health, according to Christopher Gardner, senior author of the study and professor of medicine at Stanford.

"Based on these results and thinking about longevity, most of us would benefit from going to a more plant-based diet," he said in a press release.

Biological age — and how to reverse it — is a hot trend in healthcare, but measuring it can be complex and sometimes controversial Business Insider's Hilary Brueck previously reported.

Additional evidence has suggested that plant-based eating habits are linked to healthier aging, and can add years to your life.

While plenty of studies have tried to compare vegan and omnivore diets, other variable can skew the results, such as the fact that vegans may be more health conscious in other ways, or have different socioeconomic backgrounds or resources.

Using twins allowed the study to uniquely account for variables such as genetics and upbringing, invaluable data that also turned out to be fun, Gardner said in a press release.

"Not only did this study provide a groundbreaking way to assert that a vegan diet is healthier than the conventional omnivore diet, but the twins were also a riot to work with," he said. "They dressed the same, they talked the same and they had a banter between them that you could have only if you spent an inordinate amount of time together."

You may not have to go fully vegan for better health

All but one of the vegan twins were able to stick to the diet throughout the study, suggesting it could be an accessible way for people to learn to eat more healthfully, Gardner said in the press release.

Sustainability is key for a healthy diet, since you'll only benefit from an eating plan if you can continue following it long-term, dietitians have previously told Insider.

However, the vegan participants self-reported that they weren't as happy with their food, which could account for the extra weight loss. And a follow-up interview at Stanford found that not all of them opted to remain vegan after the study — one mentioned she transitioned to vegetarianism instead.

As a result, trying to eat more beans, whole grains, veggies, and nuts could pay off for your long-term health even if you don't swear off animal-based foods completely, according to Gardner, who said he has been "mostly vegan" for four decades.

"What's more important than going strictly vegan is including more plant-based foods into your diet," he said in the press release.