By now, it shouldn’t be a secret to anyone that eating less meat is better for your cardiovascular health. But untangling the complex variables of nutrition is never easy. But in the new study, researchers bypassed that by studying identical twins. By studying twins, the researchers were able to eliminate the genetic variable and limit other health factors (such as what they ate growing up).

The trial was conducted from May 2022 to July 2002. It was an 8-week randomized clinical trial involving 44 participants — 22 pairs of identical twins. Each pair was randomly assigned to either a vegan or an omnivorous diet, providing a unique opportunity to control for genetic and environmental factors that might influence the outcomes​​​​​​.

“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,” said Christopher Gardner, PhD, the Rehnborg Farquhar Professor and a professor of medicine. “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.”

The diet whisperers

Participants received meals from a delivery service for the first four weeks, followed by self-prepared meals for the remaining duration. The diets were designed to be healthy within their respective categories, emphasizing whole grains, vegetables, and fruits while limiting refined grains and added sugars.

Dietary intake was monitored through structured interviews and a nutrition tracking app​​​​​​. Participants also had access to a registered dietitian — a “diet whisperer,” the researchers say. The diet whisperer was available to offer suggestions and answer questions for the duration of the study.

However, the diets themselves were not special. In fact, 43/44 participants stuck with the diet they were assigned to after the study.

“Our study used a generalizable diet that is accessible to anyone, because 21 out of the 22 vegans followed through with the diet,” said Gardner, who is a professor in the Stanford Prevention Research Center. “This suggests that anyone who chooses a vegan diet can improve their long-term health in two months, with the most change seen in the first month.”

Vegans had better cardiovascular health

The researchers weighed participants and ran blood tests three times during the study — when it started, at four weeks, and at 8 weeks.

After just four weeks, participants on a vegan diet had significantly lower levels of low-density lipoprotein cholesterol (LDL-C) levels — the “bad cholesterol” — as well as reduced insulin and body weight.

When the study started, the average LDL-C level was 110.7 mg/dL for vegan diet participants and 118.5 mg/dL for the omnivore diet participants; it dropped to 95.5 for vegans and 116.1 for omnivores by the end of the study. Optimal LDL-C levels are considered to be under 100. The researchers suspect that the difference would have been even greater with participants who were more unhealthy.

The vegan participants also showed a 20% drop in fasting insulin (a risk factor for developing diabetes) and lost 4.2 pounds (1.9 kg) more than the omnivores.

“Based on these results and thinking about longevity, most of us would benefit from going to a more plant-based diet,” Gardner said.

You don’t need to go vegan. Just eat more plants

Of course, a vegan diet can be quite restrictive. Plus, there’s more to overall health than just cardiovascular health. But the important takeaway, says Gardner, is that incorporating more plants into our diet is definitely a good idea.

“A vegan diet can confer additional benefits such as increased gut bacteria and the reduction of telomere loss, which slows aging in the body,” Gardner said. The researcher added that it’s a good idea to look at multicultural foods that are rich in fruits and vegetables.

“What’s more important than going strictly vegan is including more plant-based foods into your diet,” said Gardner, who has been “mostly vegan” for the last 40 years. “Luckily, having fun with vegan multicultural foods like Indian masala, Asian stir-fry and African lentil-based dishes can be a great first step.”

The study was published in JAMA.