Eating a more plant-based diet and less meat is good for your cardiovascular health, as many studies have shown. The only drawback has been that these studies have been limited by the possibility that differences in participants' upbringing and lifestyle and genetic differences might have affected the results.

A recent study of the effects of a vegan as opposed to a healthy non-vegan diet on identical twins by researchers from Stanford was able to account for genetics and limit the effect of other factors because the twins had similar lifestyles and grew up in the same households.

Twenty-two pairs of adult identical twins were randomly assigned to follow either a healthy vegan diet or a healthy omnivorous diet for eight weeks, with one twin assigned to each type of diet. “We wanted to compare a vegan diet to a healthy American diet, not a poor American diet,” explained Christopher Gardner, senior author on the study.

All the twins participating in both groups were healthy. “We picked generally healthy people who wouldn't necessarily benefit from a change in diet,” Gardner added. Participants weighed more than 100 pounds, had a body mass index (BMI) of less than 40 kg/m2, low-density lipoprotein cholesterol (LDL-C) of less than 190 mg/dL, and systolic blood pressure of less than 160 mmHg or diastolic blood pressure less than 90 mm Hg.

The study found that a vegan diet could improve cardiovascular health in as little as eight weeks, compared to an omnivorous diet.

“Based on these findings and thinking about longevity, most of us would benefit from going to a more plant-based diet,” Gardner, a professor of medicine at Stanford, told TheDoctor.

After eight weeks, twins randomized to a vegan diet had significant decreases in LDL-C, fasting insulin levels and weight compared to their twins on an omnivorous diet.

The study was done in two four-week phases. During the first four-week phase, all meals were delivered to participants' homes. The meals were developed in collaboration with a nationwide meal delivery service. During the second phase, participants shopped for and prepared their own meals. Following an overnight fast, blood was drawn at three timepoints: baseline, four weeks and eight weeks.

After eight weeks, twins randomized to a vegan diet had significant decreases in LDL-C (about 14 mg/dL), fasting insulin levels (almost 3 µIU/mL) and body weight (almost 2 kg) compared to twins randomized to an omnivorous diet. Lower LDL-C and insulin levels and body weight are associated with better cardiovascular health.

More results about the effects of vegan versus omnivorous diets on biological aging and the gut microbiome are forthcoming. There was simply too much data to include in only one study. “We have a lot more samples banked, including stool samples, so analyzing those samples will add another piece to the story,” Gardner explained. He suggested, for example, that a vegan diet may contribute to other benefits such as increased gut bacteria and reduced telomere loss, which slows aging.

The study is published in JAMA Network Open.