NEW YORK, Nov. 30 (UPI) -- A new trial utilizing identical twins suggests that a vegan diet can improve cardiovascular health in as little as eight weeks.
The Stanford Medicine study that compared vegan and omnivore diets was published Thursday in JAMA Network Open.
An omnivore diet includes a variety of meat and dairy products, as well as plant food groups, including fruit, vegetables and grains.
Although it's well-known that reducing meat consumption benefits cardiovascular health, factors such as genetic differences, upbringing and lifestyle choices often affect diet studies.
Researchers were able to control for genetics and limit the other factors because the identical twins were raised in the same households and reported similar lifestyles.
"This adds scientific rigor to the study," senior author Christopher Gardner, a professor of medicine at Stanford Medicine in Palo Alto, Calif., told UPI in a telephone interview.
Identical twins "share more of the same habits than random people," said Gardner, who has a doctorate in nutrition and is the chair of the American Heart Association's nutrition committee. "That was really the unique nature of the study."
Conducted from May to July 2022, the trial involved 22 pairs of identical twins -- 44 healthy participants without cardiovascular disease. They came from the Stanford Twin Registry -- a database of fraternal and identical twins who have consented to participate in research studies.
In the study, one twin from each pair adhered to a vegan diet while the other followed an omnivore diet.
Both diets were healthy, consisting of vegetables, legumes, fruits and whole grains and devoid of sugars and refined starches. The vegan diet was entirely plant-based, excluding meat and animal products such as eggs or milk. The omnivore diet included chicken, fish, eggs, cheese, dairy and other animal-sourced foods.
During the first four weeks, a meal service delivered 21 meals per week -- seven breakfasts, lunches and dinners. For the remaining four weeks, the participants prepared their own meals.
A registered dietitian was on call to offer suggestions and answer questions about the diets during the duration of the study. The participants were interviewed about their dietary intake and kept a log of their food consumption.
Forty-three participants completed the study, which indicates how practical it is to learn how to adopt a healthy diet in four weeks.
Most of the improvement in cardiovascular health occurred over the first four weeks of the dietary change. Participants on a vegan diet had significantly lower low-density lipoprotein cholesterol levels, insulin and body weight than their omnivore counterparts. All of these factors are associated with improved cardiovascular health.
At three time points -- at the trial's start, at four weeks and at eight weeks -- researchers weighed the participants and drew their blood. The average baseline LDL-C level for the vegans was 110.7 mg/dL, while it was 118.5 mg/dL for the omnivores.
It had dropped to 95.5 for vegans and 116.1 for omnivores by the end of the study. The optimal healthy LDL-C level is considered to be below 100.
Vegan participants had about a 20% drop in fasting insulin, which is important because higher insulin level is a risk factor for developing diabetes. The vegans also shed an average of 4.2 more pounds than the omnivores.
Based on these results and with longevity in mind, Gardner said most people would benefit from gravitating toward a more plant-based diet.
Vegan participants (and the omnivores to some extent) took the three most vital steps to improve cardiovascular health: They cut back on saturated fats, increased dietary fiber and lost weight, Gardner said.
"That doesn't mean we think everyone needs to be vegan," he said. "But many people have room to shift some of the meat out of their diet and include more plants. This is supporting the benefits of that kind of shift."
Dr. Shad Marvasti, an integrative medicine physician and director of public health, prevention and health promotion at the University of Arizona College of Medicine-Phoenix, told UPI in a telephone interview that "the findings were significant at eight weeks, which means anyone making dietary changes can experience the benefits right away.
"That's a good take-home point here -- that you don't have to wait years to see the benefits of a good diet, which is remarkable."
The study validates that a plant-based diet not only reduces risk factors associated with cardiovascular disease, but it also enhances overall health, Susan White, a registered dietitian nutritionist at Allina Health Minneapolis Heart Institute, told UPI in a telephone interview.
White recommends adopting meatless meals once or twice a week. In following a healthier diet, even when people do eat meat, "try not to have it as the centerpiece of your plate," she said. Instead, "make the fruits and vegetables the main event and think of meat as a side dish."
The more plant-based options someone chooses, the more strides they will be making toward better cardiovascular health, Dr. Athena Poppas, a professor and chief of the cardiology division at the Warren Alpert Medical School of Brown University in Providence, R.I., told UPI in a telephone interview.
"It's a lot like walking. Even five minutes a day is better than none," Poppas said. "But if you can walk 30 minutes a day, that will be incrementally better. So, something is better than nothing. I think people feel like they have to do all or nothing, and they get frustrated with a diet or exercise plan."