The discovery that eating less meat can improve cardiovascular health is not new, but previous studies supporting this idea have often been influenced by confounding factors such as genetics, background and lifestyle. Now, scientists have eliminated many of these variables by comparing a healthy omnivore diet with a healthy vegetarian diet in a study of identical twins.
Stanford University recruited 22 pairs of identical twins who grew up together and reported similar modern lifestyles to conduct an eight-week controlled trial of meal plans in an effort to provide stronger data to support existing evidence.
Christopher Gardner, a professor of medicine at Stanford University, said: "Not only is this study groundbreaking in proving that a vegetarian diet is healthier than a traditional omnivorous diet, but the twins are also very interesting to work with. They dress the same, they talk the same, and there is an air of banter between them that you only get when you spend too much time together."
More than three-quarters of the twins, whose average age was 39.6, were living with their siblings at the time of the study. 69% of participants said they were very similar to their twins.
Over eight weeks, the twins were randomly selected to eat either a healthy plant-based diet or a healthy omnivore diet, and were provided dietitian-designed meals by a meal delivery service for the first month. After this, participants prepare their own meals based on their specific dietary requirements.
Participants will be evaluated before, during, and after the trial, including blood tests, weighings, stool tests, and more. Vegetarians had the greatest change in low-density lipoprotein cholesterol (LDL-C), from 110.7 mg/dL to 95.5 mg/dL (omnivores fell from 118.5 mg/dL to 116.1 mg/dL). The optimal range is below 100 mg/dL.
Notably, the twins in the study generally already had fairly healthy LDL levels, and Gardner expected those with worse baseline measurements to see a larger drop in LDL levels.
Vegetarians also had about a 20 percent drop in fasting insulin and lost an average of 4.2 pounds (1.9 kilograms) more than their meat-eating counterparts.
"Based on these results and thinking about longevity, most of us would benefit from a plant-based diet," Gardner said.
Both diet plans focus on vegetables, legumes, and whole grains while omitting refined sugars and starches. Of course, the plant-based plan omits all animal products, including eggs and milk, while the omnivorous plan includes fish, chicken, eggs, cheese, and dairy products.
At the end of two months, 43 participants had completed the study, which the researchers noted showed how easy it is to learn to cook healthy dishes, which the twins had to learn to cook after the fourth week of delivery, which ended with 21 meals a week.
"Our study used a universal diet that anyone could follow, as 21 out of 22 vegetarians adhered to it," Gardner said. "This suggests that anyone who chooses a vegetarian diet can improve their long-term health within two months, with the greatest changes occurring in the first month."
Interestingly, in a future study, twins on a vegan diet also tested younger, making their biological age younger than their actual age. This proves that a vegetarian diet can bring additional benefits, such as increasing intestinal bacteria and reducing telomere loss, thereby delaying human aging.
While researchers know that one study isn't likely to convince anyone to adopt a plant-based diet full-time (one vegetarian twin said she ate less because she didn't want to eat more whole grains or vegetables), the main takeaway from the study is how effective reducing saturated fat, increasing dietary fiber and losing weight can improve cardiovascular health.
"What's more important than going strictly vegetarian is getting more plant-based foods into your diet," says Gardner, who has been 'basically vegetarian' for 40 years. Fortunately, having fun with vegetarian multicultural foods like Indian masalas, Asian stir-fries and African lentil dishes is a great first step.
The study was published online in the Journal of the American Medical Association.