A new study of 22 pairs of identical twins found that, compared to their meat-eating sibling, individuals who followed a vegan diet improved cholesterol levels, blood sugar levels and body weight in just eight weeks.
The findings, published on November 30 in JAMA network opened, suggest that anyone – even people who are already relatively healthy – can adopt a vegan diet to improve their long-term health within two months, the authors say.
Researchers specifically set out to recruit “living, breathing, walking” identical twins – and not people with pre-existing risk factors for cardiovascular disease, such as high LDL (bad) cholesterol, being overweight or obese, says senior author Christopher Gardner, PhD, a professor of healthcare. medicine at the Stanford Prevention Research Center in California.
“Yes, some twins were overweight or had high cholesterol, but many were not. They already had normal cholesterol levels. And yet the vegan group lowered their LDL cholesterol by more than 10 percent and lost weight. We were surprised that it happened so quickly and in a group that didn’t really have high LDL cholesterol to begin with,” says Dr. Gardner.
Only 1 percent of Americans report following a vegan diet
A vegan diet excludes all meat (beef, pork, poultry), seafood and fish, and animal products (dairy and eggs).
In the United States, 4 percent of people report being vegetarian and 1 percent vegan, according to a Gallup poll published in August 2023. The research firm found that women, people who describe themselves as politically liberal and people who report earning less than $40,000 a year are all more likely to eat a vegetarian diet.
Twinning made the research unique – and fun for researchers
The study included 22 pairs of identical twins for a total of 44 participants. All were healthy and had no heart disease, according to the Stanford Twin Registry, a database of fraternal and identical twins who have agreed to participate in research studies. In each pair, one twin was assigned a vegan diet, while the other was assigned an omnivore diet (a diet that includes meat, animal products such as eggs and cow’s milk, and vegetables).
The dual aspect of the study was a lot of fun for the researchers, says Dr. Gardner. “It was just so much fun watching them when everyone got together. They had lots of banter, great stories – and they often dressed alike and had the same hairstyles!”
Including identical twins is an important aspect that made this study unique, he says. Most nutrition studies are observational studies, in part because it’s difficult to get people to change the way they eat and stick with it for weeks or months, Gardner says.
For example, most nutrition studies observe the eating habits of vegans, omnivores or pescatarians, and then report which health outcomes the study is trying to isolate, he says. “And the obvious disadvantage is that the vegans were probably different from the omnivores for other reasons as well. Not only do they exhibit behaviors that can influence their risk, but genetic factors also play a role, and this also applies to randomized trials.”
Using identical twins allowed researchers to control genetics and limit the other factors, because twins grow up in the same households and report similar lifestyles.
Both the vegan and omnivore diets were healthy
The vegan diet was completely plant-based and contained no meat or animal products. The omnivore diet included chicken, fish, eggs, cheese, dairy and other animal foods.
Another unique feature of the study was that both diets were generally healthy and contained vegetables, beans, fruits and whole grains and no sugars or refined starches.
“I am against nutritional studies that compare the ‘favorite’ diet with eating a bad diet. That’s easy to beat. We wanted to compare the benefits of a healthy vegan diet versus a healthy omnivore diet as this makes the findings even more compelling,” he says.
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.
There were some benefits to using the meal service, Gardner says. First, researchers could be sure there was no confusion about what could be included in the vegan diet, he says.
“It also gave people in the vegan group a chance to understand what could be included. It is much more than ‘rabbit food’ or a salad with lettuce. It could be a tofu stir-fry with lots of crunchy veggies, a lentil and black bean burger, a Mediterranean salad with lots of beans and nuts – all very filling,” says Gardner.
In total, 21 out of 22 vegan eaters completed the study – further proof of how generalizable and accessible the diet is, he says.
Vegans had greater decreases in cholesterol, fasting blood sugar and weight
Researchers found that the biggest improvements in heart health occurred within the first four weeks of the diet change.
The average baseline LDL-C level was 110.7 milligrams per deciliter (mg/dL) for the vegans and 118.5 mg/dL for the omnivore participants.
At the end of the study, it dropped to 95.5 mg/dl for vegans (a decrease of about 13 percent) and 116.1 mg/dl for omnivores. The optimal healthy LDL-C level is less than 100 mg/dl.
The vegan participants also showed about a 20 percent drop in fasting insulin (higher insulin levels are a risk factor for developing diabetes) and lost an average of 4.2 pounds more than the omnivores. At the start of the trial, participants’ average BMI was 25.9 kg/m2, slightly above the healthy BMI range, which is 18.5 to 24.9 kg/m2, according to the Centers for Disease Control and Prevention ( CDC).
Further analysis of the participants’ biological age (a measure of how old a person is physically and metabolically) revealed that at the end of the eight-week study, the twins who ate the vegan diet were biologically “slightly younger” than their omnivore counterparts. counterparts, Gardner said in a video about the investigation.
“Based on these results and thinking about longevity, most of us would benefit from a more plant-based diet,” he says.
Why Would a Vegan Diet Improve Heart Health?
The vegan participants did the three most important things to improve cardiovascular health, according to Gardner: they cut back on saturated fats, increased dietary fiber and lost weight.
Most Americans eat about half the recommended amount of fiber, Gardner says.
RELATED: 11 Fiber-Rich Foods to Add to Your Diet
Dietary fiber intake is recommended at 14 grams per 1,000 calories of food. For example, at a reference level of 2,000 calories (which is appropriate for some, but not all, people), daily dietary fiber intake should be 28 grams, according to the United States Department of Agriculture (USDA).
These findings support existing evidence that a vegetarian or vegan diet is associated with improvements in cardiovascular and all-cause mortality, according to a review published in February 2023 in the journal International Journal of Environmental Research and Public Health.
Although the exact mechanism behind the benefits is not yet fully understood, it is suspected that the saturated fats in animal meat and products may cause low-grade systemic inflammation that can contribute to heart disease.
Ready to try a Protein Flip?
If you’re not ready to go completely vegan, you can still work toward eating more vegetables and plant-based protein and less meat by trying a “protein flip,” says Gardner.
“Most Americans think that the center of the plate is chicken, beef or pork and that the side dishes that come with it are grains and vegetables. The protein wrap places plants in the center of the plate: the meat is no longer the centerpiece, but rather a flavoring or side dish,” he says.
One way to try this is with a bowl, which is popular in student restaurants or hot bars in supermarkets. “You can build one yourself. So it might contain meat, but it might also contain tempeh or tofu, as well as grains and vegetables,” he says. The protein flip doesn’t cut out the meat completely, but it can help reduce meat consumption, Gardner says.