Switching to a vegan diet may improve heart health in just eight weeks, according to a twin study by Stanford University researchers.
Only 1% of Americans report being vegan, despite research showing the health benefits of plant-based diets. The latest study, published in the JAMA Network, suggests that a vegan diet can effectively reduce "bad cholesterol" and insulin levels and lead to weight loss.
The trial included 22 pairs of identical twins — a total of 44 adults — without cardiovascular disease. One twin from each pair was matched with either a vegan or omnivore diet.
The vegan diet was entirely plant-based and did not include meat or other animal products, such as eggs or milk. The participants on the omnivore diet consumed chicken, fish, eggs, dairy products, and other animal-sourced foods.
Overall, both diets were healthy, as they were rich in vegetables, legumes, fruits, and whole grains and free of sugars and refined starches.
During the first four weeks, the participants were delivered three meals a day. For the remaining four weeks, they prepared their own meals.
All but one participant on a vegan diet completed the study, suggesting that a healthy diet is accessible to everyone and it is possible to learn how to prepare healthy meals in four weeks.
Lower levels of 'bad cholesterol'
Researchers weighed the participants and drew their blood at the beginning of the trial, at four weeks, and at eight weeks to measure their low-density lipoprotein cholesterol (LDL-C or "bad cholesterol") and insulin levels.
The improvements were most significant within the first four weeks after the diet change and more pronounced among those on a vegan diet.
The participants eating a vegan diet had significantly lower LDL-C cholesterol levels: it decreased from an average of 110.7 mg/dL at the beginning of the study to 95.5 after eight weeks. Among omnivores, the levels of LDL-C cholesterol dropped from 118.5 mg/dL to 116.1 mg/dL.
The optimal healthy LDL-C level is less than 100. High bad cholesterol is associated with an increased risk of narrowing of the arteries, heart attack, and stroke.
The vegan participants also saw approximately a 20% drop in fasting insulin — a higher insulin level is a risk factor for developing diabetes. They also lost an average of 4.2 more pounds than the omnivores.
"A vegan diet can confer additional benefits such as increased gut bacteria and the reduction of telomere loss, which slows aging in the body," Christopher Gardner, a professor at the Stanford Prevention Research Center, said in a statement.
Most importantly, both vegans and omnivores in the study reduced the intake of saturated fats, increased dietary fiber, and lost weight, all of which are crucial for heart health.
Concerns over vitamin B12 intake
Despite improvements in body weight, cholesterol, and insulin levels, the vegan participants reported lower dietary satisfaction and had a lower protein intake. Protein is crucial to building and repairing muscles and bones and plays a role in making hormones and enzymes.
Moreover, the vegans in the trial had a lower intake of vitamin B12, an essential nutrient not found in plants. Vegans and vegetarians are more likely to experience vitamin B12 deficiency, which may lead to anemia and nervous system damage.
The symptoms of B12 deficiency may include depression, memory impairment, tiredness, and muscle weakness.
Vegans and vegetarians may receive vitamin B12 from foods fortified with it, such as plant milks, soy products, and supplements.
Because the study population was small and generally healthy, the findings may not be generalized to other populations. It is also difficult to tell how sustainable these diets are in the long term because there was no follow-up after the eight-week period.
Although a vegan diet may not be for everyone, the health benefits of consuming more plant-based foods are well-established.
- JAMA Network. Cardiometabolic Effects of Omnivorous vs Vegan Diets in Identical Twins.
- Stanford Medicine. Twin research indicates that a vegan diet improves cardiovascular health.
- Gallup. In U.S., 4% Identify as Vegetarian, 1% as Vegan.
- National Library of Medicine. The importance of vitamin B12 for individuals choosing plant-based diets.
- Vegan Society. What Every Vegan Should Know About Vitamin B12.