Beneficial cardiometabolic effects of the vegan diet vs. an omnivorous diet

Plant-based diets have gained popularity in recent years, both for reducing environmental impact and for the health benefits they provide, compared to an omnivorous diet. Plant-based diets are very varied, which encourages reducing the consumption of foods of animal origin. Numerous populational and intervention studies indicate that the vegetarian diet is associated with better cardiovascular health and a lower risk of cardiovascular disease. Health benefits have been attributed to high daily consumption of vegetables and fruits, legumes, whole grains and nuts compared to other diets (see our articles on the subject here and here). Foods consumed by vegans are low in energy density, high in fibre, vitamins, minerals, and phytonutrients compared to those consumed in other diets. However, the vegan diet can be deficient in some elements, such as vitamin B12. In addition, a poorly formulated vegan diet that contains mainly poor quality plant foods, refined sugars, etc. (processed and ultra-processed products) will not deliver the benefits of a healthy, balanced vegan diet.

One of the best ways to establish whether one diet offers benefits over another is to compare them in an intervention study. This is what American researchers did in an 8-week randomized, controlled clinical trial involving 22 pairs of identical twins (44 participants). One twin in each pair was randomly assigned to follow a vegan diet and the other a high-quality omnivorous diet. For the first 4 weeks, participants received meals prepared by a specialized company and delivered to their homes. During the following 4 weeks, the participants prepared their own meals and snacks. The first 4 weeks with home delivery of meals made it easier for participants to adhere to the diet.

After the 8 weeks of the study, the participants who followed the vegan diet saw their blood LDL cholesterol significantly decrease by 0.40 mmol/L (–14%), their fasting insulin level decrease by 2.2 µIU/mL, and they lost 1.4 kg of body weight on average. No significant changes in the levels of these cardiometabolic risk factors were measured in participants who followed the omnivorous diet after the 8 weeks of the study.

Participants assigned to the vegan diet ingested less protein (as a percentage of total calories), had lower levels of satisfaction as well as a lower intake of dietary cholesterol, but they ate more plant foods and had higher iron intakes. Although they had a lower vitamin B12 intake than the omnivore group, participants in the vegan group did not have significantly lower blood levels of vitamin B12 after 8 weeks, probably because of reserves stored in the liver. Long-term vegans are generally encouraged to take cyanocobalamin (vitamin B12) supplements (see our article on the subject).

Several studies have already shown that a vegan diet can improve cardiometabolic health. A unique feature of the study discussed here is that it was conducted in identical twins, making it possible to control for genetic and environmental factors that can have a significant impact on health, including body weight, cardiovascular health, and metabolism. Since identical twins have a virtually identical genome (DNA) and have much in common (same sex and age, education, childhood environment, similar exposure to other factors), the favourable health effects of the vegan diet observed in this study can be attributed largely to the diet itself.

The researchers tested other markers such as HDL cholesterol, triglycerides, trimethylamine-N-oxide (TMAO), glucose, and insulin, but no significant changes in the levels of these markers were observed in the participants of the two groups. The authors point out that two factors could have limited the magnitude of the differences between the two groups: 1) participants in both groups (vegans and omnivores) were assigned to eat good quality foods, in this case food of better quality than that usually consumed before the start of the study. Even the omnivorous participants improved the quality of their diet during the duration of the intervention (e.g., more vegetables and whole grains, less added sugars and refined grains); 2) participants had an average LDL cholesterol level that was not high (2.97 mmol/L), leaving little room for a decrease. Nevertheless, significant improvements were observed for three risk factors (LDL cholesterol, insulin, body weight) among the vegan participants during a relatively short 8-week intervention.

In summary, this new high-quality intervention study suggests that a plant-based diet offers a significant cardiometabolic benefit compared to an omnivorous diet.