In a recent study published in the journal JAMA Network Open, researchers in the United States compared the cardiometabolic impact of vegan diets versus omnivorous diets after eight weeks of intervention among adult identical twins.
Study: Cardiometabolic Effects of Omnivorous vs Vegan Diets in Identical Twins. Image Credit: Foxys Forest Manufacture / Shutterstock
Plant-origin diets are becoming more popular due to their low environmental impact and health benefits. Non-communicable diseases and climatic change are major worldwide health issues, and eating more vegetables and less meat can optimize health and the environment. Vegan diets often have a lower energy density but a greater concentration of phytonutrients, fiber, minerals, and vitamins.
According to previous observational and interventional studies, veganism is associated with enhanced cardiovascular wellness and a lower cardiovascular disease risk due to a higher intake of fruits, vegetables, whole grains, legumes, seeds, and nuts. Vegan diets, on the other hand, might restrict a few nutrients like calcium, iron, and vitamin B12. Most studies on vegan diets are epidemiologic, with only a few clinical investigations recorded.
About the study
In the present population-based, single-center randomized controlled trial (RCT), researchers comparatively evaluated the cardiometabolic effects of vegan and omnivorous diets in identical twins.
The parallel-group, open-label RCT included 22 twin pairs (n=44) randomized to the vegan or omnivorous diet group for eight weeks (one twin per diet). All participants were exposed to fruits, vegetables, whole grains, legumes, seeds, and nuts, limiting the exposure to refined grains and added sugar. The participants were recruited from the Stanford Twin Registry between March 28 and May 5, 2022. Data were obtained through July 20, 2022.
The team provided diet-specific meals through national meal delivery services for four weeks, following which the study participants self-prepared their meals. The meals comprised minimally processed foods, protein, vegetables, starch, and healthy fat, variety in all food groups, and catered to individual requirements and preferences. All participants were advised to eat until satisfaction with no calorie restriction.
The primary data comprised three 24-hour diet recalls (one weekend and two weekdays); registered dieticians administered telephonic structured interviews to obtain detailed food and drink intake data within a week of each timepoint (study initiation, fourth week, and eighth week). The participants provided secondary data by recording their food intakes in the Cronometer application; health educators used secondary data to guide the participants in real-time. All participants provided blood and stool samples. The primary study outcome was altered low-density lipoprotein cholesterol (LDL-C) concentration in serum eight weeks post-intervention.
Secondary study outcomes included alterations in cardiometabolic parameters (blood glucose, insulin, lipid, and trimethylamine N-oxide (TMAO) levels), serum vitamin B12 levels, and weight. Exploratory measures included dietary adherence, difficulty or ease in adhering to the diets, energy levels of the participants, and a sense of well-being.
Changes in the intestinal microbiome, inflammatory biomarkers, and metabolites were also assessed. Linear mixed modeling was performed for the analysis. The team excluded individuals weighing ≤45 kg with a body mass index (BMI) of ≥40, LDL-C ≥190 mg/dL, systolic-type blood pressure ≥160 mm of Hg, diastolic-type blood pressure ≥90 mm of Hg, and those who were pregnant.
Among the participants, 77% (n=34) were female, 73% (n=32) were white, and 79% (n=33) lived with their twin; the mean values for participant age and BMI were 40 years and 26, respectively. Both groups consumed fewer calories in the two four-week phases (food delivery and self-prepared) than at baseline.
After eight weeks, compared to twins allocated to the omnivorous diet group, the vegan diet group twins showed significantly reduced LDL-C (14 mg/dL), fasting insulin (3.0 μIU/mL), and weight (2.0 kg). In addition, vegans showed a greater but non-significant decrease in serum high-density lipoprotein cholesterol (HDL-C), vitamin B12, triglycerides, TMAO, and glucose levels after eight weeks of intervention compared with omnivores.
In the sensitivity analyses, after eliminating outliers, vegans showed a mean reduction of 2.1 μM in the difference of TMAO from baseline to eight weeks compared to omnivores. The exploratory analysis findings indicated that omnivores had nominally higher dietary satisfaction in the fourth and eighth weeks than vegans.
Overall, the study findings showed that the vegan diet improved cardiometabolic profiles compared to the omnivore diet, with decreased LDL-C and insulin levels. Vegans consume less protein, have poorer dietary satisfaction, and have higher vegetable and iron consumption. They do, however, consume less vitamin B12. Clinicians should consider veganism a healthy alternative for patients, and long-term vegans are frequently urged to take a cyanocobalamin supplement. More studies on TMAO risk factors and patient preferences are required.