The trial period was comprised of two four-week periods; during the first 4 weeks, participants had three meals per day provided for them, intended also to serve as a guide for the second 4 weeks during which they’d provide for themselves. Both diets were intended to provide healthy choices, emphasizing variety, minimally processed foods, and a balance of vegetables, protein, starch, and healthy fats, without restricting calories. Both groups improved their diet quality from baseline during the study period, marked by reductions in added sugar, refined grains, and increased vegetable intake.
After 8 weeks, the twins following the vegan diet had a significant reduction in the primary outcome, with LDL-C levels lowered by a mean of 13.9mg/dL compared to their siblings following the omnivorous diet. Additionally, twins on the vegan diet also had a significant reduction in fasting insulin (−2.9 μIU/mL) and body weight (−1.9 kg) compared to twins on the omnivorous diet. It should be noted that this was a fairly healthy study group. For example, the baseline LDL-C was 114 mg/dL, a fairly low starting point, and perhaps a higher baseline would have resulted in an even greater difference. The authors point to a considerable body of research demonstrating the metabolic and cardiovascular benefits of a vegan diet, but this was the first to enroll twins and provide better control for genetic and environmental/cultural confounders.