A study led by Christopher Gardner from Stanford, published in November 2023 in JAMA Network Open, found that a diet with no animal products lowers cholesterol and insulin levels in identical twins within eight weeks. The trial involved 22 pairs of identical twins, totaling 44 adults around 40 years old, mostly women. Each pair was randomly assigned one twin to a completely plant-based diet and the other to an omnivorous diet. This method reduces the influence of genetic and family history factors on the observed differences. During the first four weeks, participants received all their meals pre-prepared. They then cooked their meals for an additional four weeks. Both groups followed an intentionally healthy diet rich in vegetables and fiber. The main difference was the absence of animal products in the vegan diet, while the omnivorous diet included measured quantities of animal products. In eight weeks, LDL cholesterol, the fraction that clogs arteries, decreased on average from 110.7 to 95.5 mg/dL among the vegan twins. The final difference with their omnivorous twins reached nearly 14 mg/dL, a gain typically achieved after several months of treatment or effort. The same group saw their fasting insulin levels drop by about 20%, indicating better sugar handling by their bodies. The vegans also lost nearly two kilograms more than the omnivores over the same period. This weight loss likely contributed to the benefit, as losing weight lowers cholesterol. However, the difference remains clear even when both groups ate healthily, pointing to an effect specific to plant-based diets beyond just weight loss. The results are notable for their speed, though the study period was short and the number of participants limited. The authors emphasize that eliminating all meat is not necessary to see benefits, as the key seems to be the greater emphasis on plants, especially legumes, whole grains, and nuts. It remains to be seen whether these advantages persist over time. Eight weeks do not indicate what happens to the heart after several years, especially since the two diets tested were already more balanced than the usual diet. Christopher Gardner's team continues its work on longer periods to see if the improvements persist once participants return to their old habits.