A study published in BMC Medicine compared the effects of a vegan diet versus an omnivorous diet on the biological age of 21 pairs of healthy, adult identical twins. The study comprised two four-week phases: delivered meals and self-provided meals. The participants also received nutritional education about choosing minimally processed foods and building balanced plates. Food intake details were captured at the start of the study and again at week four and week eight. Blood tests were taken at the beginning and end of the study to measure DNA methylation, a marker of biological age. Only the vegan group showed a reduction in biological age, with an average reduction of .63 years after eight weeks on the diet. Reductions in the estimated ages of the heart, hormone, liver, inflammatory and metabolic systems were also noted.