Genetics may be a reason why blood levels of low-density lipoprotein ("bad") cholesterol vary greatly between individuals. To investigate the gene link, researchers studied the responses of 28 pairs of identical male twins with diets either high or low in fat; one brother was a devoted exerciser while the other one was a "couch potato."
During the first 6 weeks, the participants ate either a low-fat diet (20% of the calories from fat) or a high-fat diet (40% of the calories from fat). The twins switched diets for the latter 6 weeks of the study. After each 6-week period, the twins' blood cholesterol levels were checked. The results of the study indicated a strong similarity in the way each twin responded to the diets, regardless of whether he exercised or not.