Consumption of Japanese Yam Improves Lipid Metabolism in High-Cholesterol Diet-Fed Rats

We investigated the effects of dietary Japanese yam (Dioscorea japonica Thunb.) on lipid metabolism. Male Wistar rats (6 wk old) were fed a high-cholesterol diet for 6 wk and then supplemented with 26% of Japanese yam or 0.5% of its constituent diosgenin for a further 4 wk of high-cholesterol feeding (C6-J4 and C6-D4 groups, respectively). In the C6-J4 group, body weight gains significantly decreased, but skeletal muscle fiber sizes in quadriceps significantly increased compared with the other groups. Furthermore, Japanese yam supplementation resulted in the reduction of triglyceride contents in their liver, quadriceps, and intra-abdominal visceral fat. Diosgenin supplementation resulted in an increase in the numbers of skeletal muscle fibers and decrease in the fat accumulations in liver and of the lipid contents in quadriceps. Although quadriceps cholesterol contents decreased concomitantly with increased serum HDL-cholesterol in both the groups, fecal bile acid, fecal cholesterol contents, and fecal weight were higher in the C6-J4 group than in the C6-D4 group. Meanwhile, we demonstrated that Japanese yam inhibited micellar cholesterol solubility in vitro in a concentration-dependent manner. These results suggest that Japanese yam is more effective than diosgenin in reducing fat accumulation and improving cholesterol metabolism during chronic consumption of a high-cholesterol diet.