Effects of Taiwanese yam (Dioscorea japonica Thunb var

Objective: This study investigated the effects of a Taiwanese yam, Dioscorea japonica Thunb var. pseudojaponica Yamamoto, on upper gut function and lipid metabolism in adult Balb/c mice.

Methods: Mice were randomly allocated to consume the control, 25%, or 50% yam diet in which yam in an uncooked lyophilized form was incorporated into the diet for 21 d.

Results: Growth rates were similar among groups, even though the apparent protein absorption rate was decreased by the 50% yam diet. Both yam diets decreased gastric villous width but did not significantly modulate other morphologic and proliferative indices. Brush-border leucine aminopeptidase activities in the small intestine were increased approximately 30% by the 25% and 50% yam diets, respectively. In contrast, sucrase activity was decreased 40% by the 25% yam diet and 50% by the 50% yam diet. The 50% yam diet consistently improved the cholesterol profile in the plasma and liver, whereas the 25% yam diet reduced only the level of low-density lipoprotein cholesterol in plasma. Changes in blood lipid levels were associated with reduced fat absorption.

Conclusion: A 25% uncooked yam diet may benefit upper gut function and prevent hypercholesterolemia in humans, but the 50% yam diet negatively affected protein absorption.