Resistant starches of beans reduce the serum cholesterol concentration in rats

We examined the effects of the resistant starches of adzuki (Vigna angularis), kintoki (Phaseolus vulgaris, variety), and tebou (P. vulgaris, variety) beans on the lipid metabolism in rats. Rats were fed a cholesterol-free diet with 25 g of cornstarch (CS)/100 g diet, 25 g of adzuki starch (AS)/100 g diet, 25 g of kintoki starch (KS)/100 g diet, or 25 g of tebou starch (TS)/100 g diet for 4 wk. The cecal contents in the TS group were significantly higher than those in the CS and KS groups. There were no significant differences in body weight or food intake among the groups. The relative liver weight in the CS group was significantly greater than that of the AS, KS, and TS groups. The serum total cholesterol, VLDL+IDL+LDL-cholesterol, and triglyceride concentrations in the AS, KS, and TS groups were significantly lower than those in the CS group throughout the feeding period. Though the total hepatic cholesterol concentration in the TS group was significantly higher than that in the KS group, there were no significant differences between the CS and other starch groups. The cecal pH value in the CS group was significantly higher than that of the bean starch groups. The cecal butyric acid concentrations in the AS, KS, and TS groups were significantly higher than that in the CS group, and the cecal total short-chain fatty acid (SCFA) concentrations in the AS and TS groups were significantly higher than those of the CS group. The fecal cholesterol excretion of the AS, KS, and TS groups were significantly higher than that in the CS group. The fecal coprostanol excretion in the AS group was significantly higher than that in the CS group. There was a negative correlation between the serum VLDL+IDL+LDL-cholesterol concentration and fecal neutral steroid excretion (r = -0.664, p < 0.001) in the present experiment. Furthermore, the cecal total SCFA concentration was negatively correlated with the serum VLDL+IDL+LDL-cholesterol concentration (r = -0.665, p < 0.001) and positively correlated with fecal neutral steroid excretion (r = 0.481, p < 0.05). The cecal butyric acid level was also negatively correlated with the serum VLDL+IDL+LDL-cholesterol concentration (r = -0.609, p < 0.01) and positively correlated with fecal neutral steroid excretion (r = 0.658, p < 0.001). The results suggest that AS, KS, and TS elevate cecal SCFA concentration, in particular butyric acid concentration, and fecal neutral sterol excretion, and lower the serum total cholesterol level.