An evaluation of the effects of the colonic fermentation of L-rhamnose and lactulose on biosynthesis and serum concentrations of cholesterol and triacylglycerol-fatty acids and serum short-chain fatty acids in humans.

摘要

It has been suggested that the hypocholesterolemic effect of soluble dietary fiber may be mediated by differences in the proportions of acetic and propionic acids produced during its colonic fermentation. To test this, 3 crossover studies were conducted in which the unabsorbable sugars lactulose and L-rhamnose were fed to human subjects. These sugars were chosen because previous studies had shown that in vitro fermentation of lactulose produces mainly acetate while L-rhamnose produces mainly propionate.; Experiment 1. Twenty-two healthy subjects ingested 25 g of lactulose, L-rhamnose, or D-glucose in divided doses over a 12-hour period and serum short-chain fatty acids and breath gases were measured. Compared to D-glucose, L-rhamnose increased serum propionate, while lactulose increased serum acetate, the ratio of acetate to propionate in serum, and breath hydrogen.; Experiment 2. Eleven healthy males ingested 25 g/d of the 3 sugars over three 28-day study periods. Short-chain fatty acid concentrations were measured in serum, urine, and feces. L-rhamnose increased serum propionate, but the increase in serum acetate on lactulose was not significant. However, lactulose increased the ratio of acetate to propionate in both serum and urine.; Experiment 3. Eighteen healthy males ingested 25 g/d of the 3 sugars over three 28-day study periods. Fasting serum lipid concentrations and biosynthesis of triacylglycerol-fatty acids and cholesterol were measured. Fasting serum cholesterol was unchanged but serum triacylglycerol, expressed as a percentage change from baseline, was decreased by both L-rhamnose and lactulose, compared to D-glucose, which raised it. Synthesis of triacylglycerol-fatty acids on day 28 was also significantly lower on L-rhamnose and lactulose than on D-glucose.; In conclusion, the data presented in this dissertation do not support the hypothesis that soluble fiber's hypocholesterolemic effect is mediated by differences in the colonic production of acetate and propionate. However, the ability of both lactulose and L-rhamnose to reverse the hypertriacylglycerolemic effect of an equal weight of D-glucose deserves further study, especially given the importance of elevated triacylglycerol concentrations as an independent risk factor for cardiovascular disease.