Effect of resistant starch on colonic fermentation, bile acid metabolism, and mucosal proliferation.

Resistant starch is by definition that part of starch that escapes digestion in the small bowel. Cecal fermentation of resistant starch into short-chain fatty acids will result subsequently in a decrease in pH. Thus, resistant starch may have the same effect on colonic luminal contents and mucosa as some fiber components. We studied the effects of adding 45 g native amylomaize (Hylon-VII) to a standardized diet in 14 healthy volunteers on fermentation and colonic mucosal proliferation. Hylon-VII is a high amylose maize starch, containing 62% resistant starch. During amylomaize consumption, breath hydrogen excretion rose 85% and fecal short chain fatty acid output increased 35% (P < 0.01). Excretion of primary bile acids increased and the soluble deoxycholic acid concentration decreased by 50% (P = 0.002). Subsequently, cytotoxicity of the aqueous phase of feces--as measured on a colon cancer cell line--decreased (P = 0.007). Colonic mucosal proliferation in rectal biopsies (proliferating cell nuclear antigen immunostaining) decreased from 6.7 to 5.4% (P = 0.05). We speculate that resistant starch consumption decreases colonic mucosal proliferation as a result of the decreased formation of cytotoxic secondary bile acids, which is possibly mediated through acidification of the large bowel by production of short-chain fatty acids.