Fermentation of dietary starch in humans

OBJECTIVE: Dietary starch that escapes digestion in the small intestine may be quantitatively more important than dietary fiber as a substrate for fer mentation. The products of fermentation have important implications in the pathogenesis of colorectal cancer and other diseases of the large bowel, wh ich are uncommon in Africans but have a high prevalence in Western populati ons. METHODS: Maize porridge is a staple of most blacks in South Africa. Stale m aize porridge (high-resistant starch [HRS]) seems to induce greater ferment ation in the large bowel than fresh maize porridge (low-resistant starch [L RS]). RESULTS: In the present study, healthy colostomy subjects fed stale maize p orridge had significantly more production of short-chain fatty acids (SCFA) (mean SCFA, HRS = 182.6; mean SCFA, LRS = 116.1; p < 0.05) in their colost omy effluent together with a significant drop in stool pH (mean pH, HRS = 5 .91; mean pH, LRS = 6.70; p < 0.001). The SCFA butyrate (mean, HRS = 35.1; mean, LRS = 17.6; p < 0.05) and acetate (mean, HRS = 93.9; mean, LRS = 65.8 ; p < 0.05) were significantly elevated on the stale maize porridge diet wh en compared with consumption of fresh maize porridge. SCFA propionate (mean , HRS = 43.1; mean, LRS = 24.8; p = 0.05), also increased with stale maize porridge, but was not statistically significant. CONCLUSION: A high-resistant starch diet and its resultant increase in ferm entation products may be partly responsible for protecting the black popula tion against colorectal cancers and other large bowel diseases. (C) 2000 by Am. Cell. of Gastroenterology.