Cummings J H, Bingham S A
Medical Research Council, Dunn Clinical Nutrition Centre, Cambridge.
Cancer Surv. 1987;6(4):601-21.
Diet, especially the amount of starch and dietary fibre which escape digestion in the small intestine, are major determinants of colon function in man. These carbohydrates are the principal substrates for fermentation by the large bowel flora. Carbohydrate fermentation results in lowered caecal pH and the production of short chain fatty acids of which butyric acid may protect the colon epithelium from dysplastic change. Protein digestion and amino acid fermentation also occur in the large bowel but the nature of its endproducts varies in relation to the amount of carbohydrate available. During active carbohydrate breakdown amino acid fermentation endproducts such as ammonia are used by the bacteria for protein synthesis during microbial growth, but in carbon-limited fermentation amines, ammonia, phenols and indoles, etc, accumulate. Fermentation also results in changes in colon pH which alters the metabolism of bile acids, nitrate, sulphate and other substances. Fermentation is thus controlled to a great extent by substrate availability, especially of carbohydrates which are derived from the diet. The potential to induce mutagenic change in colon epithelial cells and promote tumour growth may readily be influenced by diet.
饮食，尤其是在小肠中未被消化的淀粉和膳食纤维的量，是人类结肠功能的主要决定因素。这些碳水化合物是大肠菌群发酵的主要底物。碳水化合物发酵会导致盲肠pH值降低，并产生短链脂肪酸，其中丁酸可能保护结肠上皮细胞免受发育异常变化的影响。蛋白质消化和氨基酸发酵也在大肠中发生，但其终产物的性质会因可用碳水化合物的量而有所不同。在活跃的碳水化合物分解过程中，细菌在微生物生长期间利用氨基酸发酵终产物（如氨）进行蛋白质合成，但在碳限制发酵中，胺、氨、酚和吲哚等会积累。发酵还会导致结肠pH值变化，从而改变胆汁酸、硝酸盐、硫酸盐和其他物质的代谢。因此，发酵在很大程度上受底物可用性的控制，尤其是来自饮食的碳水化合物。饮食很容易影响结肠上皮细胞诱导诱变变化和促进肿瘤生长的可能性。
