Huang C T, Gopalakrishna G S, Nichols B L
Am J Clin Nutr. 1978 Mar;31(3):516-26. doi: 10.1093/ajcn/31.3.516.
It has been postulated that dietary fiber's protective effect against the development of colon cancer, diverticular disease, and atherosclerosis may be due to the adsorption and/or dilution of intestinal sterols such as bile acids and neural sterols and their bacterial metabolites by component(s) of fiber. Dietary fiber is made up of four major components-cellulose, hemicellulose, lignin, and pectin. There is evidence that hemicellulose and pectin may induce an increase in fecal bile acid excretion in man which may be accompanied by a decrease in serum cholesterol. Natural fibers, such as rolled oats, alfalfa, guar gum, and Bengal gram have been shown to have hypocholesterolemic properties of alfalfa, wheat straw, and some other fibers found considerable amounts of bile acids in vitro. On the other hand, wheat bran, oat hulls, and all the synthetic fibers tested bound only negligible amounts of bile acids under the same conditions. Vegetarians in the United States have lower plasma lipids and different plasma lipoprotein patterns than those of comparable control populations on regular mixed diet. They also have smaller daily fractional turnover rates of cholic acid and deoxycholic acid pool size. In addition, populations on a mixed Western diet, where the rate of large bowel cancer is high (North American, English, Scottish, etc.) degraded and excreted cholesterol and bile acid metabolites to a greater degree than populations where the rate of colon cancer is comparatively low (Ugandan, Japanese, etc). It cannot be denied that the fiber theory linking fiber deficiency with the development of colon cancer and other diseases, is simple, attractive and appears to be firmly based in common sense. When subjected to research studies, however, the situation appears much more complex than expected. Although some progress is being made, the data are often contradictory and confusing, probably due to lack of adequate documentation of fiber intake (e.g., use of dietary fiber instead of crude fiber) and/or the absence of detailed information on the chemistry of the fiber itself.
据推测，膳食纤维对结肠癌、憩室病和动脉粥样硬化发展的保护作用可能归因于纤维成分对肠道固醇（如胆汁酸和神经固醇）及其细菌代谢产物的吸附和/或稀释。膳食纤维由四种主要成分组成——纤维素、半纤维素、木质素和果胶。有证据表明，半纤维素和果胶可能会导致人体粪便胆汁酸排泄增加，这可能伴随着血清胆固醇的降低。天然纤维，如燕麦片、苜蓿、瓜尔豆胶和鹰嘴豆，已被证明具有降胆固醇特性，苜蓿、麦秸和其他一些纤维在体外能发现大量胆汁酸。另一方面，在相同条件下，麦麸、燕麦壳和所有测试的合成纤维仅结合了可忽略不计的胆汁酸量。美国的素食者与食用常规混合饮食且情况相当的对照组人群相比，血浆脂质水平较低，血浆脂蛋白模式也不同。他们胆酸和脱氧胆酸池大小的每日分数周转率也较小。此外，在西方混合饮食人群中，结肠癌发病率较高（北美、英国、苏格兰等），其胆固醇和胆汁酸代谢产物的降解和排泄程度比结肠癌发病率相对较低的人群（乌干达、日本等）更高。不可否认，将纤维缺乏与结肠癌及其他疾病发展联系起来的纤维理论简单、有吸引力，且似乎有坚实的常识基础。然而，在进行研究时，情况似乎比预期复杂得多。尽管取得了一些进展，但数据往往相互矛盾且令人困惑，这可能是由于缺乏纤维摄入量的充分记录（例如，使用膳食纤维而非粗纤维）和/或缺乏关于纤维本身化学性质的详细信息。
