Weisburger J H, Reddy B S, Rose D P, Cohen L A, Kendall M E, Wynder E L
American Health Foundation, Valhalla, New York 10595-1599.
Basic Life Sci. 1993;61:45-63. doi: 10.1007/978-1-4615-2984-2_4.
Fibers in foods are complex carbohydrates. There are several types of fiber, but, for the purpose of mechanistic insight into their mode of protective action in carcinogenesis, classification into two broad types, soluble and insoluble fibers, is warranted. Soluble fibers are present in fruits, vegetables, and certain grains like oats. This type of fiber undergoes metabolism in the small intestine and especially in the large intestine through bacterial enzymes, converting it to products that increase stool size only moderately. But, they have appreciable effects in modifying the metabolism of colon carcinogens like azoxymethane to yield detoxified products and, thus, reducing colon carcinogenesis. In contrast, insoluble fibers present in sizeable amounts in bran cereals, like wheat or rice, are not significantly metabolized by enzymes in the intestinal flora. Such fibers increase stool size substantially through several mechanisms, including higher water retention. The larger bulk dilutes carcinogens, especially tumor promoters such as secondary bile acids, resulting in lower risk of colon cancer in animals and in humans. Evidence in animal models and in humans also indicates that fiber may lower the risk of breast cancer, possibly via an endocrine mechanism. Based on these concepts, increased intake of total fiber, but especially of wheat bran cereal fiber, to yield a daily stool in adults of about 200 grams can significantly reduce the risk of colon cancer and, to a lesser but definite extent, of breast cancer. Thus, adequate fiber intake from cereals, fruits, and vegetables can help prevent important types of human cancer.
食物中的纤维属于复合碳水化合物。纤维有多种类型，但为了从机制上深入了解其在致癌过程中的保护作用方式，将其分为两大类，即可溶性纤维和不溶性纤维是有必要的。可溶性纤维存在于水果、蔬菜以及某些谷物（如燕麦）中。这类纤维在小肠尤其是大肠中通过细菌酶进行代谢，转化为仅适度增加粪便体积的产物。但是，它们在改变结肠致癌物（如偶氮甲烷）的代谢以产生解毒产物方面有显著作用，从而减少结肠癌的发生。相比之下，麸皮谷物（如小麦或大米）中大量存在的不溶性纤维不会被肠道菌群中的酶显著代谢。这类纤维通过多种机制大幅增加粪便体积，包括更高的保水性。更大的体积稀释了致癌物，尤其是肿瘤促进剂，如次级胆汁酸，从而降低了动物和人类患结肠癌的风险。动物模型和人体研究的证据还表明，纤维可能通过内分泌机制降低患乳腺癌的风险。基于这些概念，增加总纤维的摄入量，尤其是麦麸谷物纤维的摄入量，使成年人每天的粪便量达到约200克，可显著降低患结肠癌的风险，并在较小但确定的程度上降低患乳腺癌的风险。因此，从谷物、水果和蔬菜中摄入足够的纤维有助于预防人类重要类型的癌症。
