Rarity of colon cancer in Africans is associated with low animal product consumption, not fiber

OBJECTIVE: To investigate whether the rarity of colon cancer in black Afric ans (prevalence, <1:100,000) can be accounted for by dietary factors consid ered to reduce risk, and by differences in colonic bacterial fermentation. METHODS: Samples of the adult black South African population were drawn fro m several rural and urban regions. Food consumption was assessed by home vi sits, food frequency questionnaires, computerized analysis of 72-h dietary recall, and blood sampling. Colonic fermentation was measured by breath H-2 and CH4 response to a traditional meal, and to 10-g of lactulose. Cancer r isk was estimated by measurement of epithelial proliferation indices (Ki-67 and BrdU) in rectal mucosal biopsies. Results were evaluated by comparison to measurements in high-risk white South Africans (prevalence, 17:100,000) . RESULTS: Epithelial proliferation was significantly lower in rural and urba n blacks than whites. The diets of all the black subgroups were characteriz ed by a low animal product and high boiled maize-meal content, whereas whit es consumed more fresh animal products, cheese, and wheat products. Blacks consumed below RDA quantities of fiber (43% of RDA), vitamin A (78%), C (62 %), folic acid (80%) and calcium (67%), whereas whites consumed more animal protein (177% of RDA) and fat (153%). Fasting and food induced breath meth ane production was two to three times higher in blacks. CONCLUSIONS: The low prevalence of colon cancer in black Africans cannot be explained by dietary "protective" factors, such as, fiber, calcium, vitami ns A, C and folic acid, but may be influenced by the absence of "aggressive " factors, such as excess animal protein and fat, and by differences in col onic bacterial fermentation. (C) 1999 by Am. Cell. of Gastroenterology.