Effect of Diet and Aging on Human Fecal Microflora

Abstract

The incidence of colon cancer varies widely throughout the world (8, 9). It has been demonstrated that the disease is much rarer in Africa, Asia, and South America than in Western Europe or North America (37) . The reason for this variation is unclear but epidemiological studies, focusing on genetic , cultural, environmental and economic factors suggest that the diet, in particular an increased intake of fat and animal protein, is strongly correlated with the incidence of colon cancer (19, 36) . Epidemiologic studies (7, 31, 36) also suggest that decreases in dietary fiber intake actually increase the incidence of several colonic disorders including: diverticular disease, cancer and constipation. Since some of the predominating bacteria in human fecal contents ferment various types of hemicelluloses (34), it would be of interest to determine the effects, if any, of dietary fiber on the human fecal flora. It is widely known that the composition of fecal flora in healthy infants differed according to the mode of feeding (2, 18, 23) . Although taxonomic studies on Bifidobacterium species present in feces of babies have been carried out (25, 32), the bulk of anaerobes and aerobes from their feces have not been identified at the species level. To address the aforementioned, the present studies were undertaken. Thus, the composition of the fecal flora of the following subjects were compared : (i) breastfed versus bottle-fed infants, (ii) rural Japanese with a low incidence of colon cancer , (iii) urban Canadians with a high incidence of colon cancer, (iv) Japanese volunteers given a high beef or a rice fiber diet (particularly brown rice), and (v) elderly Japanese in rural (Yuzurihara, Uenohara, Yamanashi Prefecture) and urban (Tokyo) areas of Japan, respectively.