The effect of sucrose or starch-based diet on short-chain fatty acids and faecal microflora in rats

An investigation was carried out to determine whether variations of dietary carbohydrates could modify the colonic flora in rats. Sprague-Dawley rats were fed with two equicaloric diets based on the AIN-76 diet (American Inst itute of Nutrition 1977) but differing from that diet in content of carbohy drates, i.e, high sucrose (64%) or high corn starch (64%). Feeding was cont inued for 9 months nd libitum and no variation in weight gain was recorded among the different diets. A prevalence of aerobes, and a significant reduc tion in the ratio anaerobes/aerobes in the faeces of rats on the high starc h diet compared with the high sucrose diet, was observed. The anaerobe gene ra identified included Actinomyces, Bacteroides, Bifidobacterium, Clostridi um, Eubacterium, Lactobacillus and Propionibacterium. Bacteroides was the m ost prevalent genus in both dietary groups (512 and 29.5% in the faeces of rats fed the sucrose and starch diets, respectively). In contrast, clostrid ia were prevalent in the starch-fed group (23.8%) and less so in the sucros e diet (11.5%), as propionibacteria were prevalent in faeces of rats fed th e starch diet (15.5%), and low in the sucrose diet (3.9%). The remaining ge nera were scarce in faeces from rats on either diet. Total short-chain fatt y acids (SCFA) were significantly higher in the faeces of animals fed the s tarch diet compared with those fed the sucrose diet. The relative concentra tions of acetic, propionic and butyric acids were not significantly differe nt between the two dietary groups. In conclusion, high starch diet can mark edly modify the composition of faecal flora and alter considerably the faec al concentration of SCFAs, compounds which might have a health-promoting ef fect.