[Dietary fatty acids, intestinal microbiota and cancer]

The interactions between dietary fatty acids (FA) and the intestinal microbiota were reviewed, with their possible relationships to colon and breast cancers. Free and esterified FA in the colon are from dietary, endogenous and microbial origin. Their quantity and quality vary according to dietary FA. Some FA but not all are powerful antimicrobial agents, and different bacteria exhibit distinct sensitivity to FA. These data converge to suggest that dietary FA could influence the biodiversity of the intestinal microbiota and its functions. Conversely, bacteria can modify lipid substrates due to their enormous metabolic potential, and several studies demonstrated that dietary FA did influence the nature of the metabolites produced. Some of these, like hydroxylated FA or sn-1,2-diglycerides, have recognized biological activities on the intestinal mucosa, either as surfactants or intracellular messengers. The intestinal microbiota also represents a substantial source of usual and unusual FA whose biological activities remain to be explored. Dietary FA can influence the secretion of bile and bile acids into the duodenum, the bile acid flux and/or concentration into the feces and that of cholesterol and its bacterial products. This is expected to modify the cytotoxicity of the colonic contents which remains to be evaluated under different lipid diets. Lastly, the intestinal microbiota is very efficient in hydrolyzing conjugated endobiotics and xenobiotics, and this favours the reactivation and the enterohepatic circulation of compounds which have been eliminated through the bile. Hormones are especially concerned, and the intestinal microbiota could thus be implicated in breast cancer. Some dietary FA are known to increase bacterial beta-glucuronidases whereas their effect on other bacterial hydrolases or other enzymes capable of modifying the steroid nucleus remains unknown. In conclusion, numerous data suggest that a strong relationship could exist between dietary FA, the intestinal microbiota and the risk of colon and breast cancer. In the same time, data are still fragmentary so that the effects of dietary FA on the overall biodiversity and numerous functions of the intestinal microbiota cannot be hitherto predicted. Future investigations in this field are discussed.