Intestinal health functions of colonic microbial metabolites: a review

This review tries to find a scientific answer on the following two questions: (1) to what extent do we understand the specific role of colonic microbial metabolites, especially short-chain fatty acids (SCFA), in maintaining the health status and prevention of diseases of the colon and the host; (2) to what extent can we influence or even control the formation of colonic microbial metabolites which are beneficial for the health status. The review focuses on the following topics: energy source, intestinal motility, defence barrier, oxidative stress with special attention for antiinflammatory and anti-carcinogen functions, and satiety. Also the risk of overproduction of SCFA is discussed. Reviewing the literature as present today, it can be concluded that physiological levels of SCFA are vital for the health and well-being of the host and that the presence of carbohydrates (dietary fibre, prebiotics) is essential to favour the metabolic activity in the direction of carbohydrate fermentation. For optimal motor activity of the ileum and colon, to regulate the physiological intestinal mobility, steadily fermentable dietary fibres or prebiotics are crucial. The formation of SCFA, especially propionate and butyrate, up to high physiological levels in the colon, much likely also contributes to the defence mechanisms of the intestinal wall. No final answer can be given yet about the role of SCFA in anti-inflammation and anti-carcinogenicity, but recently published research shows possible mechanisms in this field. The intake of prebiotics or specific dietary fibres promotes the formation of SCFA within the physiological range, and more or less specifically increases the levels of propionate and butyrate. In this way, they provide benefit to the host, especially the natural regulation of the digestive system.