The effect of probiotics on host metabolism: the microbiota and fermentation.

When probiotics are ingested, they become part of the intestinal microflora. Their most important documented effects seem to be 3-fold in supporting or stimulating the immune process and being helpful in treating or affecting the process of infection; affecting luminal pathophysiology that has been shown in many animal experiments; and their role on fermentation of nutrients. Although there is understanding of the role of the microflora on the fermentation process, the effective clinical role is not yet completely understood or shown. The fermentation process consists of the action of bacterial enzymes from the microflora or probiotic organisms on nutrients. The carbohydrate nutrients are the main source of nutrients for the bacterial flora. Although protein and fats may be metabolized by the fermentation process, they are less well understood. Soluble fiber is the main food for probiotic and microbiota organisms. In addition, prebiotic substances are very effective in being metabolized by the organisms. Strains of both Lactobacillus and Bifidobacterium species are effective as lactic acid producing organisms. Their main product is short-chain fatty acids. Butyric, acetic, and propionic are readily produced and either absorbed into the portal circulation or excreted in the stool. Butyrate is the main fuel for colonocytes, whereas acetic and propionic acid are an integral part of cholesterol synthesis. The affect on lipid metabolism by various probiotic organisms and probiotics is discussed. There are some preliminary studies on the importance of the microbiota and the potential importance of probiotic organisms added to this microbiota in lipid metabolism. However, the obvious importance and details of probiotic influence need to be evaluated in future studies.