Fermentation in the Human Large Intestine: Its Physiologic... : Journal of Clinical Gastroenterology (original) (raw)
PRESENTATIONS
Its Physiologic Consequences and the Potential Contribution of Prebiotics
Microbiology and Gut Biology Group, Ninewells Hospital Medical School, University of Dundee, Dundee, UK
The authors declare that they have nothing to disclose.
Key phrases: Diet plays an important role in determining bacterial community structure and regulating metabolic processes in the large intestinal ecosystem; carbohydrate metabolism is the principal driving force maintaining the integrity of the colonic microbiota; prebiotics have been shown to selectively modify the composition and metabolic activities of bacterial communities in the large gut; fermentation and SCFA production are beneficial processes in the large gut, and are responsible for any of the phenomena associated with prebiotic consumption.
Reprints: Sandra Macfarlane, PhD, Microbiology and Gut Biology Group, Ninewells Hospital Medical School, The University of Dundee, Dundee DD1 9SY, United Kingdom (e-mail: [email protected]).
Abstract
The human large intestine harbors a complex microbiota containing many hundreds of different bacterial species. Although structure/function relationships between different components of the microbiota are unclear, this complex multicellular entity plays an important role in maintaining homeostasis in the body. Many of the physiologic properties of the microbiota can be attributed to fermentation and the production of short-chain fatty acids (SCFAs), particularly acetate, propionate, and butyrate. In healthy people, fermentation processes are largely controlled by the amounts and different types of substrate, particularly complex carbohydrates that are accessible to bacteria in the colonic ecosystem. However, other factors impact on bacterial metabolism in the large gut, including large bowel transit time, the availability of inorganic terminal electron acceptors, such as nitrate and sulfate, and gut pH. They all affect the types and levels of SCFA that can be formed by the microbiota. This is important because to a large extent, acetate, propionate, and butyrate have varying physiologic effects in different body tissues. Prebiotics such as galactooligosaccharides together with inulins and their fructooligosaccharide derivatives have been shown to modify the species composition of the colonic microbiota, and in various degrees, to manifest several health-promoting properties related to enhanced mineral absorption, laxation, potential anticancer properties, lipid metabolism, and anti-inflammatory and other immune effects, including atopic disease. Many of these phenomena can be linked to their digestion and SCFA production by bacteria in the large gut.
© 2011 Lippincott Williams & Wilkins, Inc.