Metabolism of Dietary Carbohydrates by Intestinal Bacteria

Abstract

Carbohydrates are significant components of both plant- and animal-based human diets. Depending on the type of diet, calories from carbohydrates can account for more than 70% of total daily energy intake of human adults. Bacteria residing in the colon have greater access to complex carbohydrates, as these molecules are only partially digested in the stomach and not fully absorbed in the small intestine. Microbial metabolism of these dietary microbiota-accessible carbohydrates (MACs) in the colon is important as organic acids such as short-chain fatty acids (SCFAs) produced upon fermentation of MACs are important mediators of host physiology, including promoting intestinal epithelial barrier integrity and development of the immune system. Here we review the microbial metabolism of three different MACs (dietary fiber, polyphenols, and amino sugars) and the enzymes involved in their metabolism. We also discuss advances in tools such as metabolomics and metabolic modeling that are needed for identifying and characterizing products of MAC metabolism by gut bacteria, and suggest future directions of research for elucidating the mechanisms whereby these products influence host physiological processes.