Role of microbes in carbohydrate digestion

Recent developments in the understanding of the role of microbes in digesting carbohydrate in the diet is discussed. Most of the nondigestible carbohydrate from the diet arrives in the large intestine in the form of insoluble plant fiber or particles of resistant starch (RS). Microbial fermentation transforms these indigestible sugars into SCFAs, such as butyrate, propionate and acetate, which supply energy to the host and have multiple effects not only on the gut but also systemically. Understanding microbial degradation of non-digestible carbohydrates is therefore fundamental for designing health-promoting foods and improving health via the diet. When non-digestible carbohydrates are absent from the diet, certain gut bacteria are known to switch to the utilization of endogenous energy sources, especially mucin. Furthermore the ability of certain microorganisms to utilize mucin sugars as a carbon source positions them in close proximity to host cells. The microbial community release soluble carbohydrates that provide energy sources for other bacteria, thus increasing ?energy harvest' from the diet and the formation of fermentation products. The presence of hydrogen-utilizing species causes major shifts in fermentation products and energy yield that can increase substrate breakdown by ruminococci. Understanding the relationship between carbohydrate utilization, microbial ecology and microbiota metabolism is essential to develop novel and sophisticated dietary and nutraceutical strategies to improve human health through the manipulation of the microbiota.