Human gut microbiota
The human gut microbiota refers to a diverse collection of microorganisms, including bacteria, fungi, archaea, and viruses. Anaerobic organisms that do not require oxygen for growth and survival comprise the greatest microbial biomass in the large intestine
Although some organisms are dominant and widespread in the healthy human gut, a considerable variation in gut microbiota composition and diversity is commonly observed between individuals. The gut microbiota produces a number of primary and secondary metabolites that play a crucial role in maintaining body homeostasis, such as short-chain fatty acids (SCFAs).
Diet is considered a significant driver in modulating gut microbiota composition and activities, which in turn is associated with both positive and negative health effects. An imbalance in the gut microbial community, also known as gut dysbiosis, is known to associate with a range of diseases, including metabolic diseases and colorectal cancer.
Relationship between diet, gut microbiota, and health
Dietary macro- and micronutrients play a significant role in shaping the composition and functions of human gut microbiota. The effect of diet on gut microbiota starts from birth. In breastfed babies, gut microbiota predominantly consists of a bifidobacterial population, which is necessary for the utilization of non-digestible human milk oligosaccharides. In contrast, formula-fed babies exhibit a more complex adult-like gut microbiota composition.
The introduction of solid food in infants leads to the expansion of obligately anaerobic bacterial populations that are able to metabolize more complex polysaccharides. Diet changes the production of metabolites by the gut microbial community. People residing in rural areas generally exhibit higher levels of SCFAs, probably due to higher consumption of dietary fibers.
The gut microbial community obtains energy from dietary compounds that escape digestion by host enzymes, such as resistant starch, non-starch polysaccharides, oligosaccharides, and proteins.
Resistant starch is the primary dietary polysaccharide degraded by the gut microbiota. Bacterial populations containing a complex extracellular starch-degrading structure (amylosome) are able to degrade resistant starch that cannot be digested by host enzymes.
The second major dietary polysaccharides degraded by gut microbiota are non-starch polysaccharides, such as cellulose, pectin, and inulin. Inulin and oligosaccharides are mainly utilized by anaerobic organisms to support growth. These compounds are also used as prebiotics to promote the bifidobacterial community.
