Composition of Gut Microbiome

This step discusses the various components of the gut microbiome.

Composition of Gut Microbiome

You probably know that billions of micro-organisms live in our bodies, mostly located in the gastrointestinal tract (99% that correspond to up to 2-3 kg). It is estimated that for each human cell there are almost 10 microbial cells and each human gene corresponds to almost 100 microbial genes. The human genome consists of about 23,000 genes, whereas our microbiome encodes over 3 million genes that produce thousands of metabolites. This means that in the human body there is a superorganism that plays an important role. Everyone has a unique microbiota like a personal fingerprint and this means that gut microbiota composition is mostly unique to each individual, like an individual identity card.

Despite some ongoing scientific debate that the womb is not sterile, current evidence points mostly toward that humans live in a sterile environment in the womb and infants only start being colonized by microbes when going through the vaginal passage, or during skin contact with parents or the medical team. The human microbiota is established in this phase and starts out as a dynamic ecosystem that stabilizes during the first 2–3 years. During life the microbial composition increases in both diversity and richness.

Composition is influenced by: feeding methods (breast milk, artificial milk and introduction of solid food); medication (antibiotics, acid suppressants, drug); dietary habits; environment and lifestyle; and weight gain. In addition, there are several factors that cannot be associated with human habits, like genetic factors; anatomical parts of the intestinal tract (e.g. the large intestine has a higher microbial diversity compared with the small intestine); gestational age (preterm or full-term birth); delivery mode (vaginal delivery or C-section); and aging. The microbiomes have many essential functions in the body: from helping digestion and producing vitamins to supporting the development of the immune system and preventing infections.

Impressively there are also interactions between gut microbes and the brain which means we may be able to support mental health by changing the gut microbiome. The microbiome functions as an extra organ, that uses nutrients from ingested foods to produce a large number of compounds, including vitamins, short-chain fatty acids (SCFAs), and essential amino acids. The gut microbiome, through metabolite production and fermentation, helps the intestine to maintain its equilibrium. When a balanced interaction between the gastrointestinal (GI) tract and the resident microbiota is disrupted, intestinal and extraintestinal diseases may develop. The interactions of gut fungal communities with bacteria and viruses are increasingly being explored, and the potential implications for understanding and treating diseases remain an important unanswered question.