We are 90% microbes and 10% human.
The human gut is a complex ecosystem and home to millions of microorganisms, including hundreds of species of bacteria. In fact, the human microbiome consists of about 100 trillion microbial cells, outnumbering human cells 10 to 1. There are more than 3 million microbial genes in our gut microbiota –150 times more genes than in the human genome. More than 1,000 different known bacterial species can be found in human gut microbiota, but only around 150 to 170 species predominate in any given subject.
Most of gut microbes are either harmless or beneficial to the host, protecting against enteropathogens (bacterias responsible for food infections), helping extract both nutrients and energy from diets and contributing to the normal immune function. However, some bacteria are potentially dangerous but usually kept in check by beneficial bacteria in what it’s called, the Microbiota Equilibrium.
Disruptions to this delicate balance have been associated to obesity, malnutrition, inflammatory bowel disease, etc. In addition, disturbed microbiota equilibrium can lead to infections of opportunistic pathogens, causing different episodes such as diarrhea. There are different factors that disturb Microbiota equilibrium, such as f.ex. illness and use of medications, i.e. antibiotics.