The human digestive system is simple and complex at the same time. It harbors communities of microorganisms, some of which are beneficial while others are not. Many factors contribute to the establishment of these bacteria in the gut. The food we eat is one major contributor. According to a study, about 60 tons (60,000 kg) of food passes through the gastrointestinal (GI) tract in an average lifespan . An abundance of microorganisms and substrates are carried along with the food and other digested materials. These foreign microorganisms, along with the innate microorganisms found in our gut, make up the gut microbiota.
Biota is coined from the Latin word biote, meaning 'life'. Gut microbiota is the term used for describing the microorganism flora in the gut. To put it simply, it represents all microorganisms present in the gut. They include different types of microorganisms which form symbiotic relationships with the host. Studies have shown that there are 1014 of these organisms present in the GI tract, making it approximately ten times more than the number of human cells in the body . Due to these symbiotic relationships between the microorganisms and the human cells, the human body is considered a superorganism.
The gut microbiota has many functions in the human body, ranging from those related to the gastrointestinal system to metabolism. These roles and functions include aiding in the absorption of nutrients, controlling the population of pathogens, supporting neurological functions and influencing key metabolic processes. Here are 4 key functions of the gut microbiota:
1. Absorption of nutrients
The gut microbiota helps in the fermentation of food molecules such as prebiotic and production of some vitamins like vitamin B and K. It also influences the metabolism of nutrients due to its interactions with the epithelial receptors along the GI lining .
2. Controlling population of pathogens
The competitive-exclusion effect of the gut microbiome is one of the many ways it limits the growth of pathogens in the gut. The gut microbiota competes with these foreign microorganisms for nutrients and at the same time, it secretes antimicrobial compounds such as bacteriocins, which prevent the foreign microorganisms from flourishing and harming the host .
3. Supporting neurological functions
The digestive tract and the brain communicate with each other through a connection known as the gut-brain axis. Messages in the forms of hormonal, immunological, and neural signals travel back and forth between the central nervous system and the gut via this axis. This enables the brain to control certain GI functions such as movement of food through the digestive tract and the release of digestive enzymes. Gut microbiota produces substances that may affect these transmissions .
4. Influencing key metabolic processes
The gut microbiota is also able to influence key metabolic processes such as insulin sensitivity, glucose tolerance, fat storage, and appetite, mainly through the regulation of gut hormones release .