Gut microbiota, also known as gut flora, is a collection of microorganisms, including bacteria, viruses, archaea, and fungi, that live in the digestive tract of humans. Scientists have calculated that 100 trillion microbes live in the human body, most of them in our guts. These microbes make up the gut microbiota and play crucial roles in human health. There are as many as 1,000 species of bacteria in the human gut microbiota, although each individual has between 250-300 species. 
 
The gut microbiome consists of trillions of microorganisms and their genetic material that live in the gut. Consider your gut microbiome as a vast community of trillions of bacteria and fungi that inhabit every corner of the gastrointestinal tract and impact the metabolism, weight, disease susceptibility, immune system, appetite, and mood. Among the tiny organisms, bacteria that reside in your gut are the most studied. Most of them exert beneficial properties for the health system, including your immune response, but others may cause disruptions of such mechanisms and constitute, consequently, a threat.
Altogether, the organisms that constitute your gut microbiota weigh approximately 1-2 kg. Think about it as an extra organ that plays a vital function in your health, immune system and overall well-being. Scientists agree too on the beneficial activities exerted by your gut microbiota and keep investigating the relationship that the plethora of the organisms may have on human’s key role activities such as metabolism, nutrition, physiology, and therefore health.
 
Needless to say, life without these microorganisms would be different and probably rather difficult. These bacteria are one of the first organisms that you get in contact with. They start colonizing our bodies when we are born and eventually constitute our gut microbiota. We co-develop with them dynamically. Some microorganisms will be more present in our early days while others start populating more later on in life. As we grow, our gut microbiota adapts accordingly. They will be present throughout our lifespan, and affect our health. Hence, getting to know the microorganisms that constitute our gut microbiota may help us have a long-lasting and healthy relationship with them. Researchers agree too, that ensuring an increased diversity of the gut microbiota, may be beneficial to our health and well-being. This guarantees a harmonious equilibrium that permits the bacteria that constitute the gut microbiota to perform many important functions in our bodies.
  

Why Is the Gut Microbiota Important?

The gut microbiota is the subject of in-depth studies in many fields because it has wide-ranging effects on the body, ranging from cognition, behaviour, appetite, metabolism, immunity, and digestive health (the list goes on). Researchers have found that the genomes of bacteria in our gut, the gut microbiome, are 150 times larger than that of humans, meaning our bacteria carry more genes than our human cells. Research shows that gut microbes benefit us by producing vitamins, preventing the growth of harmful bacteria, training the immune system, and fermenting unused food (energy substrates). The gut microbiota also plays vital roles in resistance to an overgrowth in the gut of populations of outsiders that would otherwise cause disease: "good" bacteria compete with "bad" ones. And some even secrete anti-inflammatory compounds.
 
Owing to a significant share in our intestine and whole body, the gut microbiota, is, among others, one of the main regulators of people’s wellbeing. The gut microbiota is involved in several beneficial mechanisms for the host. Some of the most well-known is to ensure the integrity (or barrier) of the gut wall, provide nutrients, vitamins and a source of energy, and protect against pathogens. Furthermore, the gut microbiota is crucial for our immune system. On top of that, the gut microbiota is responsible for breaking down indigestible foods and producing so-called Short Chain Fatty Acids (SCFAs), metabolites that are healthy for you. Among those, acetate, propionate and butyrate are the main metabolites produced and these are involved in processes that regulate the homeostasis of our body. For instance, microbially-produced SCFAs constitute the major energy source of the epithelial cells of the colon (that protect the inside from the outside), provide anti-inflammatory properties, promote gut barrier function and are involved in lipid and glucose mechanisms in the liver.

 

Which Factors Impact the Gut Microbiota?

From the day we are born, we are exposed to different stimuli. The environment we live in, the foods we eat, and the people but also our pets that we interact with, together are important determinants of the overall diversity and composition of the gut microbiota. These factors, and more, can shape our gut microbiota. Factors that have a significant impact on the composition of your gut microbiota are:

• Being born by natural delivery or Cesarean section
• Being breastfed or formula-fed
• Early exposure to antibiotics
• Living in the countryside
• Living with pets
• Diversity in your diet
• Healthy and active lifestyle

Deviating from these factors may generate a less diverse gut microbiota, although the mode of delivery, whether we were breastfed or required antibiotics, are factors that we did not control.
 
But, do not discourage yourself already, because several factors have a major impact on our overall gut microbiota diversity. Starting to act upon your gut microbiota by implementing gut-friendly measures and ensuring our gut health balance, are the actions we may want to embrace.
 
One of the most underestimated factors, yet with major contributions to helping the gut flora thrive, is what constitutes the diet. Scientists discovered that the microorganisms that live in the gut can digest foods that pass through the upper digestive tract intact. These foods are resistant to digestion and constitute the main substrate of the microorganism pool. Through a process referred to as bacterial fermentation, beneficial metabolites are produced and absorbed in the body to exert health functions. These by-products of human bacteria fermentation cannot be produced by the body alone, but need complex mechanisms that are governed by the gut microbiota. The bacteria that we harbour in the gut are particularly efficient at producing these beneficial substances when fueled with the right foods. An example of such foods is vegetables. Vegetables are particularly rich in fibre, a compound that resists digestion and ultimately reaches the large intestine, where the bacteria can use it as a substrate to produce metabolites.
 
Living in the countryside helps shape the gut microbiota too. Being surrounded by a more diverse ecosystem, hence exposed to a different plethora of microorganisms, it is possible to diversify the microbial community. Pets help as well to get exposed to several bacteria that are considered beneficial to further help diversify the gut community.
 
On top of these factors, an active lifestyle is responsible for positively helping the gut ecosystem flourish. Physical activities, among others, release serotonin (a neurotransmitter as known as the ‘happy hormone’) that helps to keep the gut integrity, among other important health-beneficial properties derived from a regular exercise routine. This article is meant to give you an overview and a quick snapshot of some of the myriad functions exerted by your buddies, the tiny organisms that constitute your gut microbiota, and that have co-lived together with you your entire life. 

 

Reference

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4. Bell, V., Ferrão, J., Pimentel, L., Pintado, M., & Fernandes, T. (2018). One health, fermented foods, and gut microbiota. Foods, 7(12), 195.