Everything you always wanted to know about the gut microbiota

The word microbiota generally refers to a range of microorganisms found in a specific environment. The human body has numerous microorganisms living in and on it, such as on the surface or in deeper layers of the skin (skin microbiome), the mouth (oral microbiome), the vagina (vaginal microbiome), and so on.

What is the intestinal microbiome?

The intestinal microbiome (formerly called intestinal flora) is the name given today to the entire microbial population living in our gut.

Our gut microbiome includes tens of trillions of microorganisms, including at least 1000 different species of known bacteria with more than 3 million genes (150 times more than human genes). The intestinal microbiome weighs a total of up to 2 kg. One-third of the species are common across most humans, and two-thirds of species vary from person to person. In other words, the microflora of your gut is an individual identity, a personal imprint.

Where is the intestinal microbiome located?

As its name implies, the intestinal microbiome is located in the intestine, one of the main areas in our body that come into contact with the external environment (other examples constitute the skin and lungs).

Why is the intestinal microbiome important?

Although each one of us has a unique microbiome, it always performs the same normal functions, having a direct impact on our health.

Some of these functions are:

• It helps the body digest certain foods that cannot be digested by the stomach and the small intestine.
• It helps in the production of certain vitamins (B and K).
• It helps fight infections by other pathogenic microorganisms, maintaining the integrity of the intestinal mucosa.
• It plays an important role in regulating the immune system.
• A healthy and balanced intestinal microbiome is the key to the proper functioning of the digestive system.

Considering the very important role that the intestinal microbiome plays in the normal function of the body and the different functions it performs, scientists today consider it as a separate "organ" of the human body. However, it is an "acquired" organ, as newborns are born sterile. More precisely, the colonization of the intestine begins immediately after birth and evolves as we grow older.

When does the formation of the intestinal microbiome begin?

The formation of the intestinal microbiome begins at birth.

The digestive system of the fetus is sterile in the uterus and after birth, it is quickly colonized from microorganisms originated mainly from the mother (vagina, feces, skin, breast, etc.), the environment in which the birth takes place  (hospital, home), the air, etc. From the third day after birth, the composition of the intestinal flora depends directly on how the newborn is fed: for example, the intestinal microbiome of breastfed infants is dominated primarily by Bifidobacteria, compared with infants fed infant milk. In general, we believe that from the age of 3, the intestinal microbiome stabilizes and becomes similar to the microbiome of adults, continuing to evolve at a slower pace throughout life.

How does the intestinal microbiome develop?

The composition of the microbiome evolves throughout our lives, from birth to old age, and is the result of different environmental influences.

The balance of the intestinal microbiome is affected during the aging process and as a result, the elderly have a substantially different microbiome compared to younger adults.

While the general composition of the intestinal microbiome is similar across most healthy humans, the composition of the species is highly individualized and largely determined by our environment and diet. The composition of the intestinal microbiome varies from person to person and is adjusted according to the nutritional intake, either temporarily or permanently. The Japanese, for example, can digest certain seaweeds that are part of their daily diet, thanks to certain special enzymes that their microbiome has acquired from marine bacterial species.

Although the intestinal microbiome can adapt to various changes, in some special cases there may be a loss of balance in the intestinal microbiome. This condition is called dysbiosis. Dysbiosis has been linked to various health problems, such as functional bowel disorders, inflammatory bowel disease, allergies, obesity, diabetes, and more.

Many studies have shown the beneficial effects of prebiotics and probiotics on our intestinal flora. Prebiotics, acting as "food" for certain intestinal microorganisms, contribute to the better functioning of the microbiome. The probiotics found in some fermented foods, such as yogurt, help the gut microbiome maintain its balance, integrity, and diversity.

Thanks to technological advances, the picture of microbes that live in our gastrointestinal system is becoming clearer and clearer. Using a range of molecular biology techniques, we are able to unravel many of the mysteries of the microbiome, and although there are still many undiscovered points, new, striking findings are presented every day.

Basic data and figures of the intestinal microbiome.
 

• The gut microbiome plays an important role in our lives and in the way our body functions.
• The composition of the intestinal microbiome is an individual identity as our fingerprints.
• Our gut microbiome contains tens of trillions of bacteria - ten times more than the cells of our body.
• There are more than 3 million microbial genes in our gut microbiome - 150 times more than genes contained in the human genome.
• The total weight of the microbiome in an adult can reach up to 2 kg.
• There may be more than 1000 different bacterial species in the human intestinal microbiome, but only 150 to 170 of them are common across most humans.