Our intestinal intimacy holds one of the keys to the proper functioning of our organism. His secret: a regiment of hundreds of billions of bacteria and yeasts that act unknowingly at short and long distance. Called intestinal flora - or microbiota - it has attracted increasing interest in recent years as scientists begin to measure its considerable importance.

The colon, a major player in our health

This army of invisible roommates is mainly housed in the colon. It helps digest food by fermenting protein, fat and carbohydrate residues, as well as degrading fibers that we are unable to assimilate on their own.

And it provides us with many useful substances, "including vitamins B and K that our body needs daily to be fit," says Dr. Didier Chos, president of the MEI * and co-author of Healthy thanks to micronutrition (Albin Michel ed.)

A piece of intestine guaranteeing immunity

The microbiota, whose composition is specific to each individual, participates in the education of our immune system and provides protection against attacks of pathogens. When the intestinal flora is well balanced, it is indeed made up of 85% of friendly bacteria that secrete natural antibiotics and form a bulwark against parasites. But as soon as it is disturbed, "bad" microbes can take over. In excess, these are likely to alter the permeability of the intestine and allow the passage of large undesirable molecules in the blood.

Deflected, our immune system then over-reacts and turns against its own body. Hence the possible appearance of autoimmune diseases such as rheumatoid arthritis. Digestive hyperpermeability can also be the cause of local inflammatory reactions, which can ultimately induce Crohn's disease or ulcerative colitis.

An influence on the variations of weight

The links between the flora of the colon and our waistline have been proven. In highly coated individuals, the microbiota is notably depleted. Some bacteria, common in slender subjects, are almost absent. Without them, it's hard to lose weight even with proper dieting.

In contrast, "the digestive tract of overweight people is home to more bacteria of the family of firmicutes than that of thin people," says Jeffrey Gordon, the American pope of intestinal microbiology, professor at the Washington faculty of St. Louis. These bacteria, which excel in the extraction of sugar from food, can lead to obesity if the balance of the flora is not quickly restored.

Good news: a few weeks of dietary meals are enough to restore order in our colon and stop the spiral of weight gain.

* European Institute of Dietetics and Micronutrition