What role does the microbiota play in digestion?

At every meal, our food is broken down to give us energy and nutrients. At the center of this transformation: our intestinal flora.

It’s lunchtime… But also the beginning of a chain reaction involving many organs. Mouth, esophagus, stomach, small intestine, large intestine… Wherever food goes, it is crushed, decomposed and fragmented by a series of mechanical and chemical phenomena. Objective: to extract the nutrients and energy necessary for the proper functioning of the body.

Its enzymes facilitate the absorption of nutrients

Unusual auxiliary substances play a central role on this long journey, which lasts one to two days: the bacteria that colonize our digestive tract. Without this microbiota, digestion would be much less efficient. First, it has specific enzymes that allow the fermentation of indigestible residues and facilitate the assimilation of nutrients. “The number of microbiota enzymes capable of breaking down complex sugars is estimated at 56,000, while the human genome has only 17 genes encoding this action,” summarizes Philippe Langella, research director at Inrae (the Food and Environmental Research Institute). . And their action doesn’t stop there: bacteria are involved in the synthesis of essential fatty acids and strategic vitamins such as B12, essential for the formation of red blood cells. “They also release substances that have a positive effect on several metabolic pathways, such as regulating blood sugar or inflammation,” says Dr. William Berrebi, gastroenterologist. The breakdown of food by these microorganisms has a counterpart: the gas production that underlies bloating. Don’t pay dearly to reap the benefits of these friendly bacteria.

Two kilos of bacteria wishing us well

Don’t be fooled by their size, of the order of a few microns: the bacteria in our digestive system are so numerous that they weigh between 1.5 and 2 kilos in total. And it’s not the only microbiota that colonizes the human body: populations of microbes nest everywhere (nose, skin, vagina, etc.) with a penchant for moist environments. But their weight does not exceed a few tens or hundreds of grams. This flora is beneficial because, colonizing the soil, it prevents the settlement of possible pathogenic microbes. The gut microbiota is by far the most important, and its function appears to be more complex. When it forms its own organ without which certain foods would not be digested, it also plays a role in immunity and the regulation of our mood.

The stomach: 10 to 1,000 bacteria/ml

It’s an environment not conducive to the microbiota: your mucous membrane produces digestive juices so acidic they would eat away at the stone. This destroys pathogens (bacteria, viruses transmitted with food). Only the good bacteria resist.

The small intestine: 10,000 to 10 million bacteria/ml

Oxygen is scarce here and the environment is less acidic, which offers favorable conditions for the colonization of microorganisms. The bacteria reside between the lumen (ie, the interior of the organ) and the mucus that protects its wall.

The large intestine: 10 billion to 10,000 billion bacteria/ml

It is the great reservoir of the microbiota. The conditions there are optimal for these so-called anaerobic bacteria: constant temperature, low-oxygen environment without oxygen, slow passage… which provides ample food conducive to bacterial development.

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