Obesity: the bacteria responsible?

Can the composition of the intestinal flora explain certain weight gains? This is what many researchers think. Explanations.

Trillions of bacteria

Bacteria are teeming in our digestive system: around 100,000 billion bacteria live naturally and autonomously in our intestines, that is to say ten times more than the number of human cells in the body! Overall, our intestinal flora is made up of nearly a thousand species. In total, this represents a mass of approximately 1.5 kg.

With our body, they form an integrated system, which works in symbiosis. The intestinal flora ensures the maturation of the intestinal immune system. Furthermore, the bacteria of the intestine have a high enzymatic potential, they intervene in intestinal transit, the synthesis of vitamins B12 and K, the metabolism of cholesterol, the degradation of nutrients (carbohydrates, lipids, proteins).

Bacteroidetes and firmicutes, two large families of bacteria

Together, firmicutes and bacteroidetes constitute more than 90% of our intestinal flora. Firmicutes include more than 250 genera including lactobacilli, streptococci, enterococci and clostridium. Bacteroidetes, of which there are around twenty different genera, are widely distributed in the environment, including soil, sediments, seawater and animal intestines. These bacteria are abundant in the stools of warm-blooded animals including humans and a group of organisms living in the human oral cavity.

A fragile balance

A healthy digestive system depends on the balance between the billions of bacteria that reside there. Stress, a faulty diet, taking antibiotics or simple fatigue can alter the natural balance in the intestines. And destabilized intestinal flora can lead to indigestion, reduced immunity or a tendency to diarrhea, or even… obesity.

Bacteria that make you obese?

When we compare the bacterial compositions of the intestinal flora of obese people and people of normal build, we see that they differ (1). Two families of bacteria dominate in the intestine: Bacteroidetes and Firmicutes. In obese people, the balance is disrupted in favor of firmicutes. This microbial community has a greater capacity to digest complex carbohydrates. More numerous bacteria extract more calories from food, which leads to an increase in body fat. “ The intestinal flora is more efficient in obese people to extract even more calories, even though they have already gained a lot of energy themselves. “, explains Randy J. Seely, director of the Obesity Research Center at the University of Cincinnati (United States). Balance is restored after weight loss. When obese subjects lost weight over a year, the proportion of firmicutes approached those of lean subjects.

Other studies confirm these results:

• In Spain on adolescents (2);
• In Finland on children and pregnant women;
• In India on children aged 11 to 14 years (3).

Probiotics, bacteria that are really good for your health?

Known for several decades, probiotics are “ live micro-organisms which, ingested in sufficient quantity, produce beneficial effects on the health of those who consume them ”, according to the official definition of the World Health Organization (WHO). There are many probiotics, the best known of which are bifidobacteria and lactobacilli. Names well represented in the “yogurt” section of supermarkets, but probiotics are also found in other fermented foods (sauerkraut, pollen, cold meats, olives, etc.).

The main benefits of probiotics

Probiotics act on several levels:

– They stabilize the intestinal flora by competition with pathogenic bacteria;

– They maintain the barrier function of the intestinal mucosa;

– They modify intestinal ecology;

– They reduce diarrhea associated with antibiotics or rotaviruses;

– They improve the digestion of lactose;

– They would stimulate immunity.

Probiotics that make chickens fat

These same probiotics are, however, used in animal breeding, to make them gain weight faster. Professor Didier Raoult, head of the virology and bacteriology laboratory at the hospital La Timonein Marseille, carried out an experiment on chicks from the same mother (4). The eggs hatched on the same day and the chicks ate the same food. Didier Raoult simply introduced the bacteria into the digestive tract of certain chicks Lactobacillus fermentum. Result : ” Six weeks later, the group of chickens that had ingested the bacteria weighed 30% more than the control chickens », explains Didier Raoult. He obtained similar results with the bacteria bifidobacterium. Results to be confirmed before being able to extrapolate to human physiology.