After a phase of scientific silence on the intestinal flora or microbiota in the study of digestive diseases, exciting revelations make it possible to consider its importance in certain metabolic diseases.
Definition of Microbiote
The microbiota is all microorganisms – bacteria, viruses, parasites, non-pathogenic, commensal fungus called – who live in the small intestine and colon: 2 to 10 times more than the number of cells that make up our bodies, For a weight of 2 kilos. Developing high-throughput sequencing techniques of genetic material have given new impetus to this search. 10 ^ 12 microorganisms, including bacteria, viruses, parasites and fungi are present in the lumen of the digestive tract. There is a common base of 15 to 20 species of the 160 species of bacteria.
The microbiota of an individual is formed as soon as it is born, in contact with the vaginal flora after a low birth, or in contact with environmental microorganisms for those born by Caesarean section.
Under the influence of food diversification, genetics, hygiene level, medical treatment received and the environment, the composition of the intestinal microbiota will evolve qualitatively and quantitatively during the first years of life. Then, the qualitative and quantitative composition of the microbiota remains fairly stable. Medical treatments, changes in lifestyle or various events may also modify the microbiota in a more or less durable way. For example, antibiotic treatment reduces the quality and quantity of the microbiota over several days to several weeks
Role of Microbiote
It plays a role in the digestive, metabolic, immune and neurological functions. It has been recently and abundantly found in hepatic steatosis and steatohepatitis or NASH No alcoholic, which occurs on metabolic syndrome and is associated with diabetes and atherosclerosis. Studies on mice and humans have clearly shown that this microbiote influences the metabolism of the host, acting as a caloric gatekeeper, producing calories from inaccessible nutrient substrates. Thus the microbiota of genetically obese mice has an important ability to harvest and store energy from food. A diet, rich in fats and sugars of rapid absorption, would favor the composition of this flora, then rich in Firmicutes and poor in Bactéroïdetes, with the absorption of extra calories.
Early studies in mice and humans have shown that obesity is associated with lower bacterial diversity: some overweight subjects show a respect for microbial diversity (rich and diverse flora), while others have a microbiota Depleted (about 20 to 40%). The latter most often have a metabolic syndrome with pro-inflammatory bacteria that are just beginning to be identified. The composition of the microbiota also evolves after bariatric surgery (by pass) at least in the short and medium term and in parallel the improvement of the metabolic syndrome.
Ma and collaborators carried out a work involving 4 probiotic studies, including VSL # 3, extensively tested in chronic intestinal diseases, lactobacillus, bifidobacterium and streptococcus, which decrease the intestinal permeability and the passage of toxins in the blood; They would regulate the energy extraction of nutrients and act on the pro-inflammatory cytokines, as well as the genes modulating the metabolism of the substrates. These probiotics reduce transaminases, cholesterol and insulin resistance in patients with NAFLD.
After isolating a family of bacteria called Christensenella minuta, Goodrich and his colleagues transplanted this bacterium into germ-free mice and were able to protect it from weight gain. This paves the way for future bacterial manipulations designed to protect individuals at risk of obesity.
Analysis of the composition of the microbiota also revealed major variations depending on the nature of the feed.
The role of prebiotics (non-digestible ingredients in food) thus begins to develop: they regulate the growth, activity and metabolites of probiotics. The fructo-oligosaccharides thus play an important role in controlling certain colic bacteria. Digestive fermentation products, such as short chain fatty acids or alcohol production in colic light, have also revolutionized the interest of probiotics in steatosis and steatohepatitis
The team of Judith Aron-Wisniewsky (Pitié-Salpêtrière), has tested, in 2016, a dietary change consisting of a calorie reduction, combined with an enrichment of proteins, fibers and carbohydrates. It showed changes in the microbiota composition (approximately 30% increase in bacterial richness) in obese or overweight people. These changes in composition are associated with metabolic and inflammatory improvements.
Pending more precise controlled studies, the addition of natural probiotics, such as yogurts, to the feeding of patients with NASH can only be advised …
In sum, the microbiota has a responsibility in energy storage and certain metabolic disorders. The future is within our reach: modifying the microbiota to offer targeted or individualized treatments.
Ma YY, Li L, Yu et al. Effects of probiotics on nonalcoholic fatty liver disease: ameta-analysis. World J Gastroenterol 2013; 19: 6911-6918
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Alessandro Federico et al. Focus on emerging drugs for the treatment of patients with non-alcoholic fatty liver disease. World J Gastroenterol 2014; 20 (45): 16841-16857
Tilg H, Moschen AR. Food, immunity, and the microbiome. Gastroenterology. 2015; 148: 1107-1119.