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Many studies have reported a link between microbiota and obesity. Unbalanced diet and disrupted microbiota composition could promote weight gain. Could acting on the microbiota put an end to this vicious circle?

Obesity, which affects 15% of the French adult population, is a complex disease in which the gut microbiota plays a key role due do its involvement in the digestive process. Studies on mice have proven it: in the complete absence of microbiota, despite following an identical diet, animals absorb a lesser amount of some nutrients, and thus gain less weight1.

The microbiota varies depending on weight

All microbiotas do not have the same effect on the body mass index. This is why, in mice models, transplantation of human microbiota induces a lesser weight gain if it the donor is thin instead of obese2.

There are differences in the composition of the gut microbiota between people with different builds. The microbiota of obese people seems to be richer in Firmicutes bacteria and poorer in Bacteroidetes3.

However, the causal role of these bacteria in the weight gain process is quite difficult to demonstrate because obese people diet, which is often imbalanced, disrupts the microbiota4.

A causal effect?

Recently, a woman suffering from a Clostridium difficile infection and treated with a fecal microbiota transplant from her overweight daughter, became obese 5. This finding is in line with the hypothesis that, in humans too, the composition of the microbiota has an impact on weight gain.

Diverse mechanisms

This phenomenon could be explained by the effects of the microbiota not only on the absorption of nutrients, but also on the feeling of hunger6 and even on food choices7.

In the future, preventive or therapeutic interventions through gut microbiota modulation could be considered, even if very few trials have been started so far8.



1. BÄCKHED, Fredrik et al. The gut microbiota as an environmental factor that regulates fat storage. Proc Natl Acad Sci USA 2004 ; 101 : 15718-23.
2. RIDAURA Vanessa K et al. Gut microbiota from twins discordant for obesity modulate metabolism in mice. Science 2013 ; 341 : 1241214.
3. LEY et al. Human gut microbes associated with obesity. Nature. 2006;444:1022–1023. doi: 10.1038/4441022a.
4. COTILLARD Aurélie et al. Dietary intervention impact on gut microbial gene richness. Nature 2013 ; 500 : 585-8.
5. ALANG Neha et al. Weight gain after fecal microbiota transplantation. Open Forum Infect Dis 2015 ; 2 : ofv004.
6. BRETON Jonathan et al. Gut commensal E. coli Proteins Activate Host Satiety Pathways following nutrient-induced bacterial growth. Cell Metab 2016. 23 324–334. 10.1016/j.cmet.2015.10.017
7. ALCOCK Joe et al. Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms. BioEssays. 2014;36:940–949. doi: 10.1002/bies.201400071.
8. MUSSO Giovanni et al. Obesity, diabetes, and gut microbiota: the hygiene hypothesis expanded? Diabetes Care. 2010;33:2277–84


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