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Rich or poor in gut bacteria: we are not all equal facing obesity associated diseases

A study published today in Nature could lead to important outcomes in the field of preventive and personalized medicine. Carried out by the European Union-funded MetaHIT consortium ....

29 August 2013. A study published today in Nature could lead to important outcomes in the field of preventive and personalized medicine. Carried out by the European Union-funded MetaHIT consortium led by INRA, this study showed for the first time that 2 groups of individuals can be distinguished in the population, that differ in the composition of their gut bacteria (microbiota). Scientists observed that individuals with low gut bacteria richness are featured by metabolic and inflammatory markers that associate with risk of developing obesity-linked disorders as type 2 diabetes and atherosclerosis. This could lead to the development of a simple identification test for these people at risk and offer them a dedicated preventive solution. The obesity epidemic affected 400 million adults in 2005; it will affect more than 700 million in 2015 and will continue to grow. The causes are partly due to external factors (sedentary lifestyle, easily obtained high energy food …) and partly due to genetic factors. However, the latter seem to account for only a minor part of the trend. More and more data show that variations in our “other” genome, the microbiome, i.e. the global genome of all microorganisms we host in our bodies, may have greater consequences on the onset of obesity than variations in the human genome. Two groups of individuals according to the bacterial composition of the digestive tract The study conducted by the Metagenomics of the Human Intestinal Tract- MetaHIT - consortium focused on a cohort of 292 Danish adults, comprising 123 non-obese and 169 obese. The scientists analyzed their gut bacterial composition with the help of a new analytical approach called quantitative metagenomics. They found that two groups can be distinguished by the richness of bacteria they carry and the abundance of certain bacterial species. A quarter of the cohort is “poor” in bacteria, whereas the rest is “rich”; the difference of richness between the two groups is 68%. This distinction is not dependent on corpulence since lean and obese are found in both groups, even though 80% of the low bacterial richness group are obese. The poor microbiota contains higher proportion of pro-inflammatory and lower proportion of anti-inflammatory bacterial species than the rich one and therefore appears less healthy. The poor and rich individuals can be distinguished with high accuracy by a small number of bacterial species. Gut bacteria richness correlates with metabolic and inflammatory markers in the blood When comparing the two groups, scientists discovered that people with a poor microbiota have more body fat, are more resistant to the action of insulin, have unfavorably altered blood lipids and show increased blood levels of inflammation markers and white blood cells bringing them at increased risk of contracting pre-diabetes, overt type 2 diabetes and cardiovascular disorders. Some bacterial species limit weight gain Researchers also observed that obese people from the poor group gain more weight over time than the lean ones. These individuals either lacked entirely or had a very low abundance of eight particular bacterial species, which might therefore have a protective role against weight gain. Their discovery could lead to the development of new bacteria-therapies which help fight against weight gain. A specific diet enriches the microbiota A complementary study also published in Nature today, focusing on the impact of a high fiber and protein but low calorie diet on the microbiota of obese or overweight French people, independently confirmed the existence of poor and rich microbiota and their metabolic correlates and showed that a weight-lowering diet can improve simultaneously blood-borne risk markers and microbial richness. However, inflammation of individuals with poor microbiota was less efficient. The two studies pave the way for preventive and stratified medicine for chronic diseases, under the assumption that the impending alterations of gut microbial communities towards a less healthy state can be detected early and corrected by appropriate interventions. References Emmanuelle Le Chatelier et al. Richness of human gut microbiome correlates with metabolic markers. Nature, 29 August 2013. DOI: 10.1038/nature12506 accompanying study: Aurélie Cotillard et al. Dietary intervention impact on gut microbial gene richness. Nature, 29 August 2013. DOI: 10.1038/nature12480


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