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Studies Explore Ties between Low Gut Microbiome Diversity and Obesity, Diet

NEW YORK (GenomeWeb News) – A pair of studies appearing online this week in Nature underscores the gut microbiome differences associated with obesity and related metabolic conditions, while at once revealing dietary contributions to this process.

For the first of the studies, researchers from France, Denmark, China, Germany, and elsewhere — including members of the MetaHIT consortium — used quantitative metagenomic sequencing to tally up the microbial genes found in the guts of 169 obese individuals from Denmark and 123 non-obese controls from the same population. They also relied on array-based 16S ribosomal RNA assessments and phylogenetic analysis to identify the organisms from which these microbial gene sequences originated.

Their data indicated that individuals with higher levels of body fat, insulin resistance, and a propensity for weight gain tended to have fewer microbes in their gut overall, along with a dearth of species diversity in those gut microbial communities.

On the other hand, heavier individuals also had more microbes linked to mild inflammation than their leaner counterparts — an observation supported by the presence of inflammatory markers in blood samples from the overweight individuals in the low microbial diversity group.

Bacteria from Proteobacteria and Bacteroidetes phyla were often over-represented amongst low diversity gut communities, the team noted. And results so far suggest it should be possible to differentiate between species-rich and species-poor gut communities based on the presence or absence of relatively few microbial species.

In the Danish population, for instance, nearly a quarter of those tested had the type of low diversity gut microbiomes that are increasingly being implicated in everything from obesity to an increased risk of heart disease and diabetes.

"Our classifications based on variation in the gut microbiome identify subsets of individuals in the general white adult population who may be at increased risk of progressing to adiposity-associated co-morbidities," co-corresponding author Dusko Ehrlich, with the French National Institute of Agronomic Research (INRA), and his co-authors noted.

In an accompanying study, Ehrlich and other French researchers tracked the gut microbial community changes in dozens of obese or overweight individuals who switched up their diet to include more low-calorie fare.

By doing metagenomic sequencing on microbial DNA in fecal samples from 38 obese and 11 overweight individuals over time, the team was able to see a rise in microbial gene diversity in the gut communities of those who followed a reduced calorie diet for six weeks followed by another six weeks of maintenance dieting.

The presence of certain disease-associated phenotypes — for instance, insulin resistance and elevated blood lipid levels — diminished following the dietary intervention, too, though inflammation tended to linger longer in those with gut communities characterized by lower microbial gene counts.

"Dietary intervention improves low gene richness and clinical phenotypes," the study's authors noted, "but seems to be less efficient for inflammation variables in individuals with lower gene richness. Low gene richness may therefore have predictive potential for the efficacy of treatment."