Gut Bacterial Diversity Linked to Obesity's Health Effects

Jenni Laidman

August 31, 2013

The genetic diversity of the bacteria that live in the gut may play a significant role in determining one's tendency toward obesity and its attendant health effects.

A pair of studies published in the August 29 issue of Nature showed that individuals with diverse bacterial populations in their guts were less likely to carry markers associated with increased risk for diabetes and cardiovascular disease than individuals with low genetic diversity in their gut microbiome.

In a study of 292 Danish individuals, 169 of whom were obese, Emmanuelle Le Chatelier, PhD, from the Institut National de la Recherche Agronomique, Jouy-en-Josas, France, and colleagues showed that variation in the microbiome at gene and species levels could define adults at risk for obesity-related disorders.

Individuals with little diversity in gut bacteria had higher levels of overall adiposity, insulin resistance, dyslipidemia, and a more pronounced inflammatory phenotype.

Comparison of the overall number of bacterial gene from all 292 research participants revealed a bimodal distribution. Researchers considered individuals with fewer than 480,000 bacterial genes to have a low bacterial diversity and a low gene count (LGC), and those with more than 480,000 bacterial genes to have a high gene count (HGC). Gut microbiome diversity was low in 23% of participants, which included a higher percentage of obese participants. There was a 40% difference in the average number of genes between the LGC (380,000 genes) and HGC (640,000) groups.

Anti-inflammatory bacterial species were more common in HGC individuals, and potentially pro-inflammatory species were more prevalent in LGC individuals.

Moreover, bacteria in the LGC group had a greater potential for metabolites with negative health consequences, including procarcinogens.

There were significantly more obese individuals in the LGC group than in the HGC group. The difference was significant among men, but not among women. In addition, obese LGC individuals had gained significantly more weight than obese HGC individuals in the last 9 years.

"These findings suggest that stratification of microbial gene richness is predictive of the metabolic and inflammatory status of the host, and may therefore function as a new biomarker," Sungsoon Fang, PhD, and Ronald M. Evans, PhD, both from the Gene Expression Laboratory, Salk Institute for Biological Studies, La Jolla, California, write in an accompanying editorial.

In a separate research letter, Aurélie Cotillard, from the Institut National de la Santé et de la Recherche Médicale, U872, Paris, France, and colleagues show that diet could affect gut microbiome diversity.

In that study, 38 obese and 11 overweight individuals were put on a 6-week high-protein, calorie-restricted diet and then put on a 6-week maintenance program. Eighteen (40%) of the participants were LGC and 27 (60%) were HGC.

The investigators found that after a calorie-restricted diet intervention, they saw a significant increase in genetic diversity in the LGC group, although diversity fell somewhat in the maintenance phase. In addition, genetic richness in the LGC group remained significantly lower than in the HGC group, even after dieting. Gene diversity remained unchanged in the HGC group after the intervention.

Increased gene richness was associated with weight loss and reduced hip circumference, as well as lower circulating cholesterol. However, low-grade inflammation, a contributor to chronic disease, was not affected by the short intervention.

"This suggested that bacterial gene richness is predictive of a person's ability to respond to dietary intervention," the editorialists write.

They also note that neither study yet clarifies whether high genetic complexity simply reflects good health or actually contributes to it. "Further analysis of the aggregate microbial genomes in multiple populations and testing of microbial transplantation may help to resolve these issues," they write.

The authors have disclosed no relevant financial relationships.

Nature. 2013;500:538-539, 541-546, 585-588. Le Chatelier abstract, Cotillard abstract, Editorial extract


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