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December 8, 2008
Gut Microbiomes Differ Between Obese and Lean People
A new study has found that obese and lean twins have clear differences in their gut microbial communities. The finding points the way for future research into the roles that gut microbes may play in obesity and other health conditions.
The bacteria that live in our gut help us digest our food, prevent infections and may even affect our risk of developing autoimmune diseases like type 1 diabetes. Previous studies have shown that healthy adults have diverse microbial communities in their digestive tracts. Studies in mice have provided hints about how this diversity relates to function. Lean and obese mice have different microbial communities, suggesting that gut microbes influence how efficiently calories from food are harvested and used.
A research team led by Dr. Jeffrey Gordon at the Washington University School of Medicine in St. Louis set out to explore the relationship between obesity and the gut microbiome—the collective genomes of all the microbes living in the gut. With support from 5 different NIH Institutes as well as other sources, the team collected fecal samples from 154 women: 31 pairs of identical twins, 23 pairs of non-identical twins and 46 mothers.
The researchers first sequenced and compared almost 2 million 16S rRNAs from the samples. rRNA is a central component of the protein manufacturing machinery of all living cells, including bacteria. The results, published in the online edition of Nature on November 30, 2008, show that people from the same family have more similar collections of bacteria than unrelated people.
The physical distance between the twins' homes didn’t seem to have an effect on the similarity of their gut communities. There was also no significant difference in the similarity of gut communities between adult identical twins compared to non-identical twins. These results suggest that early environmental exposures play an important role in shaping our gut microbial ecology.
In line with findings from studies of lean and obese mice, the obese twins had a different mix of gut bacteria than the lean twins.
The researchers next sequenced more than 2 billion bases of DNA from a total of 18 people from 6 of the families: 3 lean and 3 obese identical twin pairs and their mothers. Despite the diversity of bacterial species living in their guts, the people shared a broad array of microbial genes—a “core microbiome” representing around 95% of the total DNA sequences. This result shows that although we may not have a core set of bacterial species in our gut, as scientists once thought, the gut’s collective genes and core functions are conserved.
The researchers found differences between obese and lean people in over 300 bacterial genes, many of which are involved in carbohydrate and lipid metabolism. This initial set of markers for the obese gut microbiome is a major step toward understanding the role that gut microbes may play in obesity and its related diseases.
— by Harrison Wein, Ph.D.