The gut microbiota of Colombian adults with varying body mass index

BACKGROUND: Obesity might be associated with changes in composition and metabolic function of the gut microbiota. Some studies suggest increases in the proportion of Firmicutes and reductions in Bacteroidetes with increasing body mass index (BMI). Others have found discordant patterns. Most studies, however, have focused on North Americans and Europeans, giving a limited picture of the human gut microbiome as the composition of colonic bacteria dramatically varies between individuals/populations. OBJECTIVE: Characterize the gut microbiota of a group of volunteers with varying BMI (adequate weigh, overweight and obese) and quantify concentrations of short-chain fatty acids from a genetically-admixed, independent population. METHODS: Cross-sectional study of 30 Colombian adults of both sexes with varying BMI. The gut microbiota was characterized using pyrosequencing of the 16S ribosomal DNA and concentrations of acetate, propionate and butyrate were quantified by gas chromatography. RESULTS: The gut microbiota of the studied population is mostly composed of Firmicutes and Bacteroidetes with important variations between individuals. Firmicutes and Verrucomicrobia significantly diminish with increasing BMI whereas no change is observed for Bacteroidetes. Acetate significantly increases with BMI, but no change is observed for propionate or butyrate. A more detailed inspection of the data reveals that five fiber-degrading bacteria, including Akkermansia, Dialister, Oscillospira and undetermined Ruminococcaceae and Clostridiales, are responsible of the shifts observed at the phylum level. CONCLUSIONS: The debate concerning the generality of the Firmicutes/Bacteroidetes ratio with respect to obesity is still unresolved. We add a new observation to this debate from an independent population. Our results suggest that the link between gut microbiota and energy balance seems more complex than previously thought. Biological functions of particular bacteria (e.g., fiber degradation) might shed more light into the energy harvest capacity than the analysis of the bacterial composition at the phylum level, and might allow proposing targeted alternatives for preventing and modulating obesity.