Scientists have discovered that bacteria that dwell in the human gut are associated with their host’s obesity or leanness. This work provides clues to how knowledge of the gut microbial community might be used to counter human obesity.
Bacteria that inhabit the gut—the gut microbiota—perform important functions, including breaking down food that could not otherwise be digested. Mouse studies have also suggested that bacterial diversity in the gut may influence whether animal “hosts” are lean or obese, based on differences in the efficiency of specific types of bacteria to extract energy (calories) from food.
In a recent study of obese and lean adult twin sets and their mothers, researchers studied the human microbiota using fecal samples to determine whether host obesity, genetics, or environment is associated with the bacterial composition of the microbiota. To determine which types of bacteria were present in the gut, the researchers analyzed DNA sequences in a particular gene common to all bacteria to identify sequence variations unique to each type. Comparisons revealed that the proportion of different types of bacteria in the guts of obese twins differed from that in the lean twins. Actinobacteria were more abundant than Bacteriodetes bacteria in the obese twins. Conversely, Bacteriodetes were more numerous in the lean twins. Obesity was also associated with significantly less bacterial diversity overall than leanness. Additional analysis revealed that the microbiota of family members are more similar in bacterial composition than unrelated individuals. Surprisingly, the identical twins were not more similar in their gut microbes than fraternal twins, suggesting that composition of the gut microbiota is influenced more strongly by environmental factors than by an individual’s genes. An analysis of bacterial genes represented in the “microbiome”—the combined DNA of the microbiota—found that although the precise composition of the types of bacteria in the gut differs among individuals, people share a “core microbiome” of common microbial genes harbored by the various bacteria. Additionally, comparison of non-core microbiome genes identified over 350 genes that were either enriched or depleted in the microbiomes of obese individuals. Among the genes enriched in the obese gut microbiome, many of which are involved in processing carbohydrates and other metabolic pathways, most were from Actinobacteria and others were from another group of bacteria, Firmicutes.
While this study does not demonstrate cause and effect—whether differences in human microbiota help cause obesity or leanness, or whether obesity or leanness leads to changes in gut microbes—earlier research has shown that the composition of gut microbiota can influence weight gain in mice. This study does demonstrate a significant link between obesity and the gut microbiome, including the identification of several hundred genes that represent biomarkers of unique gut bacterial activity in obese individuals. These biomarkers may lead to more personalized healthcare and potential probiotic interventions to modify the microbial content of the human gut.
Turnbaugh PJ, Hamady M, Yatsunenko T, Cantarel BL, Duncan A, Ley RE, Sogin ML, Jones WJ, Roe BA, Affourtit JP, Egholm M, Henrissat B, Heath AC, Knight R, Gordon JI: A core gut microbiome in obese and lean twins. Nature 4571476-4687, 2009.