A taxonomic signature of obesity in the microbiome? Getting to the guts of the matter

Abstract

Obesity is an important and intractable public health problem. In addition to the well-known risk factors of behavior, diet, and genetics, gut microbial communities were recently identified as another possible source of risk and a potential therapeutic target. However, human and animal-model studies have yielded conflicting results about the precise nature of associations between microbiome composition and obesity. In this paper, we use publicly available data from the Human Microbiome Project (HMP) and MetaHIT, both surveys of healthy adults that include obese individuals, plus two smaller studies that specifically examined lean versus obese adults. We find that inter-study variability in the taxonomic composition of stool microbiomes far exceeds differences between lean and obese individuals within studies. Our analyses further reveal a high degree of variability in stool microbiome composition and diversity across individuals. While we confirm the previously published small, but statistically significant, differences in phylum-level taxonomic composition between lean and obese individuals in several cohorts, we find no association between BMI and taxonomic composition of stool microbiomes in the larger HMP and MetaHIT datasets. We explore a range of different statistical techniques and show that this result is robust to the choice of methodology. Differences between studies are likely due to a combination of technical and clinical factors. We conclude that there is no simple taxonomic signature of obesity in the microbiota of the human gut.

Figure 1. There is no association between BMI and the Bacteroidetes:Firmicutes ratio in HMP stool microbiomes.

Figure 2. There is no relationship between BMI and the phylum-level composition of the microbiome.

Each row shows the relative abundance of major gut bacterial phyla in an individual. Individuals are ordered according to their BMI.

Figure 3. The between-study variability in the relative abundance of Bacteroidetes and Firmicutes is greater than the within-study differences between lean and obese individuals.

The Ley data are from . The “Turnb.” data are from Turnbaugh et al. , from African Americans (AA) and European Americans (EA), from variable regions (V) 2 and 6. The MetaHIT data are from the Danish subjects in who do not have inflammatory bowel disease. The HMP data are from V13 and V35. We note that the primary results from this manuscript were generated using data from HMP V35. All p-values by -test.