The accumulation of excess abdominal fat is a crucial risk factor for cardio-metabolic disease and recent research has shown that gut microbiota may play an important role in obesity and metabolic disorders. However, little is known regarding the relationship between visceral fat and the human faecal microbiome.
A recent cross-sectional study, led by Prof. Tim Spector and Dr. Jordana Bell from the Department of Twin Research & Genetic Epidemiology at King’s College London (United Kingdom), has found that the human faecal microbiome is related to abdominal adiposity.
The researchers obtained six adiposity measures in total: three measures of abdominal adiposity (visceral fat mass, subcutaneous fat mass, and percentage trunk fat), two measures of body fat distribution (android/gynoid ratio and waist/hip ratio) and a measure of overall obesity (body mass index, or BMI). They used body composition as measured by dual-energy X-ray absorptiometry from 3666 predominantly female twins from the TwinsUK cohort (average age 63 years). Microbiome profiles derived from faecal 16S ribosomal ribonucleic acid (16S rRNA) sequencing were available for 1313 of these individuals.
The researchers identified associations between bacterial diversity in faeces and abdominal adiposity measures. Particularly, the strongest links were found between visceral fat and Oscillospira.
Replication analyses of obesity-microbial associations were pursued in three independent cohorts: the American Gut cohort (n = 2338 individuals), the Flemish Gut Flora Project cohort (n = 917 individuals) and the extended TwinsUK cohort (n = 1031 individuals, not overlapping with samples in the current study). In these independent cohorts, eight BMI-microbial associations from the TwinsUK discovery sample at the current study were replicated.
Heritability analysis of the adiposity-associated faecal bacteria incited the authors to study host genetic-microbiota interactions at obesity-associated human candidate genes. Significant associations of adiposity-associated microbes and host genetic variants in the FHIT, TDRG1 and ELAVL4 genes were found. These data highlight the role of host genes in mediating the relationship between the faecal microbiome and adiposity, which suggests that a proportion of the heritability in obesity could be related to heritable faecal microbes. These results are in line with a previous twin study suggesting that there is genetic control of certain gut microbial taxa and gene-microbe associations involving genes related to diet, metabolism and immunity.
One limitation of the study is its observational nature, which does not explore how bacterial communities might influence the storage of fat in the body or whether a different mechanism takes part. In addition, the studied TwinsUK cohort is mainly female, which does not allow generalisation of results across the general population.
In conclusion, these results suggest that heritable microbes may play a role in determining visceral fat, which is the type of adipose tissue with the most important implications for metabolic health. Besides this, this study adds to a body of evidence suggesting genetic influences on obesity.
Beaumont M, Goodrich JK, Jackson MA, et al. Heritable components of the human fecal microbiome are associated with visceral fat. Genome Biol. 2016; 17(1):189. doi: 10.1186/s13059-016-1052-7.