Do your genes make you fat? If so, it might not be your own genes having the effect – it could be the genes of the millions of bacteria living in your gut.
There are quite a few studies now showing associations between the microbiome and various diseases and conditions, including obesity. Some studies have been criticised as showing correlations but claiming cause and effect. Others may be measuring the wrong thing when it comes to obesity - by simplistically looking at body mass index (BMI) rather than more clinically relevant measures such as hip-to-waist ratio or visceral fat. BMI, despite its widespread use, is not a great predictor of mortality; whereas fat within the abdominal cavity is near essential organs and so has a clear effect on cardio-metabolic disease risk.
A new study in Genome Biology is therefore interesting in that it: examines both host genetics and the microbiome; uses multiple measures of human adiposity, including visceral fat, rather than relying on BMI; makes use of 3000 twins from the TwinsUK cohort at King’s College London.
The study has a bunch of confirmatory and novel findings including a high heritability for visceral fat (from host genetics and heritable microbes), an association between specific microbes and obesity and a link between high microbial diversity and low visceral fat.
An on-going challenge of clinical microbiome studies is that they require the researcher to have expert knowledge of (a) microbial genetics / metagenomics and (b) whatever diseases they are looking at. This applies just as well to cancer microbiome studies as it does obesity microbiome studies – and shows the importance of collaboration between these different fields for good experimental design.
The study is available here: http://genomebiology.biomedcentral.com/articles/10.1186/s13059-016-1052-7