A joint study from King’s College London and the USA’s Cornell University published in the journal Cell, reveals our genetic makeup influences whether we are fat or thin by shaping which types of microbes thrive in our body.

By studying pairs of identical and fraternal twins at King’s Department of Twin Research, the researchers identified a specific, little-known bacterial family that is highly heritable and more common in people with low BMI. When this microbe was transplanted into mice, it protected against weight gain.

Previous studies have linked both genetic variation and the composition of gut microbes to metabolic disease and obesity, but notwithstanding these shared effects, it was presumed the relationship between human genetic variation and the diversity of gut microbes was negligible.

Researchers involved in this new study sequenced the genes of microbes taken from more than 1000 faecal samples from 416 pairs of twins. The abundances of specific types of microbes were found to be more similar in identical twins, who share 100 per cent of their genes, than in fraternal twins, who share on average only half of the genes that vary between people.

These findings demonstrate that genes influence the composition of gut microbes.

The type of bacteria whose abundance was most heavily influenced by host genetics was a family called Christensenellaceae, first described just two years ago. Members of this health-promoting bacterial family were more abundant in participants with low body weight than in those who were obese. Mice treated with this microbe gained less weight than untreated mice, suggesting that increasing the amounts of this microbe could help to prevent or reduce obesity.

“Until now, variation in the abundances of gut microbes has been explained by diet, the environment, lifestyle, and health,” says Ruth Ley, Associate Professor at Cornell University in the United States. “This is the first study to firmly establish that certain types of gut microbes are heritable: that their variation across a population is in part due to host genotype variation, not just environmental influences. These results will also help us find new predictors of disease and aid prevention.”

Professor Tim Spector, Head of the Department of Twin Research and Genetic Epidemiology at King’s College London, comments that the human microbiome represents an exciting new target for dietary changes and treatments aimed at combating obesity. “Twins have been incredibly valuable in uncovering these latest links, but we now want to promote the use of microbiome testing more widely in the UK through the British Gut Project. We want thousands to join up so we can continue to make major discoveries about the links between our gut and our health.”

Launched in October 2014 British Gut – the UK’s largest open-source science project to understand the microbial diversity of the human gut – is a collaboration between the Department of Twin Research at King’s College London and American Gut.

Although further research is needed, it’s hoped these findings may open the way for personalised probiotic therapies optimised to reduce the risk of obesity-related diseases based on a person’s genetic make-up.

Written for the Australian Traditional-Medicine Society (ATMS) by Rosemary Ann Ogilvie from materials released by Kings College London.