Genes which control gut bacteria could be the key to obesity

Our genes can influence whether we are fat or thin, by determining which bacteria thrive in our gut, scientists have discovered for the first time.

Although obesity genes have been known about for some time, scientists are still trying to understand how genetics influence weight.

In a major development, researchers have now observed how a recently discovered family of microbes in the gut can protect against weight gain and vary in abundance depending on people’s DNA.

The study, carried out by experts at King’s College London and Cornell University in the USA, used groups of identical twins, who share 100 per cent of their genes, and non-identical twins, who share only half their genes, to make accurate comparisons.

Taking 1,000 stool samples from 416 pairs of twins, scientists discovered that populations of gut microbes were more closely similar between identical twins than between non-identical – meaning that the prevalence of at least some of the bacteria in our gut must be influenced by our genes.

The type of bacteria which was most highly influenced by genetic differences was a family of microbes called Christensenellaceae. They were found to be more abundant in low weight people than in obese people.

When administered to mice, Christensenellaceae also appeared to protect them from weight gain.

Professor Tim Spector, head of the department of twin research and genetic epidemiology at King’s, said that the human microbiome was an exciting new target for dietary changes and treatments that could curb obesity.

He said that Christensenellaceae could, in theory, be used as a probiotic in a yoghurt to prevent weight gain, but cautioned studies would be needed to test its effect in humans.

“Seventy per cent of differences between people in how fat they are due to their genes – that’s been known for about 10 years,” he told The Independent. “We know of about 50 genes which are related to obesity but if you add them all together you only account for about one per cent of that difference.

“There’s possibly some big missing factor we haven’t thought of. Finding out if the microbes in our gut are influenced by the host’s genes or not is important. It’s a part of our body we’ve just ignored.”

He said that individual differences in how we respond to food could be explained by variations in gut microbes.

Most of us only share about 40 per cent of our microbes and even identical twins only share 50 to 55 per cent.

In order to better understand how variations influence out responses to diet – for instance, why two people can consume the same amount of calories but experience different rates of weight gain – scientists at King’s are seeking stool samples from members of the public through a project through the British Gut Project. Participants have been invited to sign up for testing pack, and send a sample in the post.

Ruth Ley, associate professor at Cornell University, said: “Up until now, variation in the abundances of gut microbes has been explained by diet, the environment, lifestyle, and health. 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.”