It’s been known for some time that both our genetic make-up and the bugs living in our gut can influence our weight. While previous studies had also hinted that the former may influence the latter, more data was needed to solidify these links. Now, a new study has neatly tied up different strands of the story by confirming that, alongside environmental factors, our genes are indeed an important determinant of our gut inhabitants, which can ultimately influence whether we are thin or fat.
Our bodies are riddled with microbes. So much so that bacteria actually outnumber our own cells by at least ten to one. They even make up around 1 to 3% of our total body mass. They colonize lots of different areas, but perhaps the most diverse site is your gut, where some 500 to 1,000 different species reside.
These bugs, which are collectively known as the gut microbiome, are far from unwanted gate crashers; they provide us with a myriad of benefits, such as assisting the breakdown of food and the production of hormones and vitamins. Changes in our microbiomes can affect our immune system, metabolism, mood and even our behavior by altering our brain chemistry. It’s also become increasingly apparent in recent years that our gut dwellers can influence body weight, and some research has suggested that they could even be affecting our eating decisions. But whether our DNA can shape the bugs that live in our gut and hence affect our metabolic characteristics was hazy.
To find out more, researchers from King’s College London and Cornell University turned to twins. Through genetic sequencing, they scrutinized the microbial composition of 416 pairs of both identical and non-identical twins using more than 1,000 fecal samples.
They found that the abundances of certain types of bugs were more similar in identical twins, who have the same genes, than non-identical twins who are genetically like siblings, sharing around 50% of their genes. This indicated that genes can indeed influence our gut microbiota.
Although they found numerous different groups of microbes whose abundances were influenced by genes, a recently identified family of bacteria called Christensenellaceae turned out to be the most heritable. Further digging revealed that members of this family were more abundant in people with a low body mass index (BMI) when compared with obese people.
To find out how Christensenellaceae could be affecting metabolic characteristics, the researchers transplanted fecal samples from both slim and obese humans into germ-free mice. They found that rodents receiving samples from lean individuals which were enriched with Christensenellaceae gained less weight than untreated mice and those receiving transplants from overweight people. Furthermore, they were also able to reduce weight gain in mice with microbiomes associated with obesity by transplanting just one particular species of Christensenellaceae.
While experts in the field are in agreement that the results support the connection between genetics and our gut microbiome, it has been pointed out that the work is still preliminary and that the impacts of the microbes on body weight remain unclear. However, the authors are still hopeful that the results could eventually be used to aid the search of disease predictors.