Bacteria in the human gut could play a vital role in determining who is obese and who is lean, leading to the possibility of creating new treatments to fight obesity, according to a study published in the journal Science.

Led by Dr Jeffrey I Gordon, director of the Centre for Genome Sciences and Systems Biology at Washington University in St Louis, the US study investigated the effect of gut microbiome on obesity from influences such as genes, diet and exercise.

Four sets of identical female twins were recruited for the study, with one twin being lean and the other obese. Using stool samples, researchers collected bacteria, viruses and protozoans present in each participant's gut. These were then placed into a large group of mice.

The study found that the mix of living organisms inside the mice's digestive tracts began to resemble those operating inside their human donors. The mice then went on to develop similar characteristics from the women whose gut microbiomes they had received, with mice that adopted microbiomes from obese women developing obesity and those who received lean transplants remaining lean.

It was then found that the intestinal flora of the lean mice worked better at breaking down and fermenting dietary sugars than the flora of the obese mice. Researchers also found that non-digestible starches passed through the digestive system at a quicker rate in the lean specimens, leading to thinner mice.

With the effects of genes and diet removed from the equation, the experiment helps to understanding the specific ways the gut's organisms influence weight gain.

The research will enable scientists to continue to investigate the specific bacteria involved, with the hope they may be able to introduce such organisms into people who are obese or are predisposed to obesity. Gordon, believes it could be possible to supplement them in people whose gut organisms are not sufficiently equipped to fight obesity.

Some researchers suspect that preservatives and antibiotics in food and medicine – alongside the widespread use of antibacterial cleaners – have changed the bacterial composition of the average person’s gut in ways that could bring about changes in their metabolism, immune system and hormone balance, which could contribute to resulting weight gain.

A breakdown of the study is available here: http://lei.sr?a=Y1q9y