Bacteria May Ward Off Obesity

Bacteria in the human gut may play a key role in who is obese or lean and could lead to treatments for obesity, a study finds. The microorganisms in the human gut appear to play a pivotal role in determining whether a person is lean or obese, new research shows. The claim follows a series of experiments which found that the different populations of bacteria that live in lean and overweight people caused mice to lose or gain weight.

Scientists at Washington University School of Medicine in St Louis said the research paved the way for new therapies that tackle obesity by altering the types and numbers of bugs that make their home in the gut.

Researchers  recruited four pairs of women who were twins. One woman in each pair was obese, but the other had a healthy body weight. From each woman, the researchers collected faeces which contained expelled gut microbes. Through a number of tests, the scientists then investigated what happened when they transplanted these into mice bred to have no gut microbes of their own.

The scientists found that mice stayed slim when they received faecal transplants from slim women, but put on much more fat when the samples came from the obese twin. Tests revealed that one type of bacteria, called Bacteroides, was more plentiful in slim women and protected the animals from putting on too much fat.

In a follow-up experiment, mice with microbes from the slim women shared a cage with mice that had microbes from obese women. Because of the animals' would eat each others feces this caused a mixing of the animals' gut microbes.

After the mice had spent 10 days as cage mates, the obese ones had become thinner. But this only happened if the animals were fed a healthy diet that was high in fibre and low in saturated fats. When the diet was switched to high-fat, low-fibre meals the obese mice remained overweight.

The scientists think that a healthier diet allowed "good" microbes to thrive in the animals' guts, and even reverse obesity in the overweight mice. But a more typical western diet, high in fat and low in fibre, blocked the effect. That would explain why there is no "epidemic of leanness" in the US and elsewhere in the west, the scientists say.

The findings, which are published in the journal Science, would steer the development of foods and new therapies that treat obesity by altering the makeup of microbes in the intestines.