New research from the USA this week has added to the significant number of studies linking obesity and weight control to the composition of bacteria in our gut. Scientists from the Washington University School of Medicine in St Louis believe that obesity may be treated in the future by altering the types of bacteria that live within the gastrointestinal tract.

measuring tape around belly

The new study, led by Jeffrey Gordon, recruited four pairs of twin sisters. In each pair, one woman was obese and the other was of a healthy weight. Stool samples were taken from every woman and the microbes from the stool tests were isolated and transplanted into the gastrointestinal tracts of mice. These mice had been reared in a completely sterile environment and had no gut microbiota of their own.

The scientists found that the mice who had received a faecal transplant from the healthy women stayed slim. Whereas mice put on much more weight when transplanted with the microbes from obese women. The researchers believe that the presence of a particular type of bacteria, called Bacteroides, which were present in much higher concentrations in slim women, played an important role in keeping mice slim.

In a follow up experiment the slim mice and obese mice were made to share the same cage. Mice have a particularly renowned behaviour trait of coprophagia – eating each others’ faeces – and the researchers wanted to see if this impacted the mice’s gut microbiota and, consequently, their weight.

And it did. After 10 days of sharing a cage, obese mice were more lean when fed a healthy diet, high in fibre and low in saturated fats. However, when the diet was switched to low in fibre and high in saturated fats, the obese mice remained overweight.

The scientists theorised that the healthy diet allowed good bacteria to thrive in the mice, which had a significant impact on their weight. The poor diet which mimics a typical “western” diet, low in fibre and high in fat, blocked the effect of the probiotic bacteria.

Jeffrey Gordon commented that the future health implications of this research may lead to a more conscientious development of foods and new therapies to treat obesity.

“In the future, the nutritional value and the effects of food will involve significant consideration of our microbiota, and developing healthy, nutritious foods will be done from the inside out, not just the outside in.”

Here in the UK, Alan Walker and Julian Parkhill from the Sanger Institute in Cambridge called the work, “a step toward the ultimate goal of developing relatively simple mixtures of bacteria for testing as anti-obesity therapeutics.” The Sanger Institute is dedicated to genomic research and is a world leader in the Human Genome Project.

Further reading:

Read about Jeffrey Gordon's previous research into the link between gut microbiota and obesity here. Another recently published study revealed that a certain type of bacteria may aid weight loss, and you may also be interested to read our FAQ "Can probiotics help with weight loss?"

Reference: Gordon, J. et al (2013) Gut Microbiota from Twins Discordant for Obesity Modulate Metabolism in Mice. Science. 6, 341; 6150

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