WEIGHT gain bugging you? Evidence is mounting for the central role that bacteria play in causing obesity.

Liping Zhao and his team at Shanghai Jiao Tong University in China put a morbidly obese man on a diet of whole grains, traditional Chinese medicines, probiotics and non-digestible carbohydrates for 23 weeks. The diet was designed to inhibit the bacteria thought to be associated with weight gain by increasing the pH in the colon.

The 175-kilogram volunteer lost 51 kg, despite not exercising. People who have had weight-loss surgery lose on average 49 kg.

To see if the bacteria present also changed, the team looked at what species were prevalent in the volunteer’s gut before and after the diet. Before the regime, Enterobacter – a toxin-producing pathogen – was most abundant, accounting for 35 per cent of the gut bacteria. After the diet, it was reduced to undetectable levels.


The researchers fed mice samples of this bacterium from the volunteer’s gut to determine whether the pathogen was a cause or a result of his obesity. They found that the mice with the new bacteria gained significantly more weight on a high fat diet than control mice, also on a high fat diet (International Society for Microbial Ecology, doi.org/jz9).

Previous work has shown a link between gut bacteria and obesity, but Zhao describes this as “the last missing piece of evidence that bacteria cause obesity“. Treatment with an appropriate diet could be cheaper and more effective than surgery, he says.