The patient also recovered from hyperglycemia and hypertension.

The intestinal bacterium involved was Enterobacter cloacae.

"The endotoxin released by the bacterium can activate a gene that helps generate fat. And it also deactivates a gene that consumes fat," Zhao said at a news briefing on Tuesday in Shanghai.

Zhao's study on the connection between obesity and gut microbiota came from personal experience.

In 2004 when he read the findings about a connection between obesity and gut microbiota in mice, he wondered if such a link existed in humans.

Then he began a diet that combined whole grains and fermented foods, such as yams and bitter melon.

After two years he lost 20 kilograms.

"Intestinal bacteria play an indispensable role in the genesis and development of chronic diseases, such as obesity, diabetes and coronary heart disease. The study will help find how bacteria affect us," Zhao said.

According to the Ministry of Health, China has 120 million people classified as obese.

"Chinese obesity is catching up with Western countries," Qu Shen, an obesity expert from Shanghai No 10 People's Hospital said.

"There are many reasons for obesity, such as lack of physical activity, increased calorie intake, genes, environment and intestinal bacteria," Qu said.

"The new research provides a direction to fight obesity," he said.