Obesity in human beings could be caused by bacterial infection rather than eating too much, exercising too little or genetics, according to a groundbreaking study that could have profound implications for public health systems, the pharmaceutical industry and food manufacturers.
The discovery in China followed an eight-year search by scientists across the world to explain the link between gut bacteria and obesity.
Researchers in Shanghai identified a human bacteria linked with obesity, fed it to mice and compared their weight gain with rodents without the bacteria. The latter did not become obese despite being fed a high-fat diet and being prevented from exercising.
The bacterium – known as enterobacter – encourages the body to make and store fat, and prevents it from being used, by deregulating the body’s metabolism-controlling genes.
“This is a very important phenomenon,” said Professor Zhao Liping, who with a team at Shanghai Jiao Tong University carried out the research. “It is the last missing piece of evidence bacteria causes obesity.”
Other academics not linked to the project were quick to seize on its potential implications.
Dr David Weinkove, lecturer in biological sciences at Durham University, said: “If obesity is caused by bacteria, it could be infectious and picked up from some unknown environmental factor, or a parent. It might not be behavioural after all.”
Dr Weinkove said Prof Zhao’s research paved a way to intervene in obesity and could allow new drugs to be developed for treatment.
The study was published in the peer-reviewed journal of the International Society for Microbial Ecology.
Governments around the world are grappling with an obesity pandemic. Chronically overweight people are at a greater risk of suffering from a heart attack, cancer, and diabetes.
According to government and academic studies, nearly 50 per cent of all adults in the US and UK will be obese by 2030.
The UK government estimated that the total cost of obesity – the cost of healthcare as well as the wider burden on the economy – could amount to £50bn a year by 2050 if the pandemic was left unchecked, according to a report by the Department for Business, Innovation and Skills.
Although the Shanghai research was on a small scale, it is bound to add to a heated debate between the health profession and food and drink manufacturers and fast-food chains over responsibility for obesity.
Prof Zhao said treatment with a specially developed diet could be cheaper and more effective than surgery for the morbidly obese and could be available within three years.
There are 10 times more microbes than human cells in our bodies and they can be beneficial. There are between 200 and 300 different species in a typical person.
The Shanghai team fed a morbidly obese man a special diet designed to inhibit the bacterium linked to obesity and found that he lost 29 per cent of his body weight in 23 weeks. The patient was prevented from doing any exercise during the trial.
Prof Zhao said such a loss in an obese patient using this diet was unprecedented. The patient also recovered from diabetes, high blood pressure and fatty liver disease.
The diet of whole grains, traditional Chinese medicines and non-digestible carbohydrates changed the pH in the gut which limited the bacterium’s activity.
Enterobacter also release chemicals, called endotoxins, which cause insulin resistance and a slower uptake of glucose from the blood after eating. Patients take longer to feel full, so they eat more.
A control for calorie intake was not possible as administering the diet with normal bacteria would cause unsustainable hunger, as the bacteria stops fat stores being mobilised and satiating the body, Mr Zhao said.