Obesity may not result from what and how much you eat but from bacteria in your guts, researchers now say.
The finding could some day alter the way obese are advised to reduce their weight with combination of diet and exercise. In a discovery of far reaching consequences, researchers found that the make up of microbes in the intestines of obese people are different from those of slim people and they could be helping to gain weight.
They found that microbes taken from fat mouse made and transplanted in another animal's intestine made it gain more than normal fat. The researchers, Nature magazine said, propose that the obese-prone microbes glean more calories from food, which are sucked up by the body and deposited as excess fat.
"Minor differences in the calories you can harvest might play an important role in predisposition to obesity," Jeffrey Gordon at the Washington University School of Medicine in St Louis, who led the studies, was quoted as saying.
The implications for people trying to lose weight are, for now, unclear. It is not known how easy it is to change a person's microbial balance, for example, or whether that might have unwanted health consequences, Nature said.
Stephen Bloom, obesity expert at the Imperial College London, notes that the body's other weight-regulating mechanisms might step in to compensate for any gut microbe changes. Every person's gut is home to a unique cocktail of trillions of bacteria and other minute bugs that help break down food and fight off invading pathogens.
In 2004, Gordon first proposed that this medley of microbes might help control body weight. The studies he and his team publish in Nature this week are the strongest evidence in support of this idea. They strained the faeces of 12 willing obese volunteers, used genetic sequencing to identify the different species of bacteria there, and compared them with five lean volunteers.
Most of the bacteria fell into two groups, called Firmicutes or Bacteroidetes. The obese volunteers had more than 20 per cent more Firmicutes and nearly 90 per cent less Bacteroidetes than the lean ones.
The obese volunteers then spent one year on a low-fat or low-carbohydrate diet, and lost as much as 25 per cent of their body weight, Nature said.
At the same time, the proportion of Firmicutes in their colon dropped and that of the Bacteroidetes rose although these levels never reached those of the group who were slim to start with, it added.
This, Nature says, suggests that our bodies somehow communicate our weight to the microbes in our gut, and that obesity can upset the normal microbial balance. But studies in mice suggest that the reverse is also true: shifting the microbes can affect weight.
The researchers sucked microbes from the guts of either lean mice or the obese ones. They injected the micro-organisms into the intestines of animals whose own innards were unnaturally bare of microbes because they had grown up in a sterile cage.
After two weeks, the mice injected with the 'obese' microbes gained roughly double the quantity of fat than those that received the 'thin' microbes, although this amounted to only a fraction of gram.
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