WASHINGTON -- Maybe it's germs that are making you fat.
Researchers found a strong connection between obesity and the levels of certain types of bacteria in the gut. That could mean that someday there will be novel ways of treating obesity that go beyond the standard advice of diet and exercise.
According to two studies being published in today's issue of the journal Nature, both obese mice and people had more of one type of bacteria and less of another kind.
A "microbial component" appears to contribute to obesity, said study lead author Jeffrey Gordon, director of Washington University's Center for Genome Sciences.
Obese humans and mice had a lower percentage of a family of bacteria called Bacteroidetes and more of a type of bacteria called Firmicutes, Gordon and his colleagues found.
The researchers aren't sure whether more Firmicutes makes you fat or if people who are obese grow more of that type of bacteria.
But growing evidence of this link gives scientists a potential new way of fighting obesity: Change the bacteria in the intestines and stomach. It also may lead to a way of fighting malnutrition in the developing world.
"We are getting more and more evidence to show that obesity isn't what we thought it used to be," said Nikhil Dhurandhar, a professor of infection and obesity at Louisiana State University's Pennington Biomedical Research Center. "It isn't just [that] you're eating too much and you're lazy."
Dhurandhar wasn't part of the research, but said it may change the way obesity is treated eventually.
He said the field of "infectobesity" looks at obesity with multiple causes, including viruses and microbes. In another decade or so, the different causes of obesity could have different treatments. The current regimen of diet and exercise "is like treating all fevers with one aspirin," Dhurandhar said.
In one of the two studies in Nature, Gordon and colleagues looked at what happened in mice with changes in bacteria level. When lean mice with no germs in their guts had larger ratios of Firmicutes transplanted, they got "twice as fat" and took in more calories from the same amount of food than mice with the more normal bacteria ratio, said Washington University microbiology instructor Ruth Ley, a study co-author.
It was as if one group got far more calories from the same bowl of Cheerios than the other, Gordon said.
In a study of a dozen dieting people, the results also were dramatic.
Before dieting, about 3 percent of the gut bacteria in the obese participants was Bacteroidetes. But after dieting, the now normal-sized people had much higher levels of Bacteroidetes -- close to 15 percent, Gordon said.
