A microbe inhabiting the gut could determine whether a person is likely to become obese, a new study shows.

Researchers at Cedars-Sinai Medical Center in Los Angeles, Calif. found gut microbes that could be detected from a breath analyzer. These microorganisms release gases, and if they are measured in high concentrations the person is more likely to have a higher body mass index, BMI, and more body fat.

"This could prove to be another important factor in understanding one of the many causes of obesity", said Ruchi Mathur, lead author and director of the Diabetes Outpatient Treatment and Education Center at Cedars-Sinai.

"Usually, the microorganisms living in the digestive tract benefit us by helping convert food into energy. However, when this particular organism becomes overabundant, it may alter this balance in a way that causes someone to be more likely to gain weight," Mathur said.

The microorganism called Methanobrevibacter smithii, is known to produce methane and consume the hydrogen gas released by neighboring microorganisms in the gut. That increases the fermenting process and boosts the absorption of nutrients from food, which could explain why the person has the affinity to gain more weight.

The study gathered 792 people who had their breath tested for the high concentrations of methane and hydrogen separately and together. However, the presence of both hydrogen and methane could indicate another underlying reason why the subjects are obese. That reason requires further probing.

"This should let us know just how energy balance is affected by M. smthii," Mathur said, "We're only beginning to understand the incredibly complex communities that live inside of us. If we can understand how they affect our metabolism, we may be able to work with these microscopic communities to positively impact our health."

More than 35% of men and women in the United States are considered obese, according to the Centers for Disease Control and Prevention. Researchers say that over-eating habits and lack of exercise are leading contributors to the growing epidemic. Obesity is tied to heart disease and diabetes, among the leading causes of preventable deaths today.

The study is expected to appear in The Endocrine Society's Journal of Clinical Endocrinology & Metabolism in April.