Obesity may be caused by an imbalance of gases in the body, rather than over-eating or a lack of exercise, researchers claim.

A new study has found that people whose breath has high concentrations of both hydrogen and methane gasses are more likely to have a higher body mass index and higher percentage of body fat.

Now, doctors at the Cedars-Sinai Hospital in Los Angeles say a breath test that identifies microorganisms in the gut may also be able to ascertain how susceptible a person is to developing obesity.

"This is the first large-scale human study to show an association between gas production and body weight - and this could prove to be another important factor in understanding one of the many causes of obesity," said lead author Ruchi Mathur, director of the Diabetes Outpatient Treatment and Education Centre at Cedars-Sinai.


During the study, to be published in the Journal of Clinical Endocrinology & Metabolism, scientists analysed the breath content of 792 people and noticed four patterns.

The subjects either had normal breath content, higher concentrations of methane, higher levels of hydrogen, or higher levels of both gases.

Those who tested positive for high concentrations of both gases had significantly higher body mass indexes and higher percentages of body fat.

The presence of methane is associated with a microorganism called Methanobrevibacter smithii. This organism is responsible for the majority of methane production in humans.

"Usually, the microorganisms living in the digestive tract benefit us by helping convert food into energy," explained Dr Mathur.

"However, when this particular organism - M. smithii - becomes overabundant, it may alter this balance in a way that causes someone to be more likely to gain weight," he said.

These organisms scavenge hydrogen from other microbes and use it to produce methane - which is eventually exhaled.

Researchers suggest this interaction helps hydrogen-producing bacteria thrive and extract nutrients from food more efficiently.

Over time, this may contribute to weight gain.

"Essentially, it could allow a person to harvest more calories from their food," Dr 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."

In an ongoing study funded by the American Diabetes Association, he is working to confirm the link between M. smithii, obesity and pre-diabetic conditions by determining how efficiently people digest food before and after eliminating the microorganism with a targeted dose of antibiotic.

Participants who have evidence of methane on their breath undergo tests such as swallowing a "smart pill" to track how fast the food moves through their bodies.

Incredibly, stool samples are also collected to see how many calories are being harvested during digestion.

Patients are then given antibitoics and the tests are repeated to see if the elimination of the organism results in measureable changes.

"This should let us know just how energy balance is affected by M. smthii," Mathur said.