Obesity 'bug' on breath may offer clues on weight gain

A microorganism living in the human digestive tract may give clues into why some of us gain weight, no matter the diet and exercise.

A study from Cedars-Sinai found a breath test might help doctors determine if a person has that troublesome bug living in the gut, and thus is more susceptible to obesity.

The microorganism, called Methanobrevibacter smithii, makes its presence known through the concentration of high methane levels in the breath. People with higher levels of methane are more likely to have higher body mass indexes and higher percentages of body fat.

"Usually, the microorganisms living in the digestive tract benefit us by helping convert food into energy," said Ruchi Mathur, the lead author of the study and the director of the Diabetes Outpatient Treatment and Education Center at Cedars-Sinai. "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."

The study, which will be published in April's issue of the Journal of Clinical Endocrinology & Metabolism, posits that M. smithii, which scavenges hydrogen from other digestive tract microbes and turns it into methane, makes other bacteria more efficient.

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

The study, in which 792 people consumed a standard diet over three days and track how quickly food moves through the body and how much caloric value is extracted from the food before and after antibiotics are used to remove some of the M. smithii from the digestive tract.