Doctors led by Ruchi Mathur, director of the Cedars-Sinai Diabetes Outpatient Treatment and Education Center, focused on a methane-producing microbe called Methanobrevibacter smithii. The theory is that M. smithii eats the hydrogen produced by other microorganisms in the gut. Lower hydrogen levels, in turn, increase fermentation in the gut, allowing the body to absorb more nutrients and more energy, or calories, from food.
"Usually, the microorganisms living in the digestive tract benefit us by helping convert food into energy," said 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."
Mathur's previous study on rats, published last year, seemed to indicate that M. smithii promoted weight gain. An abundance of M. smithii could leave detectable levels of methane on the breath of obese human subjects as smoking-gun evidence of this microbe's role in obesity, Mathur said.
Breath test So, Mathur's group analyzed the breath of 792 people. They found that 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.