Can you smell obesity?

It turns out that obesity may be detectable as a gas, thanks to organisms that inhabit our gut. In a study published in the Journal of Clinical Endocrinology & Metabolism, researchers extend our knowledge about the hidden universe of the microbes that live within us to show that obesity is associated with certain populations of microbes that give off a distinctive gas.

To be more specific, obesity may smell a lot like ... methane, which is to say, like not much at all, since methane in its naturally-occurring state is actually odorless.

In the study, Dr. Ruchi Mathur, director of diabetes in the department of medicine at Cedars-Sinai Medical Center, and her colleagues analyzed the breath of 792 men and women of various ages.

Mathur focused on detecting methane in the breath, since animal studies found that the presence of a certain family of organisms called archaea, which are older than bacteria and colonize the gut, was linked with weight gain and conveniently released small amounts of methane gas.

Mathur also knew from her own work analyzing the gas makeup of the breath from bariatric surgery patients that those releasing higher levels of methane in their breath tended to have a body mass index (BMI) nearly seven points higher on average than those with lower levels.

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And sure enough, Mathur found that among the nearly 800 participants she tested, those with higher levels of methane (three or more parts per million over 90 minutes) and hydrogen gases (20 or more parts per million) in their breath also tended to be heavier, with a BMI about 2.4 points greater than those with normal levels of the gases and about 6% more body fat on average.

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