The culprit, she believes, is a member of archaea known as Methanobrevibacter smithii, which is present in the intestinal tract of about 70% of people, but elevated in about 30%.

CNN: Can you smell obesity?

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.

CNN: Can you smell obesity?

As to importance, when originally identified as distinct, the archaea, too, were regarded as marginal yet their methane-generating properties are now a factor in climate-change calculations.

ECONOMIST: A new domain of life