For many of us, the smell of melting butter is almost as delicious as its taste. Ditto for the smoky, sizzly smell of frying bacon. Now, that’s what we call aromatherapy.

But who knew: the smell of human fat, or actually the tendency toward obesity, can be detected by methane levels exhaled in the human breath, according to research underway at Cedars-Sinai in Los Angeles.

The breath of people with an inherited tendency toward obesity also literally tends to be heavier than the breath of skinny people. It’s all due to the presence of archaea, a gut microbiome (in this case, M. Smithii) which is linked to weight gain.