Ketones

A friend who once lost some weight said the most interesting part of the experience for her was how bad her breath got. She fancied that maybe toxic compunds dissolved in the fat were being released, but she wasn't sure what it was. I wondered whether it was ammonia: I read somewhere we have roughly 7 parts per billion ammonia in the lungs, which is sufficient to neutralize the acidic aerosols one might encounter in a natural environment.

Apparently the culprits are ketones, which fat turns into upon combustion, particularly with low-carbohydrate diets, and which are volatile and stink (Friends Julia and Fred sent this picture via E-Mail).