What kinds of chemical species that do not belong to the category of fats, carbohydrates or proteins can the body metabolise?
Clarifications: By metabolise, I mean extract energy from (e.g. as ATP). The chemicals would be ingested as “food” regardless of whether they occur in natural dietary nutrients.
I already know of one, ethanol.
At a wild guess, I suspect the body can extract energy from acetate and citrate too.