Rotted milk sounds pretty disgusting but cheese is delicious ... well, some cheeses. A few, I wouldn't argue too strongly against such a definition...
Fermentation is just a matter of doing it with the right things.
And for that matter, don't forget that your gut does a large amount of fermentation -- and you get a fair amount of energy out of the process, not to mention important nutrients. That's a particularly...unappetizing matter, but fortunately it's hidden away inside us for the most part so we don't have to see it except at the end.
(A specific case being, anaerobic fermentation of complex carbohydrates, giving off a combination of methane, hydrogen, CO2 and butyric acid -- a notably smelly short-fatty acid, which is easily metabolized by the body.)
(Incidentally, ethanol is metabolized stepwise to ethanaldehyde then acetic acid, also easily metabolized. So alcoholic drinks, even straight spirits, are as much "empty calories" as pure fat or sugar are.
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Tim