They do slow down the metabolism, yes.

They seem to also act on some reward mechanism - making some stuff (not just food. Alcohol, gambling, porn, smoking, other drugs have anecdotally been reported to feel less attractive / addictive) have a reduced pull on one's will. They also measurably delay gastric emptying - to the point that some medicines, meant to be taken on an empty stomach, are not safe to take within up to 3 hours from the last meal, compared to one hour or so for other people.