It doesn't... literally.
Word by word, it means "good profit", wishing -perhaps- others to get some "health benefit" from the meal they are having. These sentences sound absurd when you translate them into other languages, like "you are welcome" after "thank you": we all laugh the first time we learn it.

wow! i have such a lonnng way to go with the spanish language!!

Lazarus is right, but you can think of this as a succinct way of saying "May this food be of good benefit to you." It doesn't in any way mean "enjoy your meal." That translation is just given as a saying that might be uttered in the same situation, that is, before everyone starts eating. In English, we don't really have any set phrase for this, and it's even slightly stilted to say "enjoy your meal" to the others at the table.

In Japanese, we say itadakimasu before eating anything, which literally means "I receive" in a very formal way, but again there is no good way to translate this into English, because we don't usually say anything in that situation.

Good translations don't translate words, or even concepts, but rather situations.

James Santiago said:

That translation is just given as a saying that might be uttered in the same situation, that is, before everyone starts eating. In English, we don't really have any set phrase for this, and it's even slightly stilted to say "enjoy your meal" to the others at the table.
Sure we do!. In English we say "Bon apetit." Don't we'

samdie said:

Sure we do!. In English we say "Bon apetit." Don't we?

Sam, do behave, please!!...jejejeje

samdie said:

James Santiago said:

That translation is just given as a saying that might be uttered in the same situation, that is, before everyone starts eating. In English, we don't really have any set phrase for this, and it's even slightly stilted to say "enjoy your meal" to the others at the table.

Sure we do!. In English we say "Bon apetit." Don't we?

Chez toi, peut-être.