Nälkä kasvaa syödessä / The hunger grows by eating
The more you eat, the more you crave, the English equivalent would probably be “I am a bottomless pit”. This applies also to other good things in life besides food.
Apparently the same idea exists in French “L’appétit vient en mangeant.”
On the other hand “ei makeaa mahan täydeltä” / “don’t fill your stomack with sweets” means that you shouldn’t have too much good things.