One thing to keep in mind, is that Dropsy (aka bloat), a fish disease that can make their belly appear swollen. Do the scales look normal? Usually with bloat, they will point outwards, kind of like a pinecone.
If it doesn't, and its just too much food...
Fish can live for several days without food, so not feeding them for a day or two won't hurt them, but overfeeding DEFINITELY can hurt them! What kind of fish do you have? I have Rosy and Tiger Barbs, and the owner of the local fish store told me 2 flakes per fish per day was enough. He said, "I know the side of the fisk flakes container says feed them several times a day, which they would love you to do, so you have to buy more of their food..."
Considering I buy my food from him, and he just told me to buy it less, I'm guessing he's not lying!
That's what I've been giving my fish, and they seem happy with it, I just try to mix it up occassionally. My Barbs like bloodworms and shrimp, so once a week I'll give them bloodworms, once a week I'll give them shrimp, and the rest of the days I switch between Color-Enhancing flake food, and Advanced Nutrition flake food, and every once in a while, I'll give them a few shelled peas!
I would say, don't feed them today, maybe tomorrow, keep an eye on them, make sure it really is over-eating and not bloat, and then after a couple days, just feed them less than before.