like any food that isn't immediately eaten, it's not a problem unless there is a large amount of it.
tanks are set up to handle a certain amount of decomposing matter, our water changes help manage this by exporting nutrients given off by these processes. so whether it is fish waste, or leftover food, things will break down, and as long as you're not putting in too much, or slacking off on your husbandry in other areas, it shouldn't be an issue.