Well he can only eat food that has corn starch I think but for now Zim can only eat waffles but later he might get sick.But he might not if they aren't made by Gir.Who knows what he put in them.
ZIM HATES ALL EARTH FOOD THEY CAUSE HIM PAIN!!! for example beans make him ooze green slime and make his head all big, water(i think that counts as a food) feels like acid to irken people, BUT HE LIKES WAFFLES TO SOME EXTENT