I'm sure mines got an eating disorder. I know when he's hungry because he does the full begging trick when I go near the tank. I'll feed him when he begs, which sometimes can be several times a day, and he'll wolf down the lot. Other times he'll not beg, i'll put some food in anyway and he won't touch it! So I only feed him when he begs now. The longest he's gone without eating, begging, is 4 days, it dosen't seem to bother him. I feed him on his terms now, not when I think he should eat.
And when he does eat he has favourite foods but his fads don't last long before he's onto another favourite food. I can feed him strawberries for example, which he usually loves, then the next day he won't take one piece of strawberry, i'll end up syphoning them out.
Fruits and vegetables are fine but I think they've got to have some "proper" fish food as well which has all the fishy goodness in. My staple is hikari large floating pellets which he's always liked but just recently over the past month or so he's leaving the hikari pellets and just eating his low value fruit and veg.
Whether this nutritional deficit begins to affect him health wise I don't know. Occasionally he goes on a protein romp where he'll only eat prawns, krill, bloodworm and earthworms and then he'll come off it and go back to his fruit and veg. Feeding him is worse than feeding my picky 7 year old lad at times.