nutrition

Hello, I have joined this group to find out more about nutrition for my son who just had transhiatal EC surgery. He has a coughing  problem making it hard to eat.Anyway, he can not eat much and EN feeding tube causes diarrhea quite often. I am worried how can he regain his stamina? We are vegetarian and sorry to say, but my son is fussy, he loves food with great taste and color. Any help in this area is welcome.