I'm 21 years old and having hard time gaining weight or fat to me. I eat alot but I'm not gaining any fat in me. I just want to know why? Is it because I have some kind of cancer or what? Is It because I have this kind of worm in the stomach? I've ask alot of question and ppl answers that I'll be fat when I'm older but I don't want that . So any why? and help>?