I can empathize with your situation, when I was younger I too had a problem with gaining weight. However, that's not a problem for me now, but that's another story...

There is a lot of sharp guys here who have backgrounds in proper dieting and nutrition. I do understand your not trying to lose weight, but a proper diet doesn't necessarily mean you have to lose weight...

The best person here that can help you get on the right track would be a Super Moderator by the name of TriGenetics. If you would shoot him a PM (Private Message) and explain your situation, I am sure he would be more then happy to help you acheive your goals...
.
.
.
.