I'd work with mostly nutritional experiments. Find everyone's maintenance calories.
Mess around with macro's to see if there's any real difference. Also with food quality (some junk, mostly junk, no efa's, all fat's efa's, etc.). Maybe keep them at maintenance, or go hypo or hyper, not too sure.
These would be trained subjects. As much as i learn about nutrition, i still 'want' to believe there are ways to stay lean and put on muscle, albeight slower, i could live with it if i'd stay lean.
I'd also mess with pre/post workout nutrition as opposed to eating whole food meals, see if it really makes much of a difference assuming calories/macros are the same.