being a personal trainer , working at all the healthfood stores, taking almost every supplement. training amatuer bodybuilders...id say low body fat will show muscle defenition, meaning your diet is key. weight training will of course help, but diet is at least 80% of the game, if not more. there are supplements that may help, but without the diet, they are worthless. low weight doesnt mean low bodyfat either. just my two cents.