Actually, the registered nurse at my doctor's office told me when I asked her about starting a weightlifting program (S&S) a few years back, to eat MORE so as to stay healthy. She says lots of people try to eat less when lifting weights and they get into some trouble health-wise.
I'm always 100kg. I can't gain and I don't care to lose it. If it's 100kg of strength and power, it's fine.
I tend to be a simple guy: If I am hungry, I eat more, if not I eat less, as long as I stay healthy.
Maybe this video will interest you, from Mike Dolce:
As far as bodyweight goes, most of the old timers were proponent of a strong muscle control, which is trying to use the only muscles required. For instance, Max Sick had an excellent book about that called "Muscle Control" and did pretty impressive feats of strength.