A while ago on a paleo blog, I remember reading about a former marine's experience (but I can't find it!). He says he gained lots of muscle mass while in the military, where the caloric intake isn't as high as trainers often recommend for putting on mass. He contrasts this with his training experience before joining the military, in which his muscle mass gains were limited, despite eating well and eating lots.
Any thoughts about this? Maybe growth hormone is involved? Sorry if this is a strange question. It's been lurking in my mind for a while now.