Researchers added ‘Body Frame Size’ to refine and define theoretical weights of a person. By determining the frame size, some people will find that they don't need to lose as much weight as they first thought due to the size of their frame. Some may find that they are not in fact big boned and that they need to lose more weight than they had originally thought. The reason for this is that bone structures vary in size and density from person to person and in men and women. The weight of the Bones and the muscle mass can both play a part in determining your optimal weight.