Admittedly accurate is the wrong term, but it is a reasonable inductor of health, as the heavier someone is for a given weight, the shorter their expected lifespan will be.

The normal weight may change, but the ideal healthy weight doesn't. The idea of a healthy weight is misleading, as there is more of a healthy body fat percentage. Even that's is an oversimplification, as visceral fat has far more health implications that subcutaneous fat.