Weight alone is not a clear indicator of good health because it does not distinguish between pounds that come from body fat and those that come from lean body mass or muscle. Carrying too much fat is a condition called obesity, and puts a person at risk for many serious medical conditions including heart disease, diabetes and even certain forms of cancer. In fact, obesity contributes to at least half the chronic diseases in western society.
Men A, B and C are exactly the same height. A and B have the same weight, and C weighs considerably more. For his height C appears to be fat. But after analyzing body fat levels, B and C have acceptable percentages while A has above the recommended range and is at a higher health risk.