There are many ways to provide an estimate of body fat such as body mass index, skinfolds, bioelectrical impedance and underwater weighing. However these methods do not address the distribution of fat. People tend to store fat in specific locations and have been described as either apple or pear shaped to describe those who store fat in the mid-section versus the abdomen or hips.

Accumulation of fat in the abdominal area is associated with insulin resistance, diabetes, lipid disorders and atherosclerosis. A simple measure of waist circumference or the waist-to-hip ratio has great utility in determining risk for heart attack and stroke.

Reference: Kragelund C, Omland T.  A farewell to body-mass index? Lancet. 2005 Nov 5;366(9497):1589-91.