The expanding waistlines of Americans have produced alarming increases in the rates of cardiovascular disease and diabetes. Obesity increases the risk of Metabolic Syndrome, which is the combination of multiple symptoms that include high blood pressure, diabetes, and cardiovascular disease.
Scientists have tried to determine a person’s degree of obesity with measures such as the Body Mass Index (BMI) and the waist-to-hip ratio. The BMI is calculated by dividing the weight in kilograms by the square of the height in meters. The BMI provides a way for identifying people who are too heavy for their height. This is a good screening measure for finding fat people in the general population, but it fails for muscular bodybuilders who have large torsos and small waists. The BMI does not take into consideration whether the excess weight consists of big biceps and pectoral muscles, or a large pot belly and a huge butt.
The waist-to-hip ratio is calculated by dividing the circumference of the waist by the circumference of the hips. This measure determines if the abdomen is too big compared with the hips. Unfortunately, as people gain weight, both their waist and their hips grow. Recently, I posted pictures of Oprah Winfrey and her struggles with diet. Those pictures show that Oprah’s waist and hips increased substantially between 1988 and 2008. Even though Oprah is a lot fatter now, her waist-to-hip ratio is about the same as it was when she was thin. This is the basic defect of the waist-to-hip ratio. A big butt cancels a big waist. This is illustrated in the images above that show the shape of the typical female body for various weights. Clearly, the evaluation of the waist circumference as an anthropomorphic measure should not be done relative to the hips which also increase in size as a person gains weight.
There is a better measure: the waist-to-height ratio. Unlike the hips which increase when a person gains weight, a person’s height remains constant. The waist-to-height ratio is a better measure of the relative size of the abdomen. For a person like Oprah Winfrey, whose height is 66.5 inches, a change of waist size from 28 inches to 36 inches would result in waist-to-height ratios of 0.42 and 0.54, respectively.
 S.D. Hsieh, H. Yoshinaga, T. Muto, Int. J. Obes. Relat. Metab. Disord., 2003 May;27(5):610-6. Waist-to-height ratio, a simple and practical index for assessing central fat distribution and metabolic risk in Japanese men and women.