But researchers are increasingly looking for ways to capture such information with tools as simple and inexpensive as tape measures.
One of the easiest alternatives to the BMI is waist measurement. With growing evidence that fat girdling the waist and visceral organs disturbs metabolism, the circumference of a patient's midsection has been shown to be a better predictor of Type 2 diabetes risk. Several large studies have linked a waist circumference greater than 40 inches for men and 35 inches for women to a higher risk of cardiovascular disease and Type 2 diabetes, as well as earlier mortality -- with every inch beyond those thresholds adding risk.
A twist on that approach, described last month in the journal Obesity, is a measure of hip circumference. When combined with a person's height, the "body adiposity index," proposed by Bergman at USC, offers a simple gauge of how much of a person's body is made up of fat, and what its proportion is to muscle, bone and water.
Finally, an increasing number of researchers cite a major gap in the BMI: its inability to reflect the health effects of a person's exercise habits. At least seven high-profile studies in the last decade have established that even for people with high BMIs, cardiovascular risk and the likelihood of early death are driven down significantly by maintaining a high level of fitness or at least regular physical activity. The risk of Type 2 diabetes also falls, although in that case, studies suggest that whittling waist circumference is a better strategy.