Waist circumference (WC), not only body mass index (BMI), indicates obesity-related health risk.
A study using data from the 14,924 adults participating in the National Health and Nutrition Examination Study investigated whether BMI adds to the predictive power of waist circumference in assessing obesity-related comorbidities such as hypertension, cholesterol disorders and metabolic syndrome.
Researchers found that for a given WC value, overweight and obese people and normal-weight people have comparable health risks. However, when WC is evaluated in categories of either normal or high, BMI remains a significant predictor of health risk.
— Diabetes Care, April 2004