More on BMI

Body mass index (BMI) uses your height and weight to estimate your percentage of body fat. BMI numbers at or above 25 are considered unhealthy and are associated with higher blood fats, higher blood pressure, diabetes and an increased risk of heart disease and stroke.

The National Institutes of Health established BMI in 1998 as a means of classifying overweight and obesity. BMI is a better estimate of body fat and health risks than are standard height and weight tables or weight alone. For most people, BMI provides an accurate estimate of weight-related health risks.

However, it's not a perfect guide. Its biggest weakness is that it doesn't consider individual factors such as bone or muscle mass. For example, people who are very muscular and physically fit have relatively high BMIs without added health risks. On the other hand, BMI may underestimate body fat for many older adults or other people with low muscle mass. BMI also may not adequately evaluate health risks of people with excess abdominal fat.

BMI may be an effective tool for determining overweight and obesity in children. However, the numbers require a doctor's interpretation, which takes into consideration the time frames for childhood growth and maturity.