Johns Hopkins Health Alerts | Nutrition and Weight Control | BMI and Obesity

• While BMI (body mass index) is a general assessment of body weight and disease risk, waist circumference provides a more specific measure of health risk because waist circumference indicates harmful abdominal fat.

Height|weight tables are the most straightforward way to assess your weight, but there are drawbacks to relying solely on this method. The tables are not based on scientific calculations of ideal weight but instead are derived from height, weight, and mortality data of people seeking life insurance. Moreover, they do not take into account body composition.

As the result of the difficulty in directly measuring the amount of body fat and the drawbacks of using height|weight tables alone, researchers have turned to a measurement called BMI to define obesity and its severity. BMI is a measurement of your weight as it relates to your height. BMI correlates strongly with the amount of body fat, though it does not measure it directly.

Federal guidelines define overweight as a BMI from 25 to 29.9 and obesity as a BMI of 30 or greater. Morbid obesity is a BMI of 40 or greater. To calculate your BMI, multiply your weight (in pounds) by 703; divide the result by the square of your height (in inches).

While BMI is a general assessment of body weight and disease risk, waist circumference provides an added and more specific measure of health risk because waist circumference indicates harmful abdominal fat. Research shows that the mortality rates and incidence of certain chronic diseases, such as diabetes and high blood pressure, are substantially higher in those with a disproportionate amount of body fat stored in the abdomen.

Fortunately, abdominal fat is often the first to go with weight loss. Typically, men are prone to fat deposition in the abdomen—developing what is commonly called a pot belly, beer belly, or apple shape—whereas women tend to accumulate fat around the hips, buttocks, and thighs, a distribution called a pear shape. However, women are not immune to accumulating abdominal fat, and weight tends to be stored in a pattern typical to a particular individual (in other words, once a pear, always a pear).

Even in people of normal weight, an increased waist circumference may be linked to an elevated health risk. (A normal waist circumference is less than 40 inches in men and less than 35 inches in women.) And in men and women who are overweight or obese, a large waist circumference increases the already elevated risk of disease. But people with a BMI of 35 or higher have a high risk of disease, regardless of their waist circumference.

Johns Hopkins Health Alerts | Nutrition and Weight Control | BMI and Obesity