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Diet and Nutrition

Body Mass Index (BMI) Explained

The Body Mass Index (BMI) is a tool (formula) that helps us compare weight to height in those over 20 years of age and predict the potential for health problems. BMI is easy to calculate, inexpensive and does not require any special equipment. A BMI below 18.5 is considered underweight, 18.5 to 24.9 is considered a healthy weight range, 25 to 29.9 is overweight, and 30 or above is considered obese.

A high or low BMI result may indicate a potential risk for health problems and chronic disease. A low BMI may be indicative of malnutrition, such as anorexia nervosa or cancer. A BMI above 25 is correlated with higher risk for chronic diseases such as diabetes, heart disease and high blood pressure. However, exceptions exist. The BMI does not measure body composition [which will distinguish between muscle and fat]. For example, if we were to compare two men who are 6' tall and weigh 230 pounds, but one was a body builder and the other was a "couch potato," both have a BMI of 31 and fall in the obese range. However, since muscle weighs more than fat, the body builder (being very muscular) is not over fat and most likely does not have a high health risk. The "couch potato" person would be overweight and over fat and would have an increased health risk.

To find out your BMI, try this calculator: Fill in your weight in pounds and height in feet and inches in the boxes below.

Weight:
Height: feet inches

Another BMI Calculator is available from the National Heart, Lung and Blood Institute.

Once the BMI is calculated, you can measure your waist circumference to help evaluate body composition (comparing muscle and fat). The presence of excess fat around the abdomen [the "apple" shaped person] is another predictor of risk for chronic illness. An individual may have a BMI in the healthy range, but still be at risk for health problems because a high waist circumference indicates excessive abdominal fat. A waist circumference greater than 35 inches in women and greater than 40 inches in men indicates excessive abdominal fat (with the exception of pregnancy and a few medical conditions). Pear-shaped individuals may carry excess fat in their hips and thighs, but have less of a risk for chronic illness.

If you find that your BMI or waist circumference puts you at risk for chronic illness, consider speaking with your doctor and a registered dietitian nutritionist. Prevention is the best way to stay healthy.

Source:

Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: Executive Summary. Am J Clin Nutr 1998; 899-917.

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Last Reviewed: Aug 27, 2013

Jane   Korsberg, MS, RD, LD Jane Korsberg, MS, RD, LD
Senior Instructor of Nutrition
School of Medicine
Case Western Reserve University