What is body composition, and why is it important?
Your body is made up of water, fat, protein, carbohydrate and various vitamins and minerals. If you have too much fat -- especially if a lot of it's located at your waist -- you're at higher risk for health problems, including obesity, high blood pressure, high blood cholesterol, diabetes and consequently, heart disease and stroke.

Obesity is recognized as a major, independent risk factor for heart disease. If you are overweight or obese, you would reduce your risk for heart disease when you initiate a weight management program.

Waist circumference and body mass index (BMI) are indirect ways to assess your body composition. Waist-to-hip ratio (WHR) is another index of body fat distribution. However, WHR is less accurate than BMI or waist circumference and is no longer recommended.

What is the waist circumference?
Waist circumference is the distance around your natural waist (just above the navel). If your BMI is equal to or greater than 25 kg/m2, your goal for waist circumference is less than or equal to 40 inches if you are a man and less than or equal to 35 inches if you are a woman.

What is body mass index?
Body mass index assesses your body weight relative to height. It's a useful, indirect measure of body composition because it correlates highly with body fat in most people. Weight in kilograms is divided by height in meters squared (kg/m2). In studies by the National Center for Health Statistics,

• BMI values less than 18.5 are considered underweight.
• BMI values from 18.5 to 24.9 are healthy.
• Overweight is defined as a body mass index of 25.0 29.9. People with BMIs in this range have an increased risk of heart and blood vessel disease.
• Obesity is defined as a BMI of 30.0 or greater (based on 1998 NIH guidelines), or about 30 pounds or more overweight. People with BMIs of 30 or more are at higher risk of cardiovascular disease.
• Extreme obesity is defined as a BMI of 40 or greater.

Some well-trained people with dense muscle mass may have a high BMI score but very little body fat. For them the waist circumference, the skinfold or fatfold measurements, or more direct methods of measuring body fat may be more useful measures.

How do you find your BMI risk level?

1. Use a weight scale on a hard, flat, uncarpeted surface. Wear very little clothing and no shoes.
2. Weigh yourself to the nearest pound.
3. With your eyes facing forward and your heels together, stand very straight against a wall. Your buttocks, shoulders and the back of your head should be touching the wall.
4. Mark your height at the highest point of your head. Then measure your height in feet and inches to the nearest 1/4 inch. Also figure your height in inches only.
5. Find your height in feet and inches in the first column of the Body Mass Index Risk Levels table. The ranges of weight that correspond to minimal risk, moderate risk (overweight) and high risk (obese) are shown in the three columns for each height.

To calculate your exact BMI value, multiply your weight in pounds by 705, divide by your height in inches, then divide again by your height in inches. (Adapted from Obesity Education Initiative: Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, National Institutes of Health, National Heart, Lung, and Blood Institute, Obesity Research 1998; 6 Suppl 2: 51S-209S)