Nearly 27 percent of United States residents are obese, according to the Centers for Disease Control and Prevention. Add in those who are overweight but not obese, and the total is about two-thirds. Little wonder the U.S. diet industry is, according to the University of New Hampshire, a $60 billion-a-year business. But there is more to finding your ideal weight than counting pounds and ounces. Body mass index, or BMI, gives a fuller picture of whether weight loss should be a priority for you.
Definition
BMI is a screening method to see whether you may have a weight problem. It is a number that you calculate based on your height and weight. It is not a direct measure of the amount of fat on your body, but it produces results that are in line with direct measures, such as underwater weighing and dual-energy x-ray absorptiometry, according to the U.S. Centers for Disease Control and Prevention. BMI's advantages over such methods are its low cost and ready availability.
Process
To calculate BMI in the metric system, divide weight in kilograms by height in meters squared. In the United States standard measurement system, divide weight in pounds by height in inches squared, then multiply the result by 703. The method applies for both adults and children. If you are, for example, 5 feet, 5 inches tall and weigh 150 lbs., your BMI is 24.96.
Interpretation
BMI values for adults age 20 and above fall into standard weight-status categories. Men and women use the same chart. A BMI below 18.5 corresponds to being underweight, 18.5 to 24.9 is normal, 25.0 to 29.9 is overweight and 30 or higher is obese. For youths ages 2 and up, doctors plot BMI on growth charts that account for age and gender.
Limitations
BMI is not a perfect measure. For example, because muscle is heavier than fat, it can overestimate the body fat of highly-trained athletes. It can also underestimate body fat in older adults and others who have lower-than-average amounts of muscle. Additionally, BMI alone does not provide a full picture of your risk for diseases related to being overweight or obese. The National Heart, Lung and Blood Institute recommends considering BMI alongside other predictors, such as waist circumference, blood pressure and level of physical activity.
References
- U.S. Centers for Disease Control and Prevention: About BMI for Adults
- University of New Hampshire: Nutrition
- National Institute of Diabetes and Digestive and Kidney Diseases: Statistics
- National Heart, Blood and Lung Institute: Calculate Your Body Mass Index
- KidsHealth.org: Calculating BMI
- National Heart, Blood and Lung Institute: Assessing Your Weight and Health Risk
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