BMI, or body mass index, is the number calculated using a person's height and weight. According to the Centers for Disease Control and Prevention, or CDC, the BMI is a fairly reliable indicator of body fatness for most people. Although not as accurate as underwater weighing and other methods, it's inexpensive and easy to calculate. Knowing your BMI may caution you about health problems you may encounter based on weight.
How BMI is Calculated
The easiest way to calculate BMI is to plug your height and weight into one of the many online calculators available by searching for "BMI calculator." However, the formula is simple. Divide your weight in pounds by height in inches squared, and multiply by 703. For example, a 5-foot-5 inch female weighs 150 lbs. The height converts to 65 inches. Calculate: [150 divided by (65)² x 703 = 24.96. According to the CDC, this is the high range of normal, with a BMI of 25 or greater considered overweight.
Benefits of a Healthy BMI
The American Heart Association offers several reasons to keep your BMI in a healthy range. BMI indicates whether your weight is healthy, regardless of body frame size. A BMI less than 18.5 is underweight; a BMI between 25 and 29.9 is overweight. A BMI of 30 or greater is obese. People who are a healthy weight have less joint and muscle pain, lower blood pressure and cholesterol, and better blood sugar regulation. This helps lower overall risk for heart disease and some cancers.
BMI Limitations
BMI only examines one risk factor for disease. The National Heart, Lung and Blood Institute recommends evaluating waist circumference as well as other risk factors, such as high blood pressure or a sedentary lifestyle. BMI applies to adults 20 and older. Children and teens have age and sex-specific criteria to consider along with BMI. Very highly trained athletes may have high BMIs due to increased muscle mass, which weighs more than fat, yet not be overweight.
The Role of Body Weight
Body weight is simply a number on the scale. Without context, we don't know whether 140 lbs. is underweight, normal or obese. On a 6-foot man, this is underweight. On a female who is 5 feet 5 inches tall, this is probably a healthy weight. On a 10-year old girl, it's probably obese. Body weight does offer a starting point, however. If your BMI is 27, you can plug various weights into the online BMI calculator to determine what you should weigh. This helps determine the optimal caloric intake to reach a weight-loss goal. To lose 1 lb. a week, you must either burn or consume 3,500 fewer calories each week. It takes 3,500 calories to gain 1 lb. For example, the goal could be to cut 500 calories a day. Eliminate 300 calories daily by reducing snacking, and burn an extra 200 calories by engaging in moderate exercise.
Cautions
Work with your doctor to determine the best weight for you and an appropriate exercise program. Never begin an exercise program without consulting your doctor. Set reasonable goals, and lose weight slowly to best maintain weight loss.
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