Body mass index, or BMI, is a measurement that uses height and weight to obtain information about your amount of body fat. Doctors use BMI as a way to pick out individuals at a high risk of developing weight-related health conditions. A high BMI indicates a potentially higher risk of heart disease, breathing problems, high blood pressure and diabetes. In contrast, a low BMI could be a sign of poor nutrition, malabsorption disorders or other health conditions.
Measurement
To calculate your body mass index in the English system of measurement, divide your weight in pounds by your height in inches squared, and multiply by 703. This number is your BMI measurement. If you are using the metric system, first divide your height in centimeters by 100 to obtain height in meters; then divide your weight in kilograms by height in meters squared to determine BMI.
Interpretation
A BMI below 18.5 places you in the underweight category. You may be at risk of certain health conditions, such as poor nutrition, osteoporosis and fertility problems. Consider your BMI normal if it falls between 18.5 and 24.9. Your body fat is likely in the healthy range; however, your doctor can evaluate your results based on your lifestyle and family history. Discuss with your doctor a BMI of 25.0 to 29.9, which is considered overweight. If you have additional risk factors, you may benefit from a weight loss plan. Discuss with your doctor a BMI higher than 30.0, which indicates obesity.
Other Factors
When interpreting the health implications of your BMI measurement, your doctor should take into account several other factors, including your blood pressure, LDL and HDL cholesterol levels, triglyceride levels and blood glucose measurements. High values for these tests predispose you to weight-related illnesses. Physical inactivity, cigarette smoking and a family history of premature heart disease also increase your risk.
Limitations
BMI measurement can be done for both men and women, but keep in mind that it is meant to be a screening tool only. Your doctor can perform more direct measurements of body fat. The BMI formula has some limitations. In athletes and people with a very muscular build, the BMI calculation may overestimate body fat and cause them to fall in the overweight range. In addition, older adults tend to have lower muscle mass, and the BMI calculation may underestimate body fat.
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