Body mass index, or BMI, is a screening tool that provides a reasonable estimation of your body's fat percentage. There are limitations for its use. According to the Centers for Disease Control and Prevention, your BMI does not diagnose any health condition but rather screens you for your risk of weight-related diseases, such as heart disease, diabetes and certain cancers.
Define your BMI
Your BMI is a ratio of your weight to your height. Since BMI calculation uses kilograms and meters, the University of Idaho, Department of Food and Science Toxicology says to multiply your weight by 0.45 and your height by 0.25 to account for the conversion factor. For instance, if you weigh 125 pounds and are 63 inches tall, multiply 125 by 0.45 for your weight, and 63 by 0.25 for your height, which gives you 56.25 kilograms and 1.575 meters. Divide 56.25 by 1.575 squared. The total is 22.7, which is your BMI number.
Considerations
Some health or fitness professionals may place more importance on body fat content than others do. For instance, a doctor may use the following to determine an ideal weight: females would add five pounds--and men would add 6 pounds--to 100 pounds for every inch over five feet. If you are within a few pounds of your ideal weight, your doctor may not place much importance on your exact body fat percentage. Contrarily, a personal trainer is interested in your exact percentage to help you lose fat pounds and gain muscle mass.
Expert Insight
A BMI does not discriminate between muscle and fat weight. Because muscle weighs more than fat, a BMI may not accurately reflect body fat percentage. Peter Katzmarzyk, an associate executive director of population science at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, says fat percentage is more important than how much you weigh. He also recommends using a BMI calculator over using other methods of finding your body fat percentage.
Limitations and Professional Use
Your BMI is a marker used by a variety of health care professionals. For instance, a dietitian may collaborate with your doctor when planning your diet. The dietitian may use your BMI to calculate your caloric requirements, but she also addresses other dietary needs indicated by your doctor. With your cooperation, your dietitian will also consider using foods you like that meet your dietary requirements. This process of designing your diet--using your BMI as a starting point--is a science and an art. This means there are limitations--albeit some freedoms and liberation--for its use.
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