BMI stands for body mass index, which is a measure of your body weight in relation to your height to assess the "normalcy" of your weight. The University of Kentucky's Weight, BMI and Body Fat fact sheet states that as BMI increases, so does the risk for some diseases like heart disease, high blood pressure, diabetes and some cancers.
Calculating BMI
The formula for BMI is a simple one. First, multiply your body weight in pounds by 703. Then, multiply your height in inches by your height in inches. Finally, divide your new body weight number by your height number. This number is your body mass index. A BMI of 24 or below is considered desirable, with higher numbers considered overweight or obese.
Evaluation
You are categorized as overweight with a BMI of 25 to 29.9 and obese with a BMI of 30 or above. This measure is associated with mortality and an increased risk of disease. A study on body mass index and mortality in the October 7, 1999 issue of "New England Journal of Medicine" showed that among white men and women with the highest BMI, relative death risk was 2.58 (men) and 2.00 (women) and black men and women were 1.35 and 1.21 respectively, compared to 1.0 for lower BMI counterparts.
Limitations
BMI does not measure body fat or muscle and it fails to take into consideration the distribution of fat on the body. This can often classify someone as overweight or obese who is lean and muscular, which will increase the overall body weight but not increase body fat. This is especially true for athletes, bodybuilders and weightlifters.
BMI for Children
Measuring BMI for children is different from adults because children are still growing and that boys and girls develop at different rates. BMI for children age 2 to 20 compares their height and weight with their growth charts, and compares them to children of the same sex and age, according to NHLBI. BMI for children is used to screen for overweight, healthy weight or underweight and is only a tool for predicting weight issues.
Body Composition
The use of BMI as an indicator of fatness is limited in that it does not differentiate between muscle weight and fat weight. There are other factors that can affect your weight, such as the weight of our bones, organs and even blood volume. BMI is not always the best indicator, especially if you are very muscular. Getting a measure of the amount of body fat is a more effective tool in considering the risk of disease and should be considered, along with BMI, in determining your risk.
References
- "Exercise Physiology, Energy Nutrition, and Human Performance. Fifth Edition"; William D. McArdle, Frank I Katch, Victor L. Katch; 2001
- University of Kentucky: Weight, BMI and Body Fat
- Stanford University: Body Mass Index
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