Body mass index, or BMI, is a tool that uses your weight and height to estimate whether you are at a healthy weight. Health providers consider your weight normal if your BMI is between 18.5 and 24.9. According to BMI charts, you are underweight if your BMI is less than 18.5 and overweight if it is 25 or higher.
BMI and Muscle
Since weight and height are the only measurements used to calculate BMI, you don't take muscle into consideration. For that you need a test that actually measures body fat. Since BMI doesn't measure body fat, elderly people might have a higher body fat percentage than their BMI indicates, and athletes and body builders might have lower body fat than their BMI indicates. However, for most people BMI, gives a good estimate of whether someone is at a healthy weight.
Reasons for BMI Use
BMI is a simple method to estimate whether someone is at higher risk for weight-related health conditions. Although it is not 100 percent accurate, it is inexpensive and takes very little time, making it suitable for use by doctors' offices. Most other methods for estimating body fat are a lot more time consuming and expensive, and thus not suited for screening purposes.
Other Options
Waist circumference is another way to estimate weight-related disease risk. For those who want to determine how much of their weight is from fat and how much is from muscle, underwater weighing is one of the more accurate methods, but less-expensive methods, including scales that use bioelectrical impedance and trained professionals using skin calipers, can give you an estimate that is relatively accurate of how much of your body weight is fat. The more body fat you have, the higher risk you have for obesity-related diseases.
Considerations
For now, BMI is one of the better options for a screening tool. Because it isn't accurate for everyone, doctors take more than BMI into account when determining your disease risk and whether you need to lose weight. If you fall into the overweight category and are very muscular, the higher BMI might be due just to your higher percentage of muscle. However, if you fall into the obese category, you most likely have extra body fat, according to the Centers for Disease Control and Prevention.
References
- Health Services at Columbia University: The Body Mass Index (BMI) and Being Overweight; July 09, 1999
- Centers for Disease Control and Prevention: About BMI for Adults; Feb. 15, 2011
- National Heart Lung and Blood Institute: Assessing Your Weight and Health Risk
- Georgia State University: Body Composition; J. Andrew Doyle, Ph.D.; March 18, 1998
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