Being overweight or having a high percentage of body fat increases the risk of developing chronic and life-threatening diseases. To help identify patients at risk, health care professionals have tools to help determine when a patient may develop weight-related health problems. One of these tools is body mass index. While BMI should not be the only diagnostic tool, it has been shown to be a reliable indicator of disease risk and life expectancy when used as part of a total assessment plan.
Identification
For adults, BMI is calculated using current weight and height and it is used to identify if you are either overweight or obese. For adults, BMI is calculated by dividing weight in pounds by height in inches, squared. You then multiply the answer by a conversion factor of 703. A BMI of 18.5 to 24.9 is considered normal, between 25 and 29.9 is considered overweight and once it reaches 30 or greater, you're considered obese. If BMI climbs to 40 or higher, you're classed as morbidly obese and at a very high risk of disease. Children are different and a physician should diagnose a weight problem for those 18 and younger.
Benefits
Body mass index does not measure percent body fat directly, but it is considered a fairly reliable indicator of body fatness for most people, reports the Centers for Disease Control and Prevention. It is considered a screening tool, not a diagnostic tool. Health professionals use BMI because measuring body fat directly and accurately often requires expensive equipment. In addition, the accuracy of the results depends on the experience of the tester. Calculating body mass index is simpler way to identify who may need further evaluation.
Limitations
Because body mass index does not directly measure percent body fat, it is not always accurate. Athletic individuals with a high percent of muscle mass may have a high BMI but low percent body fat. These individuals would be wrongly classified as overweight using BMI. However, in most cases individuals who have a body mass index of 30 or higher tend to be obese. Individuals who are older or deconditioned may have a low percent of muscle mass. BMI may be within the normal or just slightly overweight range, but they could be at a high risk for disease due to a high percent body fat.
Considerations
Body mass index should always be used alongside other screening tools to fully determine an individual's risk for disease. Percent body fat can be measured directly and an individual's diet and exercise habits also play a role. Blood pressure and cholesterol readings should also be taken into consideration. In addition, if you're carrying a high percentage of excess fat in the abdomen there is a higher risk of chronic disease than having excess fat in other areas. Given this, taking waist circumference is also considered a useful tool, especially when used in combination with BMI. Waist circumference is considered most beneficial in individuals with a BMI of 25 to 34, however for those whose BMI climbs to 35 or above, waist circumference does not adjust disease risk that much, states the University of Illinois.
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