The Body Mass Index, or BMI, is a measure of weight relative to height. It is widely used as a predictor of body fat and as a screening tool to identify potential weight problems and other health risks. BMI is calculated by dividing weight in kilograms by height in meters squared, or weight in pounds by height in inches squared and then multiplying that result by 703. The resulting number is classified into one of four different categories: underweight, normal, overweight or obese. The recommended BMI is one in the normal range, which is between 18.5 and 24.9.
Reasoning for BMI
As BMI increases into the overweight and obese categories, so does the risk for cardiovascular diseases, high blood pressure, stroke, some types of cancer and diabetes. For the general population, the BMI is a reliable indicator of risk, and is inexpensive and easy to use. It is also an easy way for doctors and caregivers to compare weight status of patients to the general population.
Categories
The BMI is classified into four different categories. Those with a BMI of 18.5 or below fall into the underweight category. The normal range for BMI is between 18.5 and 24.9. The overweight category contains BMI scores between 25 and 29.9. Those with a BMI score of 30 and above will be in the obese category. People in this category are at the highest risk for obesity-related diseases.
Recommended Range
According to Steven Aldana, professor of exercise science at Brigham Young University, "the fewest chronic diseases and deaths are found among those with ideal body weight." People with a BMI that falls within the normal range will have the lowest risk for obesity-related diseases.
Limitations
BMI is not a direct measure of body fat or body composition. It is an estimate and therefore has limitations. For example, BMI may overestimate body fat of well-trained athletes, such as football players, weight lifters and heavier wrestlers. The BMI formula is also limited because it does not take into account race, gender or age. Because of this, it may underestimate body fat in older people who have lost muscle mass.
Considerations
According to the Centers for Disease Control and Prevention, BMI is only one way to measure obesity-related disease risk and estimate body fat. Other assessments should be done to determine other risk factors for obesity-related diseases. Some other assessments include waist circumference measure, waist-to-hip ratio, body fat percentage using skin-folds, and measuring blood pressure and cholesterol. Using more than just BMI will give a better picture of disease risk and help determine an action plan to reduce that risk.
References
- Centers for Disease Control and Prevention: Healthy Weight
- "Exercise Physiology: Energy, Nutrition, and Human Performance"; William D. McArdle, et.al.; 2007
- "The Culprit and The Cure: How Lifestyle is the Culprit Behind America's Poor Health and How Transforming that Lifestyle Can be the Cure"; Steven G. Aldana; 2005
- National Heart Lung and Blood Institute: Aim for a Healthy Weight
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