Introduction
Body mass index, commonly referred to as BMI, is a measure of adiposity, or "fatness," based on the height and weight of the individual. It is the most widely used measure of weight problems such as obesity because of the simplicity of measurement and calculation. This provides medical and fitness professionals with a simplified means to discuss weight control factors such as obesity with patients and clients.
The formula for determining BMI has been attributed to a Belgian scientist named Adolphe Quetelet. He developed the equation at some time between 1830 and 1850.
While the equation itself was developed in the mid-nineteenth century, the term "body mass index" and the popularity of the index as a statistical and clinical tool did not rise until 1972. Dr. Ancel Keys, a professor at the University of Minnesota, established the Laboratory of Physiological Hygiene.
Dr. Keys determined BMI to be the best alternative to actually determining body fat percentile. Following the release of his paper in 1972, BMI has come to be both used and abused by health care and fitness providers throughout the United States.
The Basics
The key to BMI is determining your personal index. The formula is weight in pounds divided by height in inches (squared). The BMI for a man who stands 5 feet 11 inches tall and weighs 205 lb. would be determined as 28.6. A simpler method for determining BMI exists in the use of BMI calculators, such as those found at the National Institutes of Health and Centers for Disease Control websites.
The BMI, expressed simply as a number, is relatively useless. To have any application to the individual, it must be assigned a value. The World Health Organization (WHO) currently considers the following values to be valid:
* 18.5 to 25.0 is considered within the optimal range.
* Less than 18.5 is considered underweight.
* Over 25.0 is considered overweight.
Applications
The most legitimate application of BMI lies in the use for comparing populations of largely sedentary individuals. Unfortunately, within the United States, the most common use of BMI is for clinical applications, to determine obesity. While BMI MAY be indicative of obesity, there are shortcomings to this use. BMI, as a solution, does not take into account such lean body mass variables as muscle mass, bone density, frame size and water weight. All of these are different from one individual to the next.
Methods of testing body-fat percentages are more valuable for individual application. Simple methods such as the waist-hip ratio and skin-fold caliper test, while error prone, are better than BMI measurements. Advanced methods, such as bioelectrical impedance analysis and the current "gold standard" method, dual X-ray absorptiometry, provide the most accurate measures of healthy body weight ratios.
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