Body mass index (BMI) is used to calculate body weight relative to height to determine if an individual is underweight, overweight or within a healthy weight range. Even though it does not take body fat percentage into account, the BMI measurement is still one of the most widely accepted determinants for a person's overall health and weight status. BMI assesses how much an individual's body weight departs from what is normal or desirable for a person of his height.
History of BMI
The BMI calculation was created by Belgian mathematician Lambert Adolphe Jacques Quételet, who published a study of the average man in 1835 entitled, "A Treatise on Man and the Development of His Faculties." It wasn't until the 1970s, however, that American health researcher Ancel Keys coined the phrase "body mass index." BMI was explicitly cited by Keys as being appropriate for group population studies and not for individual diagnosis. Nevertheless, because of its simplicity, the BMI quickly became the common way to measure an individual's weight relative to his height. BMI is still used daily by physicians, trainers and even insurance agencies to screen and test patients.
The BMI Formula
Follow this formula to get a rating: First, convert height to inches. For example, a person who stands 6 feet 2 inches is 74 inches tall. Next, square the height in inches (74 x 74 = 5,476). Then, divide body weight by the squared height (210 lbs./5,476 = 0.0383). Multiply the number by 703 to obtain your BMI rating (0.0383 x 703 = 26.9 BMI).
BMI Ratings
The Centers for Disease Control and Prevention (CDC) uses weight and health standards: Any person with a BMI below 18.5 is considered underweight. Persons with a BMI between 18.5 and 24.9 are considered normal weight. Those with a BMI between 25.0 and 29.9 are considered overweight. Anyone with a BMI over 30.0 is considered obese.
BMI Limitations
The BMI formula is a simple and inexpensive method of screening for weight, but it has many limitations. BMI does not take into account age, gender and family history. It also doesn't factor in body fat mass. As a result, many athletes with large lean muscle mass will have an "overweight" BMI even though they don't have a high body fat percentage. Another limitation is that women tend to have more body fat than men with the same BMI, and older people tend to have more body fat than young adults.
Improve Health Beyond BMI
Health professionals need to do further assessments to fully evaluate health risks. These tests would include measurements of body fat percentage, waist circumference, diet history, exercise patterns and family history. Patients also must continue to be an advocate for their own health. Obtain regular exercise to lower weight and increase lean muscle mass, make healthy food choices that consist mostly of whole non-processed foods and receive regular physical examinations from a primary health care physician.
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