For many years the definition of obesity was objectified with height and weight charts that offered ranges of healthy weight based on age, height, weight, and gender. But several versions of the chart existed skewing an exact standard for the definition of obesity

Body fat tests measured the percentage of body fat but were not precise. The best body fat measurements were done underwater and highly inconvenient. Other body fat tests include the skin fold test, where the skin is grabbed and measured in calipers, and the bioelectric impedance analysis, which measure fat through an electric current.

Current definitions of obesity rely on a measure called the Body Mass Index, or BMI. The BMI, which is calculated with height and weight measurements, has come to be the most internationally accepted definition of obesity.

To calculate your BMI determine your height in inches and multiply it by itself (ex. 64 x 64 = 4096). Divide your weight in pounds by your height calculation (ex. 175 / 4096 = 0.04272); then multiply this result by 703 (ex. 0.04272 x 703 = 30). This should give you your BMI.

A person with a body mass index exceeding 30 is considered obese, and someone with a BMI of 40 or more has morbid obesity. Morbid obesity refers to a dangerous condition in which the sufferer is at risk of physical disability and a severely impaired quality of life. The table below further illustrates the classifications of BMI.

In 1997, the National Institutes of Health changed the definition of "overweight" and "obese." Consequently, millions of Americans went to bed with average bodies and woke up as part of the growing obesity epidemic, all without gaining a pound. Using the old definitions, America had 68 million people who were considered overweight or obese. Under the new definitions, 96 million Americans now fall into this category.

Some controversy exists over the accuracy of the BMI for setting obesity standards. Because the BMI uses a standard weight against height formula, it doesn't take into account whether the weight is fat or muscle. Other criticisms of the BMI method of assessing weight and health are that it does not account for:

Determining waist circumference eliminates the inconsistencies of the BMI. Waist circumference measurement is an important part of determining obesity and morbid obesity. A waist circumference of 40 inches in men and 35 inches in women is an indication of obesity.

Waist to hip ratio is also used as a guideline for determining obesity. This measurement determines how weight is distributed on the body. Weight distribution on the lower half of the body (pear-shape) generally does not pose the same serious consequences as weight that crowds the abdominal area. Hip to waist ratio is calculated by dividing the circumference of the waist by the circumference of the hips. A healthy waist to hip ratio for women is 0.80 or less. For men, 0.90 or less is a healthy waist to hip ratio. Anything over 1.0 is considered obese.

Resources

Balko, R. (2004, October 7). The BMI problem. Risk: Regulation and Reality Conference, Toronto, ON, Canada.

Centers for Disease Control and Prevention (CDC). (updated 2004). Defining overweight and obesity.

CNN. (1998, June 17). Who's fat? New definition adopted.

Cook-Euell, V. (2005, March 3). Paul Campos blows the whistle on America's unhealthy obsession with weight in a new book—" The Obesity Myth". PRWeb.

Haggerty, M. (1999). Obesity. Gale Encyclopedia of Medicine.

National Institute of Diabetes and Digestive and Kidney Diseases—Weight-Control Information Network. (2001, October). Understanding adult obesity [NIH Publication No.01-3680].

National Library of Medicine. (updated 2001). Morbid obesity. MedlinePlus Medical Encyclopedia.