Article - Measuring Obesity

How Are Overweight and Obesity Defined?

The body mass index (BMI) is the most popular tool for defining what is healthy weight, overweight and obesity today. The BMI is calculated by multiplying weight in pounds by 703 and then dividing by the height in inches squared. This approximates BMI in kg/m2. The 1998 Clinical Guidelines on the Identification, Evaluation and Treatment of Overweight and Obesity in Adults, developed by the National Heart, Lung and Blood Institute, recommend the following classifications for BMI:

• Underweight - BMI less than 18.5
• Normal weight - BMI 18.5 to 24.9
• Overweight - BMI 25 to 29.9
• Obesity - BMI 30 to 34.9 (Class 1)
• Obesity - BMI 35 to 39.9 (Class 2)
• Extreme Obesity - BMI greater than 40 (Class 3)

BMI does not actually measure body fat, but generally correlates well with the degree of obesity. For example, a person who is 5 feet, 7 inches tall and weighs 150 pounds would have a BMI of 23, well out of the range of obesity. A person of the same height and weighing 200 pounds would have a BMI of 31 and would be considered obese. BMI charts are widely available.

Often, a 10 to 15% reduction in an obese person's body weight can bring about a significant reduction in the person's health risk from obesity. This "healthy" weight loss does not always equate with a person's "cosmetic" weight loss goals.

How is Obesity and Health Risk Measured?

Currently, several different measures are used to evaluate a patient's weight status and potential health risk. However, a complete evaluation includes assessments of a person's age, height and weight, fat composition and distribution, and the presence or absence of other health problems and risk factors.

Height-weight tables indicating "ideal" weight have been in use since 1959 but have their shortcomings. A newer measure of obesity that is gaining in popularity among researchers and clinicians is the body mass index (BMI). BMI is the body weight in kilograms divided by the square of the height in meters ([weight in kg] ÷ [height in meters]2). BMI does not actually measure body fat, but generally correlates well with the degree of obesity. The categories of obesity developed by the World Health Organization are:

• BMI 25 to 29.9 - Grade 1 obesity (moderate overweight)
• BMI 30 to 39.9 - Grade 2 obesity (severe overweight)
• BMI > 40 - Grade 3 obesity (massive/morbid obesity).

Using a BMI table, a person 5'6" tall weighing 140 pounds would have a BMI of 23, well out of the range of risk. That same 5'6" person weighing 190 pounds would have a BMI of 31, in the range of Grade 2 obesity.

A BMI of 27 or higher is associated with increased morbidity and mortality; this is generally considered the point at which some form of treatment for obesity is required. A BMI between 25 and 27 is considered a warning sign and may warrant intervention, especially in the presence of additional risk factors.

The Boswell Center is headed by Dr. Kelly Boswell, a leading provider of psychology services in North Florida and an expert in the treatment and prevention of obesity and eating disorders. The Center offers personalized treatment and follow-up processes that are second to none, with a full spectrum of services, including registered dietitians.

For more information, call (904) 332-9100.

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