Defining Overweight and Obesity

Overweight and Obesity Among Adults

Results of the National Health and Nutrition Examination Survey (NHANES) 1999-2000 indicate that an estimated 64 percent of U.S. adults are either overweight or obese, defined as having a body mass index (BMI) of 25 or more.

Overweight

Overweight refers to increased body weight in relation to height, when compared to some standard of acceptable or desirable weight (NRC p.114; Stunkard p.14). NOTE: Overweight may or may not be due to increases in body fat. It may also be due to an increase in lean muscle. For example, professional athletes may be very lean and muscular, with very little body fat, yet they may weigh more than others of the same height. While they may qualify as "overweight" due to their large muscle mass, they are not necessarily "over fat," regardless of BMI.

Desirable weight standards are derived in a number of ways:

• By using a mathematical formula known as Body Mass Index (BMI), which represents weight levels associated with the lowest overall risk to health. Desirable BMI levels may vary with age.
• By using actual heights and weights measured and collected on people who are representative of the U.S. population by the National Center for Health Statistics. Other desirable weight tables have been created by the Metropolitan Life Insurance Company, based on their client populations.

These sources are consistent with the U.S. Dietary Guidelines and with the National Heart, Lung, and Blood Institute's Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults.

Obesity

Individuals with a BMI of 25 to 29.9 are considered overweight, while individuals with a BMI of 30 or more are considered obese.

Obesity is defined as an excessively high amount of body fat or adipose tissue in relation to lean body mass. (NRC p114; Stunkard p14) The amount of body fat (or adiposity) includes concern for both the distribution of fat throughout the body and the size of the adipose tissue deposits. Body fat distribution can be estimated by skinfold measures, waist-to-hip circumference ratios, or techniques such as ultrasound, computed tomography, or magnetic resonance imaging.

Overweight and Obesity Among Children and Adolescents

• The percentage of children and adolescents who are defined as overweight has more than doubled since the early 1970s.
  
• About 15 percent of children and adolescents are now overweight.