Overweight and Obesity

Defining Overweight and Obesity

Overweight and Obesity Among Adults

Recent results of the National Health and Nutrition Examination Survey (NHANES) 1999 indicate that an estimated 61 percent of U.S. adults are either overweight or obese, defined as having a body mass index (BMI) of 25 or more.

• Among U.S. adults aged 20-74 years, the prevalence of overweight (defined as BMI 25.0-29.9) has increased an estimated 2 percent since 1980, increasing from 33 percent to the 35 percent of the population in 1999 (based on NHANES II and NHANES 1999 data).
• In the same population, obesity (defined as BMI greater than or equal to 30.0) has nearly doubled from approximately 15 percent in 1980 to an estimated 27 percent in 1999.

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

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.

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

• The percentage of children and adolescents who are defined as overweight has more than doubled since the early 1970s.
• About 13 percent of children and adolescents are now seriously overweight.

In spite of the public health impact of obesity and overweight, these conditions have not been a major public health priority in the past. Halting and reversing the upward trend of the obesity epidemic will require effective collaboration among government, voluntary, and private sectors, as well as a commitment to action by individuals and communities across the nation.

BMI is a common measure expressing the relationship (or ratio) of weight-to-height. It is a mathematical formula in which a person's body weight in kilograms is divided by the square of his or her height in meters (i.e., wt/(ht)2. The BMI is more highly correlated with body fat than any other indicator of height and weight (NRC p563).

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

What BMI levels are risky?

According to the NIH Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, all adults (aged 18 years or older) who have a BMI of 25 or more are considered at risk for premature death and disability as a consequence of overweight and obesity. These health risks increase even more as the severity of an individual's obesity increases.

Waist circumference is a common measure used to assess abdominal fat content. The presence of excess body fat in the abdomen, when out of proportion to total body fat, is considered an independent predictor of risk factors and ailments associated with obesity.

What waist size is risky? Undesirable waist circumferences differ for men and women.

• Men are at risk who have a waist measurement greater than 40 inches (102 cm)
• Women are at risk who have a waist measurement greater than 35 inches (88 cm)

Note: If a person has short stature (under 5 feet in height) or has a BMI of 35 or above, waist circumference standards used for the general population may not apply.

How to measure waist circumference

With a tape measure, comfortably measure the distance around the smallest area below the rib cage and above the umbilicus (belly button).

How to measure hip circumference

With a tape measure, comfortably measure the distance around the largest extension of the buttocks.

Waist-to-hip ratio (WHR) is the ratio of a person's waist circumference to hip circumference, mathematically calculated as the waist circumference divided by the hip circumference. For most people, carrying extra weight around their middle increases health risks more than carrying extra weight around their hips or thighs. (NOTE: Overall obesity is still more risky than body fat storage locations or waist-to-hip ratio.)

What waist-to-hip ratio is considered risky?

For both men and women, a waist-to-hip ratio of 1.0 or higher is considered "at risk" or in the danger zone for undesirable health consequences, such as heart disease and other ailments connected with being overweight.

What is a good waist-to-hip ratio?

For men, a ratio of .90 or less is considered safe. For women, a ratio of .80 or less is considered safe.

References

Stunkard AJ, Wadden TA. (Editors) Obesity: theory and therapy, Second Edition. New York: Raven Press, 1993.

National Research Council. Diet and health: implications for reducing chronic disease risk. Washington, DC: National Academy Press, 1989.

National Institutes of Health. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults. Bethesda, Maryland: Department of Health and Human Services, National Institutes of Health, National Heart, Lung, and Blood Institute, 1998.

This page last updated September 05, 2002. Courtesy of United States Department of Health and Human Services.
Centers for Disease Control and Prevention. National Center for Chronic Disease Prevention and Health Promotion. Division of Nutrition and Physical Activity.

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