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
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.
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.
Body Mass Index (BMI)
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
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.
Waist-to-hip ratio (WHR)
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.
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