Overweight and Obesity Among
AdultsRecent 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.
OverweightOverweight 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 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.
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.
ReferencesStunkard 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.