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More than 60 percent of Americans
aged 20 years and older are overweight. One-quarter
of American adults are also obese, putting them
at increased health risk for chronic diseases such
as heart disease, type 2 diabetes, high blood pressure,
stroke, and some forms of cancer.
This fact sheet provides basic information
about obesity: What is it? How is it measured? What
causes it? What are the health risks? What can you
do about it?
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| What
is obesity?
To most people, the term "obesity" means to be very
overweight. Health professionals define "overweight"
as an excess amount of body weight that includes
muscle, bone, fat, and water. "Obesity" specifically
refers to an excess amount of body fat. Some people,
such as bodybuilders or other athletes with a lot
of muscle, can be overweight without being obese.
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How is obesity
measured?
Everyone needs a certain amount of body fat for
stored energy, heat insulation, shock absorption,
and other functions. As a rule, women have more
body fat than men. Most health care providers
agree that men with more than 25 percent body
fat and women with more than 30 percent body fat
are obese.
Measuring the exact amount of a person's body
fat is not easy. The most accurate measures are
to weigh a person underwater or to use an X-ray
test called Dual Energy X-ray Absorptiometry (DEXA).
These methods are not practical for the average
person, and are done only in research centers
with special equipment.
There are simpler methods to estimate body fat.
One is to measure the thickness of the layer of
fat just under the skin in several parts of the
body. Another involves sending a harmless amount
of electricity through a person's body. Both methods
are used at health clubs and commercial weight
loss programs. Results from these methods, however,
can be inaccurate if done by an inexperienced
person or on someone with severe obesity.
Because measuring a person's body fat is difficult,
health care providers often rely on other means
to diagnose obesity. Weight-for-height tables,
which have been used for decades, usually have
a range of acceptable weights for a person of
a given height. One problem with these tables
is that there are many versions, all with different
weight ranges. Another problem is that they do
not distinguish between excess fat and muscle.
A very muscular person may appear obese, according
to the tables, when he or she is not.
In recent years, body mass index (BMI) has become
the medical standard used to measure overweight
and obesity.
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| Body
Mass Index
BMI uses a mathematical formula based on a person's
height and weight. BMI equals weight in kilograms
divided by height in meters squared (BMI = kg/m2).
The BMI table that follows has already calculated
this information.
Although the BMI ranges shown in the
table are not exact ranges of healthy and unhealthy
weight, they are useful guidelines. A BMI of 25
to 29.9 indicates a person is overweight. A person
with a BMI of 30 or higher is considered obese.
Like the weight-to-height table, BMI
does not show the difference between excess fat
and muscle. BMI, however, is closely associated
with measures of body fat. It also predicts the
development of health problems related to excess
weight. For these reasons, BMI is widely used by
health care providers.
Find your weight on the bottom of
the graph. Go straight up from that point until
you come to the line that matches your height. Then
look to find your weight group.
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Body Fat
Distribution: "Pears" vs. "Apples"
Health care providers are concerned not only with
how much fat a person has, but also where the
fat is located on the body. Women typically collect
fat in their hips and buttocks, giving them a
"pear" shape. Men usually build up fat around
their bellies, giving them more of an "apple"
shape. Of course some men are pear-shaped and
some women become apple-shaped, especially after
menopause. If you carry fat mainly around your
waist, you are more likely to develop obesity-related
health problems. Women with a waist measurement
of more than 35 inches or men with a waist measurement
of more than 40 inches have a higher health risk
because of their fat distribution.
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| Causes
of Obesity
In scientific terms, obesity occurs when a person
consumes more calories than he or she burns. What
causes this imbalance between calories in and calories
out may differ from one person to another. Genetic,
environmental, psychological, and other factors
may all play a part.
Genetic factors
Obesity tends to run in families,
suggesting a genetic cause. Yet families also share
diet and lifestyle habits that may contribute to
obesity. Separating these from genetic factors is
often difficult. Even so, science shows that heredity
is linked to obesity.
In one study, adults who were adopted
as children were found to have weights closer to
their biological parents than to their adoptive
parents. In this case, the person's genetic makeup
had more influence on the development of obesity
than the environment in the adoptive family home.
Environmental factors
Genes do not destine people to a lifetime of obesity,
however. Environment also strongly influences obesity.
This includes lifestyle behaviors such as what a
person eats and his or her level of physical activity.
Americans tend to eat high-fat foods, and put taste
and convenience ahead of nutrition. Also, most Americans
do not get enough physical activity.
Although you cannot change your genetic makeup,
you can change your eating habits and levels of
activity. Try these techniques that have helped
some people lose weight and keep it off:
- Learn how to choose more nutritious meals that
are lower in fat.
- Learn to recognize and control environmental
cues (like inviting smells) that make you want
to eat when you're not hungry.
- Become more physically active.
- Keep records of your food intake and physical
activity.
Psychological factors
Psychological factors may also influence
eating habits. Many people eat in response to negative
emotions such as boredom, sadness, or anger.
Most overweight people have no more
psychological problems than people of average weight.
Still, up to 10 percent of people who are mildly
obese and try to lose weight on their own or through
commercial weight loss programs have binge eating
disorder. This disorder is even more common in people
who are severely obese.
During a binge eating episode, people
eat large amounts of food and feel that they cannot
control how much they are eating. Those with the
most severe binge eating problems are also likely
to have symptoms of depression and low self-esteem.
These people may have more difficulty losing weight
and keeping it off than people without binge eating
problems.
If you are upset by binge eating behavior
and think you might have binge eating disorder,
seek help from a health professional such as a psychiatrist,
psychologist, or clinical social worker.
Other causes
of obesity
Some illnesses can lead to obesity or a tendency
to gain weight. These include hypothyroidism, Cushing's
syndrome, depression, and certain neurological problems
that can lead to overeating. Also, drugs such as
steroids and some antidepressants may cause weight
gain. A doctor can tell whether there are underlying
medical conditions that are causing weight gain
or making weight loss difficult.
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| Consequences
of Obesity
Health Risks
Obesity is more than a cosmetic problem;
it is a health hazard. Approximately 280,000 adult
deaths in the United States each year are related
to obesity. Several serious medical conditions have
been linked to obesity, including type 2 diabetes,
heart disease, high blood pressure, and stroke.
Obesity is also linked to higher rates of certain
types of cancer. Obese men are more likely than
non-obese men to die from cancer of the colon, rectum,
or prostate. Obese women are more likely than non-obese
women to die from cancer of the gallbladder, breast,
uterus, cervix, or ovaries.
Other diseases and health problems
linked to obesity include:
- Gallbladder disease and gallstones.
- Liver disease.
- Osteoarthritis, a disease in which the joints
deteriorate. This is possibly the result of
excess weight on the joints.
- Gout, another disease affecting the joints.
- Pulmonary (breathing) problems, including
sleep apnea in which a person can stop breathing
for a short time during sleep.
- Reproductive problems in women, including
menstrual irregularities and infertility.
Health care providers generally agree
that the more obese a person is, the more likely
he or she is to develop health problems.
Psychological and social
effects
Emotional suffering may be one of
the most painful parts of obesity. American society
emphasizes physical appearance and often equates
attractiveness with slimness, especially for women.
Such messages make overweight people feel unattractive.
Many people think that obese individuals
are gluttonous, lazy, or both, even though this
is not true. As a result, obese people often face
prejudice or discrimination in the job market, at
school, and in social situations. Feelings of rejection,
shame, or depression are common.
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| Who
should lose weight?
Health care providers generally agree that people
who have a BMI of 30 or more can improve their health
through weight loss. This is especially true for
people who are severely obese.
Preventing additional weight gain
is recommended if you have a BMI between 25 and
29.9, unless you have other risk factors. Obesity
experts recommend you try to lose weight if you
have two or more of the following:
- Family history of certain chronic
diseases. If you have close relatives
who have had heart disease or diabetes, you
are more likely to develop these problems if
you are obese.
- Pre-existing medical conditions.
High blood pressure, high cholesterol levels,
or high blood sugar levels are all warning signs
of some obesity-associated diseases.
- "Apple" shape. If your weight
is concentrated around your waist, you may have
a higher risk of heart disease, diabetes, or
cancer than people of the same weight who have
a "pear" shape.
Fortunately, a weight loss of 5 to
10 percent can do much to improve health by lowering
blood pressure and cholesterol levels. In addition,
recent research has shown that a 5- to 7-percent
weight loss can prevent type 2 diabetes in people
at high risk for the disease.
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| How is obesity treated?
The method of treatment depends on your level of
obesity, overall health condition, and motivation
to lose weight. Treatment may include a combination
of diet, exercise, behavior modification, and sometimes
weight-loss drugs. In some cases of severe obesity,
gastrointestinal surgery may be recommended. Remember,
weight control is a life-long effort.
For more information on health risks,
treatment options, and binge eating, click on these
links to WIN publications:
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| Additional
Reading
Allison DB, Fontaine KR, Manson JE, Stevens
J, VanItallie TB. Annual deaths attributable to
obesity in the United States. Journal of the
American Medical Association; 1999;282(16):1530-1538.
National Heart, Lung, and Blood Institute.
Clinical Guidelines on the Identification, Evaluation,
and Treatment of Overweight and Obesity in Adults.
Department of Health and Human Services, National
Institutes of Health; 1998. NIH Publication No.
98-4083.
National Task Force on Prevention
and Treatment of Obesity. Overweight, obesity, and
health risk. Archives of Internal Medicine.
2000;160(7):898-904.
Partnership for Healthy Weight Management.
Weight Loss: Finding a Weight Loss Program that
Works for You. 2000. Phone: 1-888-8-PUEBLO. Website:
www.consumer.gov/weightloss/brochures.htm.
Partnership for Healthy Weight Management.
Setting Goals for Healthy Weight Loss. 1999. Phone:
1-888-8-PUEBLO. Website: www.consumer.gov/weightloss/brochures.htm.
The President’s Council on Physical
Fitness and Sports, Department of Health and Human
Services. Exercise and Weight Control. Website:
www.fitness.gov/Reading_Room/reading_room.html.
U.S. Department of Agriculture and
U.S. Department of Health and Human Services. Dietary
Guidelines for Americans. 2000. Phone: 1-888-878-3256.
Website: www.usda.gov/cnpp
or www.health.gov/dietaryguidelines.
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Weight-control
Information Network
1 WIN WAY
BETHESDA, MD 20892-3665
Phone: (202) 828-1025
FAX: (202) 828-1028
E-mail: win@info.niddk.nih.gov
Internet: www.niddk.nih.gov/health/nutrit/nutrit.htm
Toll-free number: 1-877-946-4627
The Weight-control Information Network (WIN) is
a national service of the National Institute of
Diabetes and Digestive and Kidney Diseases of the
National Institutes of Health, which is the Federal
Government's lead agency responsible for biomedical
research on nutrition and obesity. Authorized by
Congress (Public Law 103-43), WIN provides the general
public, health professionals, the media, and Congress
with up-to-date, science-based health information
on weight control, obesity, physical activity, and
related nutritional issues.
WIN answers inquiries, develops and distributes
publications, and works closely with professional
and patient organizations and Government agencies
to coordinate resources about weight control and
related issues.
Publications produced by WIN are carefully reviewed
by both NIDDK scientists and outside experts. This
fact sheet was also reviewed by Thomas Wadden, Ph.D.,
Director, Weight and Eating Disorders Program, University
of Pennsylvania, and Goulda Downer, Ph.D., President,
Metroplex Health and Nutrition Services.
This e-text is not copyrighted.WIN encourages unlimited
duplication and distribution of this fact sheet. |
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