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WIN - Publication - Understanding Obesity
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(307KB)
What is obesity?
How is obesity
measured?
Body Mass Index
Body Fat
Distribution
What causes obesity?
Genetic
Factors
Environmental
and Social Factors
Other Causes of
Obesity
What are the
consequences of obesity?
Health
Risks
Psychological and
Social Effects
Who should lose
weight?
How is obesity
treated?
Additional
Reading
Today, more than 65 percent of s in the
United States are overweight or obese. Obesity puts
people at increased risk for chronic diseases such
as heart disease, type 2 diabetes, high blood
pressure, stroke, and some forms of cancer.
The large number of people with obesity and the
serious health risks that come with it make
understanding its causes and treatment crucial.
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?
What is
obesity?
"Obesity" specifically refers to an
excessive amount of body fat. "Overweight" refers
to an excessive amount of body weight that includes
muscle, bone, fat, and water. As a rule, women have
more body fat than men. Most health care
professionals agree that men with more than 25
percent body fat and women with more than 30
percent body fat are obese. These numbers should
not be confused with the body mass index (BMI),
however, which is more commonly used by health care
professionals to determine the effect of body
weight on the risk for some diseases.
How is obesity
measured?
Measuring the exact amount of
a person's body fat is not easy. The most
accurate measures are to weigh a person
underwater or in a chamber that uses air
displacement to measure body volume, or to use an
X-ray test called Dual Energy X-ray
Absorptiometry, also known as 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. Results from these methods,
however, can be inaccurate if done by an
inexperienced person or on someone with extreme
obesity.
Because measuring a person's
body fat is difficult, health care professionals
often rely on other means to diagnose obesity.
Weight-for-height tables, used for decades, 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.
According to the tables, a very muscular person
may be classified obese when he or she is not.
The BMI is less likely to misidentify a person's
appropriate weight-for-height range.
Body Mass
Index
The BMI is a tool
used to assess overweight and obesity and monitor
changes in body weight. Like the weight-for-height
tables, BMI has its limitations because it does not
measure body fat or muscle directly. It is
calculated by dividing a person's weight in pounds
by height in inches squared and multiplied by
703.
Two people can
have the same BMI but different body fat
percentages. A bodybuilder with a large muscle mass
and low percentage of body fat may have the same
BMI as a person who has more body fat. However, a
BMI of 30 or higher usually indicates excess body
fat.
The BMI table
below provides a useful guideline to check your
BMI. First, 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. A BMI of
25 to 29.9 indicates a person is overweight. A
person with a BMI of 30 or higher is considered
obese. Please review your findings with your health
care provider if your BMI is outside of the normal
range.
* Without Shoes
**Without Clothes
Sources
George
Bray, M.D., Pennington Biomedical Research
Center.
National Heart, Lung, and Blood Institute’s
Clinical Guidelines on the Identification,
Evaluation, and Treatment of Overweight and
Obesity in s: The Evidence
Report.
Body Fat
Distribution
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.
Excess abdominal fat is an important,
independent risk factor for disease. Research has
shown that waist circumference is directly
associated with abdominal fat and can be used in
the assessment of the risks associated with
obesity or overweight. 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 and men with a waist
measurement of more than 40 inches may have more
health risks than people with lower waist
measurements because of their body fat
distribution.
What causes
obesity?
Obesity occurs when a person consumes more calories
from food than he or she burns. Our bodies need
calories to sustain life and be physically active,
but to maintain weight we need to balance the
energy we eat with the energy we use. When a person
eats more calories than he or she burns, the energy
balance is tipped toward weight gain and obesity.
This imbalance between calories-in and calories-out
may differ from one person to another. Genetic,
environmental, and other factors may all play a
part.
Genetic
Factors
Obesity tends to run in
families, suggesting a genetic cause. However,
families also share diet and lifestyle habits that
may contribute to obesity. Separating genetic from
other influences on obesity is often difficult.
Even so, science does show a link between obesity
and heredity.
Environmental and Social
Factors
Environment strongly influences obesity.
Consider that most people in the United States
alive today were also alive in 1980, when obesity
rates were lower. Since this time, our genetic
make-up has not changed, but our environment
has.
Environment includes lifestyle behaviors such as
what a person eats and his or her level of physical
activity. Too often Americans eat out, consume
large meals and high-fat foods, and put taste and
convenience ahead of nutrition. Also, most people
in the United States do not get enough physical
activity.
Environment also includes the world around
us—our access to places to walk and healthy
foods, for example. Today, more people drive long
distances to work instead of walking, live in
neighborhoods without sidewalks, tend to eat out or
get “take out” instead of cooking, or
have vending machines with high-calorie, high-fat
snacks at their workplace. Our environment often
does not support healthy habits.
In addition, social factors including poverty
and a lower level of education have been linked to
obesity. One reason for this may be that
high-calorie processed foods cost less and are
easier to find and prepare than healthier foods,
such as fresh vegetables and fruits. Other reasons
may include inadequate access to safe recreation
places or the cost of gym memberships, limiting
opportunities for physical activity. However, the
link between low socio-economic status and obesity
has not been conclusively established, and recent
research shows that obesity is also increasing
among high-income groups.
Although you cannot change your genetic makeup,
you can work on changing your eating habits, levels
of physical activity, and other environmental
factors. Try these ideas:
Learn to choose sensible portions of
nutritious meals that are lower in fat.
Learn to recognize and control environmental
cues (like inviting smells or a package of
cookies on the counter) that make you want to eat
when you are not hungry.
Engage in at least 30 minutes of
moderate-intensity physical activity (like brisk
walking) on most, preferably all, days of the
week.
Take a walk instead of watching
television.
Eat meals and snacks at a table, not in front
of the TV.
Keep records of your food intake and physical
activity.
Other
Causes of Obesity
Some illnesses may lead to or are associated
with weight gain or obesity. These include:
Hypothyroidism, a condition in which the
thyroid gland fails to produce enough thyroid
hormone. It often results in lowered metabolic
rate and loss of vigor.
Cushing's syndrome, a hormonal disorder
caused by prolonged exposure of the body's
tissues to high levels of the hormone cortisol.
Symptoms vary, but most people have upper body
obesity, rounded face, increased fat around the
neck, and thinning arms and legs.
Polycystic ovary syndrome, a condition
characterized by high levels of androgens (male
hormone), irregular or missed menstrual cycles,
and in some cases, multiple small cysts in the
ovaries. Cysts are fluid-filled sacs.
A doctor can tell whether there are underlying
medical conditions that are causing weight gain or
making weight loss difficult.
Lack of sleep may also contribute to obesity.
Recent studies suggest that people with sleep
problems may gain weight over time. On the other
hand, obesity may contribute to sleep problems due
to medical conditions such as sleep apnea, where a
person briefly stops breathing at multiple times
during the night. (Visit
www.win.niddk.nih.gov/publications/health_risks.htm#sleep
for more information on the relationship between
sleep apnea and obesity.) You may wish to talk with
your health care provider if you have difficulty
sleeping.
Certain drugs such as steroids, some
antidepressants, and some medications for
psychiatric conditions or seizure disorders may
cause weight gain. These drugs may slow the rate at
which the body burns calories, stimulate appetite,
or cause the body to hold on to extra water. Be
sure your doctor knows all the medications you are
taking (including over-the-counter medications and
dietary supplements). He or she may recommend a
different medication that has less effect on weight
gain.
What are
the consequences of obesity?
Health
Risks
Obesity is more
than a cosmetic problem. Many 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. Men who
are obese are more likely than nonobese men to
develop cancer of the colon, rectum, or prostate.
Women who are obese are more likely than nonobese
women to develop cancer of the gallbladder, uterus,
cervix, or ovaries. Esophageal cancer has also been
associated with obesity.
Other diseases and
health problems linked to obesity
include:
Gallbladder disease and
gallstones.
Fatty liver disease (also called
nonalcoholic steatohepatitis or NASH).
Gastroesophageal reflux, or what is
sometimes called GERD. This problem occurs when
the lower esophageal sphincter does not close
properly and stomach contents leak
back—or reflux—into the
esophagus.
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, which causes a
person to 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 individuals with obesity are gluttonous, lazy,
or both. This is not true. As a result, people who
are obese often face prejudice or discrimination in
the job market, at school, and in social
situations. Feelings of rejection, shame, or
depression may occur.
Who should lose
weight?
Health
care providers generally agree that people who have
a BMI of 30 or greater can improve their health
through weight loss. This is especially
true for people with a BMI of 40 or greater, who
are considered extremely obese.
Preventing additional
weight gain is recommended if you have a BMI
between 25 and 29.9, unless you have other risk
factors for obesity-related diseases. 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.
Preexisting
medical conditions. High blood pressure, high LDL cholesterol
levels, low HDL cholesterol levels, high
triglycerides, and high blood glucose are all
warning signs of some obesity-associated
diseases.
Large waist circumference.
Men who have waist circumferences greater than
40 inches, and women who have waist
circumferences greater than 35 inches, are at
higher risk of diabetes, dyslipidemia (abnormal
amounts of fat in the blood), high blood
pressure, and heart disease.
Fortunately, a weight loss of 5 to 10
percent of your initial body weight can do much
to improve health by lowering blood pressure and
other risk factors for obesity-related diseases.
In addition, research shows that a 5- to
7-percent weight loss brought about by moderate
diet and exercise can delay or possibly prevent
type 2 diabetes in people at high risk for the
disease. In a recent study, participants who were
overweight and had pre-diabetes—a condition
in which a person’s blood glucose level is
higher than normal, but not high enough to be
classified as diabetes—were able to delay
or prevent the onset of type 2 diabetes by
adopting a low-fat, low-calorie diet and
exercising for 30 minutes a day, 5 days a week.
For more information about pre-diabetes and
diabetes, visit www.diabetes.niddk.nih.gov.
How is obesity
treated?
The method of treatment depends on
your level of obesity, overall health condition,
and readiness to lose weight. Treatment may include
a combination of diet, exercise, behavior
modification, and sometimes weight-loss drugs. In
some cases of extreme obesity, bariatric surgery
may be recommended. (Visit
www.win.niddk.nih.gov/publications/gastric.htm
for more information on bariatric surgery.)
Remember, weight control is a life-long effort, and
having realistic expectations about weight loss is
an important consideration. Eating a healthful diet
and getting at least 30 minutes of
moderate-intensity physical activity on most,
preferably all, days of the week have important
health benefits. Sixty minutes of physical activity
a day may be required to prevent gradual weight
gain in hood. Previously overweight and obese
individuals are encouraged to get 60 to 90 minutes
of exercise a day to sustain weight loss.
Although most s do not need to see their
healthcare professional before starting a
moderate-intensity physical activity program, men
older than 40 years and women older than 50 years
who plan a vigorous program or who have either
chronic disease or risk factors for chronic
illnesses should speak with their health care
provider before starting a physical activity
program.
For more information on health risks, treatment
options, and binge eating, refer to these
Weight-control Information Network (WIN)
publications:
Active at Any Size.
Available from WIN and online at
www.win.niddk.nih.gov/publications/active.htm.
National Institutes of Health (NIH) Publication No.
04-4352. April 2004.
Do You Know the Health Risks of Being
Overweight? Available from WIN and online at
www.win.niddk.nih.gov/publications/health_risks.htm.
NIH Publication No. 04-4098. November 2004.
Healthy Eating and Physical Activity Across
Your Lifespan: Better Health and You (Tips for
s). Available in English and Spanish.
Available from WIN and online at
www.win.niddk.nih.gov/publications/better_health.htm.
NIH Publication No. 04-4992. June 2004.
Just Enough for You: About Food
Portions. Available from WIN and online at
www.win.niddk.nih.gov/publications/just_enough.htm.
NIH Publication No. 03-5287. January 2003.
Weight Loss for Life. Available from
WIN and online at
www.win.niddk.nih.gov/publications/for_life.htm.
NIH Publication No. 04-3700. May 2004.
For more information on NASH, visit
www.digestive.niddk.nih.gov/ddiseases/pubs/nash/index.htm.
Additional
Reading
National Institute of Diabetes and
Digestive and Kidney Diseases. Strategic Plan
for NIH Obesity Research. U.S. Department of
Health and Human Services (DHHS); NIH. NIH
Publication No. 04-5493. 2004.
National Heart, Lung, and Blood Institute.
Clinical Guidelines on the Identification,
Evaluation, and Treatment of Overweight and Obesity
in s. DHHS; NIH. NIH Publication No.
98-4083. 1998.
National Task Force on Prevention and Treatment
of Obesity. Overweight, obesity, and health risk.
Archives of Internal Medicine.
160(7):898-904. 2000.
Partnership for Healthy Weight Management.
Weight Loss: Finding a Weight Loss Program that
Works for You.
Website:
www.consumer.gov/weightloss/brochures.htm.
2000.
U.S. Department of Agriculture and DHHS.
Finding Your Way to a Healthier You: Based on
the “Dietary Guidelines for
Americans.” Phone: 1-888-878-3256.
Website: www.healthierus.gov/dietaryguidelines.
2005.
Weight-control
Information Network
1 WIN WAY
BETHESDA, MD 20892-3665
Phone: (202) 828-1025
Toll-free number: 1-877-946-4627
FAX: (202) 828-1028
Email: win@info.niddk.nih.gov
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.
Publications produced by WIN are carefully
reviewed by both NIDDK scientists and outside
experts. This fact sheet was also reviewed by
Steven N. Blair, P.E.D., President and Chief
Executive Officer, Cooper Institute. A review was
also conducted by Domenica M. Rubino, M.D.,
Assistant Medical Director, George Washington
University Weight Management Program.
This publication is not copyrighted. WIN
encourages users of this fact sheet to duplicate
and distribute as many copies as desired.
NIH Publication
No. 01-3680
October 2001
Updated March 2006
Contact Us
Toll free: 1-877-946-4627
Fax: (202) 828-1028
E-mail: win@info.niddk.nih.gov
Weight-control Information Network, 1 WIN Way, Bethesda, MD
20892-3665
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