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.
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.
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.
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.
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.
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.
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.
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:
Do
You Know the Health Risks of Being Overweight?
Gastrointestinal
Surgery
Weight
Loss for Life
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.
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.
For
more information: http://www.niddk.nih.gov
NIH Publication No. 01-3680
October 2001
