Today, 66 percent of adults in the United States are considered 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 considered to be obese and the serious health
risks that come with it make understanding its causes and treatment crucial.
This document 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 considered 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?
"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 considered 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.
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.
You can use the above table to determine your BMI. Find your height in the
left-hand column labeled "Height." Move across to your weight. The number at the
top of the column is the BMI for that height and weight. Pounds have been rounded off.
A BMI of 25 to 29.9 is considered 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.
Body fat distribution
Health care professionals 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 socioeconomic
status and obesity has not been conclusively established, and recent research
shows that obesity is also increasing among high-income groups.
Cultural factors
An individual’s cultural background may also play a role in his or her
weight. For instance, foods specific to certain cultures that are prepared with
a lot of fat or salt may hamper one’s weight-loss efforts. Similarly, family
gatherings offering large amounts of food may make it difficult to pay attention
to proper portion control and serving sizes. Lastly, research has shown that
individuals originally from countries other than the United States have
difficulty adjusting to the calorie-rich foods offered here. These individuals
may not be able to prepare food with the ingredients they would use in their
native countries.
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 healthier ways to make your favorite foods.
- 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.
- Have a healthy snack an hour or two before a social gathering to prevent
overeating. Mingle and talk between bites to prevent eating too much too
quickly.
- 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.
- Pay attention to why you are eating. Determine if you are eating because
you are actually hungry or because you are bored, depressed, or lonely.
- 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 considered obese are more likely than non-obese men to
develop cancer of the colon, rectum, or prostate. Women who are considered obese
are more likely than non-obese 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 professionals 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 may make people considered
overweight feel unattractive.
Many people think that individuals who are considered obese are gluttonous,
lazy, or both. This is not true. As a result, people who are considered 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 professionals 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 considered 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 healthier
foods 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 adulthood. Individuals who were previously considered overweight and
obese individuals are encouraged to get 60 to 90 minutes of exercise a day to
sustain weight loss.
Although most adults do not need to see their health care 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.
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
Internet: www.win.niddk.nih.gov
The Weight-control Information Network (WIN) is a service of the National
Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) of the National
Institutes of Health
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
Source: National Institutes of Health, National
Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 11/30/08...#5784
