Understanding

Adult Obesity

WIN Weight-control Information Network

Today, 66 percent of adults in the United States are considered “Obesity” specifically refers

overweight or obese. Obesity puts people at increased risk for to an excessive amount

chronic diseases such as heart disease, type 2 diabetes, high of body fat. “Overweight” blood pressure, stroke, and some forms of cancer.

refers to an excessive

The large number of people considered to be obese and the amount of body weight serious health risks that come with it make understanding its

causes and treatment crucial. This fact sheet provides basic that includes muscle, bone,

information about obesity: What is it? How is it measured? What fat, and water. As a rule,

causes it? What are the health risks? What can you do about it? women have more body

What is obesity? fat than men. Most health

care professionals agree “Obesity” specifically refers to an excessive amount of body

fat. “Overweight” refers to an excessive amount of body that men with more than

weight that includes muscle, bone, fat, and water. As a rule, 25 percent body fat and women have more body fat than men. Most health care

women with more than professionals agree that men with more than 25 percent body

fat and women with more than 30 percent body fat are 30 percent body fat are

considered obese. These numbers should not be confused considered obese. These

with the body mass index (BMI), however, which is more numbers should not be commonly used by health care professionals to determine the

effect of body weight on the risk for some diseases. confused with the body

mass index, however,

How is obesity measured? which is more commonly

Measuring the exact amount of a person’s body fat is not used by health care easy. The most accurate measures are to weigh a person

professionals to determine underwater or in a chamber that uses air displacement to

measure body volume, or to use an X-ray test called Dual the effect of body weight

Energy X-ray Absorptiometry, also known as DEXA. These on the risk for some

methods are not practical for the average person, and are diseases. done only in research centers with special equipment.

U.S. DEPARTMENT OF HEALTH

AND HUMAN SERVICES

NATIONAL INSTITUTES OF HEALTH
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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-forheight 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.

Table 1. Body Mass Index
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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 table above 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 appleshaped, 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
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in neighborhoods without sidewalks, tend to

eat out or get “take out” instead of cooking, or

have vending machines with high-calorie, highfat 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 foods 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 moderateintensity 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.
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• 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 http://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-thecounter 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 nonobese men to

develop cancer of the colon, rectum, or

prostate. Women who are considered 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 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.
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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 considered 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 obesityassociated 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 http://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 weightloss drugs. In some cases of extreme obesity,

bariatric surgery may be recommended. (Visit

http://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 are

encouraged to get 60 to 90 minutes of exercise

a day to sustain weight loss.
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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.

Additional Reading From the

Weight-control Information Network

For more information on health risks,

treatment options, and binge eating, refer to

these Weight-control Information Network

(WIN) publications:

Active at Any Size. October 2006.

Available at http://www.win.niddk.nih.gov/

publications/active.htm.

Binge Eating Disorder. June 2008. Available at

http://www.win.niddk.nih.gov/publications/

binge.htm.

Choosing a Safe and Successful Weight-loss

Program. April 2008. Available at

http://www.win.niddk.nih.gov/publications/

choosing.htm.

Do You Know the Health Risks of Being

Overweight? December 2007. Available at

http://www.win.niddk.nih.gov/publications/

health_risks.htm.

Healthy Eating and Physical Activity Across

Your Lifespan: Better Health and You (Tips for

Adults). March 2008. Available in English and

Spanish at http://www.win.niddk.nih.gov/

publications/better_health.htm.

Just Enough for You: About Food Portions.

August 2006. Available at

http://www.win.niddk.nih.gov/publications/

just_enough.htm.

Weight Loss for Life. July 2006. Available at

http://www.win.niddk.nih.gov/publications/

for_life.htm.

For more information on NASH, visit

http://www.digestive.niddk.nih.gov/ddiseases/

pubs/nash/index.htm.
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Additional Reading From Other Organizations

National Institute of Diabetes and Digestive and Kidney

Diseases. Strategic Plan for NIH Obesity Research. U.S.

Department of Health and Human Services (DHHS); National

Institutes of Health (NIH). 2004.

National Heart, Lung, and Blood Institute. Clinical Guidelines

on the Identification, Evaluation, and Treatment of Overweight

and Obesity in Adults. DHHS; NIH. 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:

http://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:

http://www.healthierus.gov/dietaryguidelines. 2005.

This publication is not

copyrighted. WIN encourages

users of this brochure to

duplicate and distribute as

NIH Publication No. 06–3680 many copies as desired.

November 2008

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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, 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, sciencebased 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, Professor,

Department of Exercise Science,

Arnold School of Public Health,

University of South Carolina.

This fact sheet is also available at

http://www.win.niddk.nih.gov.