Understanding

Adult Obesity

WIN Weight-control Information Network

“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,

however, which is more

commonly used by health

care professionals to

determine the effect of

body weight on the risk 

for some diseases.

Today, more than 65 percent of adults 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 above 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. 

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

2

Weight in Pounds**

BMI (Body Mass Index)

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 Adults: 

The Evidence Report.
3

around their bellies, giving them more of an

“apple” shape. Of course, some men are pearshaped 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 highcalorie 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 highincome 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 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. 

■ 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 fluidfilled 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-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 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 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 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

4
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

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 adulthood. Previously

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

healthcare professional before starting a moderateintensity 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 Weightcontrol 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 Adults).

Available in English and Spanish. Available from

WIN and online at

5
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

National Institutes of Health

NIH Publication No. 01-3680

October 2001

Updated March 2006

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 national 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, 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.

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

Adults. 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.