• How is Obesity Measured?
  
• Weight-for-Height Tables
  
• Body Mass Index (BMI)
  
• Body Fat Distribution: "Pears" vs. "Apples"
  
• Waist-to-Hip Ratio
  
• What Causes Obesity?
  
• What Are the Consequences of Obesity?
  
• Who Should Lose Weight?
  
• How is Obesity Treated?
  
• Research on Obesity
  
• Additional Reading on Obesity
  

This fact sheet provides basic information about obesity: what it is, what causes it, how to measure it. Companion fact sheets provide more in-depth information about some aspects addressed briefly here, such as health risks of obesity and treatment options for the condition.

There are two simpler methods for estimating body fat, but they can yield inaccurate results if done by an inexperienced person or if done on someone with severe obesity. One is to measure skinfold thickness in several parts of the body. The second involves sending a harmless amount of electric current through a person's body (bioelectric impedance analysis). Both methods are commonly used in health clubs and in commercial weight-loss programs, but results should be viewed skeptically.

Because measuring a person's body fat is tricky, doctors often rely on other means to diagnose obesity. Two widely used measurements are weight-for-height tables and body mass index. While both measurements have their limitations, they are reliable indicators that someone may have a weight problem. They are easy to calculate and require no special equipment.

One problem with using weight-for-height tables is that doctors disagree over which is the best table to use. Many versions are available, all with different weight ranges. Some tables take a person's frame size, age, and sex into account; others do not. A limitation of all weight-for-height tables is that they do not distinguish excess fat from muscle. A very muscular person may appear obese, according to the tables, when he or she is not. Still, weight-for-height tables can be used as general guidelines.

The table printed here is from the 1990 edition of Dietary Guidelines for Americans, a pamphlet printed jointly by the U.S. Departments of Agriculture and Health and Human Services. This table has a wide range for what the pamphlet calls "healthy" or "suggested" weights.

In this table, the higher weights generally apply to men, who tend to have more muscle and bone. The lower weights more often apply to women, who have less muscle and bone. The table also shows higher weights for people age 35 and older, which some experts question.

In general, a person age 35 or older is obese if he or she has a BMI of 27 or more. For people age 34 or younger, a BMI of 25 or more indicates obesity. A BMI of more than 30 usually is considered a sign of moderate to severe obesity.

The BMI measurement poses some of the same problems as the weight-for-height tables. Doctors don't agree on the cutoff points for "healthy" versus "unhealthy" BMI ranges. BMI also does not provide information on a person's percentage of body fat. However, like the weight-for-height table, BMI is a useful general guideline.

Women typically collect fat in their hips and buttocks, giving their figures a "pear" shape. Men, on the other hand, usually build up fat around their bellies, giving them more of an "apple" shape. This is not a hard and fast rule, though. Some men are pear-shaped and some women become apple-shaped, especially after menopause.

People whose fat is concentrated mostly in the abdomen are more likely to develop many of the health problems associated with obesity.

Doctors have developed a simple way to measure whether someone is an apple or a pear. The measurement is called waist-to-hip ratio.

35 ÷ 46 = 0.76

Women with waist-to-hip ratios of more than 0.8 or men with waist-to-hip ratios of more than 1.0 are "apples." They are at increased health risk because of their fat distribution.

Genetic Factors

Obesity tends to run in families, suggesting that it may have a genetic cause. However, family members share not only genes but also diet and lifestyle habits that may contribute to obesity. Separating these lifestyle factors from genetic ones is often difficult. Still, growing evidence points to heredity as a strong determining factor of obesity. In one study of adults who were adopted as children, researchers found that the subjects' adult weights were closer to their biological parents' weights than their adoptive parents'. The environment provided by the adoptive family apparently had less influence on the development of obesity than the person's genetic makeup.

Nevertheless, people who feel that their genes have doomed them to a lifetime of obesity should take heart. As discussed in the next section, many people genetically predisposed to obesity do not become obese or manage to lose weight and keep it off.

Environmental Factors

Although genes are an important factor in many cases of obesity, a person's environment also plays a significant part. Environment includes lifestyle behaviors such as what a person eats and how active he or she is. Americans tend to have high-fat diets, often putting taste and convenience ahead of nutritional content when choosing meals. Most Americans also don't get enough exercise.

People can't change their genetic makeup, of course, but they can change what they eat and how active they are. Some people have been able to lose weight and keep it off by:

• Learning how to choose more nutritious meals that are lower in fat.
• Learning to recognize environmental cues (such as enticing smells) that may make them want to eat when they are not hungry.
• Becoming more physically active.

Psychological factors also may influence eating habits. Many people eat in response to negative emotions such as boredom, sadness, or anger.

While most overweight people have no more psychological disturbance than normalweight people, about 30 percent of the people who seek treatment for serious weight problems have difficulties with binge eating. During a binge eating episode, people eat large amounts of food while feeling they can't control how much they are eating. Those with the most severe binge eating problems are considered to have binge eating disorder. These people may have more difficulty losing weight and keeping the weight off than people without binge eating problems. Some will need special help, such as counseling or medication, to control their binge eating before they can successfully manage their weight.

Other Causes of Obesity

Some rare illnesses can cause obesity. These include hypothyroidism, Cushing's syndrome, depression, and certain neurologic problems that can lead to overeating. Certain drugs, such as steroids and some antidepressants, may cause excessive weight gain. A doctor can determine if a patient has any of these conditions, which are believed to be responsible for only about 1 percent of all cases of obesity.

Obesity is not just a cosmetic problem. It's a health hazard. Someone who is 40 percent overweight is twice as likely to die prematurely as an average-weight person. (This effect is seen after 10 to 30 years of being obese.)

Obesity has been linked to several serious medical conditions, including diabetes, heart disease, high blood pressure, and stroke. It is also associated with higher rates of certain types of cancer. Obese men are more likely than nonobese men to die from cancer of the colon, rectum, and prostate. Obese women are more likely than nonobese women to die from cancer of the gallbladder, breast, uterus, cervix, and ovaries.

Other diseases and health problems linked to obesity include:

• Gallbladder disease and gallstones.
• Osteoarthritis, a disease in which the joints deteriorate, possibly as a 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.

Psychological and Social Effects

One of the most painful aspects of obesity may be the emotional suffering it causes. American society places great emphasis on physical appearance, often equating attractiveness with slimness, especially in women. The messages, intended or not, make overweight people feel unattractive. Many people assume that obese people are gluttonous, lazy, or both. However, more and more evidence contradicts this assumption. Obese people often face prejudice or discrimination at work, at school, while looking for a job, and in social situations. Feelings of rejection, shame, or depression are common.

Many obesity experts believe that people who are less than 20 percent above their healthy weight should try to lose weight if they have any of the following risk factors.

Risk Factors

• Family history of certain chronic diseases. People with close relatives who have had heart disease or diabetes are more likely to develop these problems if they 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. People whose weight is concentrated around their abdomens may be at greater risk of heart disease, diabetes, or cancer than people of the same weight who are pear-shaped.

Fortunately, even a modest weight loss of10 to 20 pounds can bring significant health improvements, such as lowering one's blood pressure and cholesterol levels.

NIDDK also oversees the National Task Force on Prevention and Treatment of Obesity. The task force comprises leading obesity and nutrition experts who gather and assess the latest information on obesity treatment and prevention. The task force also helps guide basic and clinical research on obesity. Scientific papers and general-interest brochures and pamphlets approved by the task force are available from the NIDDK's Obesity Resource Information Center.

In addition to NIDDK, other sections of the NIH sponsor obesity research. They include:

• The National Heart, Lung, and Blood Institute (NHLBI)
• The National Center for Research Resources (NCRR)
• The National Institute of Child Health and Human Development (NICHD)
• The National Institute on Mental Health (NIMH)
• The National Cancer Institute (NCI)
• The National Institute on Aging (NIA)
• The National Institute of Nursing Research (NINR)
• The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
• The National Institute of Neurological Diseases and Stroke (NINDS)
• The National Institute of Environmental and Health Sciences (NIEHS).

Bray, G.A. "Pathophysiology of Obesity." American Journal of Clinical Nutrition. 1992; Supplement to Vol. 55 (2): 488S-494S. This article comes from the proceedings of an NIH Consensus Development Conference on Gastrointestinal Surgery for Severe Obesity. Written for health professionals in technical language. Available in medical libraries.

"Dietary Guidelines for Americans." Third Edition, 1990. Home and Garden Bulletin No. 232. This pamphlet, issued by the U.S. Agriculture and Health and Human Services Departments, contains information about maintaining a healthy weight, as well as dietary and nutrition recommendations. Available through the Government Printing Office, Publication No. 1990-273-930.

"Exercise and Weight Control." The President's Council on Physical Fitness and Sports, Department of Health and Human Services. This brochure discusses the difference between being "overweight" and "overfat" and the role diet and exercise can play in a weight loss program. Copies can be obtained from the President's Council on Physical Fitness and Sports, Dept. No. 176, 701 Pennsylvania Ave. NW, Washington, DC 20004.

"The Facts About Weight Loss Products and Programs." This brochure, produced by the Federal Trade Commission in conjunction with the Food and Drug Administrat.gov

The Weight-control Information Network (WIN) is a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health, under the U.S. Public Health Service. Authorized by Congress (Public Law 103-43), WIN assembles and disseminates to health professionals and the public information on weight control, obesity, and nutritional disorders. WIN responds to requests for information; develops, reviews, and distributes publications; and develops communications strategies to encourage individuals to achieve and maintain a healthy weight.

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e-text last updated: 9 February 1998