Obesity (o-BEE-si-tee) is a significant excess of body fat to the point where the ratio of body fat to total body mass is higher than accepted norms. This condition can result from a variety of causes, some of which are genetic and some of which are related to lifestyle choices. Obesity affects millions of adults and children worldwide and can negatively impact quality of life and lead to serious health problems. In cultures that value being thin, obese people may also experience emotional distress and social stigmatization.

Karen's Story

Karen was a normal, healthy baby who grew into a very chubby child. By the time she was 12 years old, Karen was 50 pounds overweight. Because she was so heavy, she did not enjoy sports or other physical activities, so she spent much of her free time snacking in front of the television or chatting online with friends. As Karen gained weight, it became more difficult for her to catch her breath when she was active. She hated gym class and found it hard to deal with the teasing of classmates. Finally, after talking to the mother of a friend who had lost weight, Karen decided she needed to make changes to lose weight. Because both of her parents were also overweight, Karen enlisted them to make weight loss a family project. Karen and her parents began going to the local YMCA to exercise. They also slowly changed their eating habits and stopped buying so much snack food. Soon, they were eating a leaner, healthier diet. Even though it sometimes seemed difficult and took longer than she had hoped, Karen lost weight and began to enjoy a more active lifestyle.

What Is Obesity?

Obesity is accumulation of body fat that totals 20 percent or more over an individual's ideal body weight. In the United States, and other parts of the developed world, lifestyles make it easy for people to consume more calories *

Obesity was traditionally defined as a weight at least 20 percent above the weight corresponding to the lowest death rate for individuals of a specific height, gender, and age. This weight was designated the ideal weight. Current guidelines for obesity use a measurement called the body mass index (BMI). BMI is a mathematical formula that uses height and weight to compare the ratio of body fat to total body mass. To calculate the BMI in metric units (weight measured in kilograms and height measured in meters): BMI = kg/m2. To calculate BMI in English units, weight in pounds (lb) is divided by height squared in inches (in) and then multiplied by 703. This calculation produces a number that is the individual's BMI. An online BMI calculator can be found at http://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm .

All adults ages 20 and older are evaluated on the same BMI scale as follows:

  • BMI below 18.5: underweight
  • BMI 18.5–24.9: normal weight
  • BMI 25.0–29.9: overweight
  • BMI 30 and above: obese

The BMI of children is calculated in the same way as adults, but instead of assigning a child to a specific weight category based on his or her BMI, a child's BMI is compared to that of other children of the same age and sex. This difference in procedure is because of the expected bodily changes that occur as children and teens grow. After the child's BMI has been calculated, the child is assigned a percentile based on that BMI. The percentile tells them how their weight compares to that of other children who are their age and gender, as follows:

  • Below the 5th percentile: underweight
  • 5th percentile to less than the 85th percentile: healthy weight
  • 85th percentile to less than the 95th percentile: at risk of overweight
  • 95th percentile and above: overweight

Lifestyle is not the only cause of obesity. Researchers believe that genes *

According to the Centers for Disease Control and Prevention (CDC), the number of obese adults and youths increased significantly between 1999 and 2014. The organization stated in a November 2015 report that more than one-third (approximately 36.5 percent) of adults in the United States were considered obese between 2011 and 2014. During those years, obesity was found to be higher in middle-aged adults (40 to 59 years old) and older adults (60 years and up) than among younger adults. Among adults, obesity was more prevalent in women than men. Childhood obesity in the United States remained fairly stable from 2005 to 2014 at 17 percent (12.7 million children and adolescents). Obesity among young children aged two to five years old decreased from around 14 percent in 2004 to approximately 8 percent in 2012. This drop is considered particularly significant since children in that age group who are obese are considered five times more likely to also be obese as adults. Among children, there was no significant difference in obesity rates between males and females, except among non-Hispanic Asians.

In 2014, the World Health Organization (WHO) estimated that 1.9 billion adults over age 18 worldwide were overweight and at least 600 million of those were obese. Forty-two million children under the age of five were obese or overweight in 2013.

What Are the Health Risks Related to Obesity?


Children who are in the 85th percentile or above are at risk for developing health problems related to obesity beginning in childhood. Children may have fewer visible health problems from being heavy than adults do. However, the more overweight the child is, the more likely he or she will develop high blood pressure, high levels of cholesterol * , type 2 diabetes * , breathing problems, and liver damage. Often obese children and teens experience social and emotional difficulties because their weight sets them apart from their peers.

Childhood obesity can lead to a lifetime of weight control struggles. In childhood, excess calories are converted into new fat cells, while excess calories consumed in adulthood only expand existing fat cells. Because dieting and exercise can only reduce the size of fat cells, not eliminate them, people who are obese as children can have great difficulty losing weight as adults because they may have up to five times more fat cells than someone who first becomes overweight as an adult.

Teens * .


For adults, obesity is a serious health risk. The highest level of obesity, Class III obesity, occurs when a person has a BMI greater than 40. A 2014 National Institutes of Health (NIH) study found evidence that people in this class could have their life expectancies shortened between 6.5 years for those with BMIs between 40-44.9 to 13.7 years for those with BMIs between 55-59.9. Health risks are increased for obese persons who also smoke. The quality of life of an obese person is often diminished by a variety of serious health problems. Some of the risks of adult obesity are:


As of 2015, the leading cause of death in the United States was heart disease (with cancer as a close second). People who are obese are more likely to have high blood pressure (hypertension), which increases the risk of heart disease. Obesity is also linked to having higher levels of cholesterol and fats (triglycerides) in the blood, which can lead to heart disease.


Type 2 diabetes is the most common form of diabetes. This disorder reduces the body's ability to use insulin to control blood sugar levels. It is a major cause of early death, heart disease, kidney disease, stroke, and blindness. Eighty to ninety percent of persons with type 2 diabetes are overweight or obese. Obesity places extra stress on the body, which makes it more difficult for the body to maintain proper blood sugar levels. Of particular concern is the fact that type 2 diabetes is occurring with increased frequency among obese children and teens.


Men who are obese are more likely than other men to get cancer of the colon (main part of the large intestine), rectum (lower part of the large intestine), and prostate (PRAH-state; male gland in front of the rectum). Obese women are more likely than other women to get cancer of the colon, uterus, cervix (lower part of the uterus), ovaries (female glands where egg cells develop), gallbladder (small sac under the liver), and breast.


Obese people are more likely than other people to develop gallbladder disease and gallstones, rocklike lumps that form in the gallbladder. Ironically, rapid weight loss itself can also lead to gallstones. Slower weight loss of about one pound a week is less likely to cause this problem.


Osteoarthritis (ah-stee-o-ar-THRY-tis) is a common disease that affects the joints (places where bones meet), especially those in the knees, hips, and lower back. Extra weight seems to promote osteoarthritis by putting extra pressure on these joints and wearing away the tissue that cushions and protects them.


Gout (GOWT) is a joint disease that can lead to problems with the kidneys (organs that filter blood and get rid of waste products and excess water as urine). Gout is more common in people with obesity. Some diets may cause an attack of gout in people who are prone to it. Such people should visit a doctor and ask if they need to be on a special diet.


Sleep apnea (AP-nee-uh) is a serious breathing disorder that can cause a person to stop breathing for short periods during sleep and to snore heavily. It can lead to daytime sleepiness and, sometimes, heart failure. The more obese a person is, the greater the risk of getting sleep apnea.

Social and psychological conditions

People who are obese may face discrimination when they apply for jobs or promotions, and studies have shown that they may be unfairly viewed by others as lazy or less intelligent. Obese adults often experience the inconvenience and frustration of needing large-sized clothing, large-sized movie seats and airplane seats, and large-sized seat belts in a world designed by and for medium-sized people. Depression, anger, and frustration are common among people who are obese.

Many people eat when they feel bored, sad, or angry. Depression is also frequently a factor in obesity, and vice versa. Women are more likely than men to suffer from this combination, which can lead to suicidal thoughts in some individuals. Many people with binge eating disorder (BED) are obese, although most obese people do not have BED. BED is characterized by recurring episodes of eating large amounts of food in short periods of time and feelings of shame, guilt, and a loss of control due to these episodes.

How Is Obesity Treated?

Research shows that the best way for people of all ages to control their weight is through regular exercise and a portion-controlled, balanced diet. Adults can improve their health by losing as little as 5 percent of their body weight. To lose weight, people must take in fewer calories than they use. They can do this by becoming more active and/or eating less. The best weight-loss programs combine both of these approaches and also teach people healthy habits that they can follow for the rest of their lives.


Studies show that regular physical activity, combined with a good diet, is the healthiest and most effective way to control weight. Exercise uses excess calories that would otherwise be stored as fat.

Percentage of high school students who were physically active during the past week,* by sex, race/ethnicity, and grade, 2013

Percentage of high school students who were physically active during the past week,* by sex, race/ethnicity, and grade, 2013
SOURCE: Centers for Disease Control and Prevention (CDC). Youth Risk Behavior Surveillance-United States, 2013. MMWR 2014; 63(No. SS-4): 147. Table by Lumina Datamatics Ltd. © 2016 Cengage Learning®.
Fad Diets

Fad diets are diets that claim to help people lose a lot of weight in a short time, often without making lifestyle changes. They become fads when they are widely advertised and reported in magazines, newspapers, television, and radio.

Fad diets often require eating a particular food or food group. Examples of fad diets include the raw food diet, cabbage soup diet, the grapefruit diet, and the master cleanse. These diets are not nutritionally balanced and can lead to serious health problems.

For healthy and sustained weight reduction, the CDC recommends losing no more than one to two pounds per week. The best diets for achieving this recommend exercising and eating controlled amounts of a balance of foods from all food groups. It is important to talk with a doctor before trying any diet.

Muscle-strengthening exercises, such as weight training, and stretching exercises should also be part of a balanced exercise program. In addition to burning calories, these activities strengthen the muscles and bones and help prevent injury. Such exercises should be done at least twice a week. Children should participate in sixty minutes of physical activity per day, although this doesn't have to occur all at once. Parents should encourage their children to become involved in sports or noncompetitive movement-related activities and schedule time for the entire family to be active together.


Children should never go on a diet to lose weight unless a doctor tells them to do so for medical reasons. Limiting what children eat can interfere with their growth and may be harmful to their health. Instead, children should shift to eating better foods, with most coming from the grain, vegetable, and fruit groups. Some foods from the milk, meat, and bean groups should also be included. Junk foods, which provide few vitamins and minerals but are full of fat and sugar, should be eaten sparingly or avoided altogether. Fat should not be restricted in the diet of children under two years of age. For children between the ages of four and eighteen, 25 to 35 percent of their calories should come from fat. Simple ways to cut back on fat include eating low-fat or nonfat dairy products, lean meats, and other low-fat or fat-free foods.

Adults who are trying to lose weight often go on low-calorie diets. Such diets typically contain 1,000 to 1,500 calories per day. The exact number of calories that is right depends on a person's size and activity level. The goal should be to lose no more than two pounds a week while still eating a varied diet that includes plenty of grains, vegetables, fruits, and other healthful foods.

A doctor may prescribe a medically supervised, very low-calorie diet for severely obese individuals. These specially formulated diets contain no more than 800 calories a day. Such diets can lead to faster weight loss than ordinary low-calorie diets. Because serious side effects such as gallstones can develop, very low-calorie diets should always be supervised by a physician and/or nutritionist.

Some researchers have found that low- and very low-calorie diets do not support long-term weight loss. These studies show that as soon as calorie intake is reduced, the body conserves energy, meaning the number of calories expended falls. Reduced calorie intake reduces muscle as well as fat. Other recommendations include increasing exercise and calorie intake to build more muscle while reducing fat.

Weight-Loss Supplements

The weight-loss supplement industry is a big business. Dietary supplements that claim to suppress appetite, burn more calories, and produce dramatic weight loss are sold without a prescription and are not subject to the same rigorous testing for safety and effectiveness as over-the-counter or prescription drugs.

Many heavily promoted weight-loss products are based on fads or gimmicks that create false hopes but rarely produce long-term weight loss. Some of these products, even ones promoted as natural or herbal, can actually endanger health, especially in people who have other chronic illness (e.g., diabetes, heart disease). Individuals should consult a physician before taking any weight-loss product.


Appetite-suppressant drugs are sometimes prescribed to aid in weight loss. These drugs work by increasing levels of brain chemicals that control feelings of fullness. Appetite suppressants, though, are rarely truly effective because most of the weight lost while taking them is regained after stopping them. Also, suppressants containing amphetamines can be potentially abused by patients. These drugs may have potentially harmful side effects. Two appetite-suppressant drugs, dexfenfluramine hydrochloride (Redux) and fenfluramine (Pondimin), as well as a combination fenfluramine-phentermine (Fen/Phen) drug, were taken off the market when they were shown to cause potentially fatal heart defects.

Until 2012 only one drug, orlistat (sold as Alli over the counter and as Xenical with a prescription), was approved by the Food and Drug Administration (FDA) for long-term use. In 2012, however, the FDA green-lit two new drugs, lorcaserin (Belviq) and an aphentermine/topiramate combination (Qsymia). Then in 2014 it approved a buproprion/naltrexone combination (Contrave) and an injectible drug, liraglutide (Saxenda). All of these newer drugs require a doctor's prescription, and all have significant side effects that should be taken into consideration. Some doctors have found that antidepressant medications * help obese people gain control over their eating habits but an unfortunate side effect of some types of antidepressants is weight gain, so caution must be exercised.


Surgical procedures reduce the size of the stomach through stapling or banding so that the person feels full quickly. The exit to the stomach may also be relocated to bypass part of the small intestine so that fewer calories are absorbed into the blood. Weight-loss surgery has some major risks and side effects. It is only performed after extensive medical tests and psychological, behavioral, and nutritional counseling on people for whom the benefits outweigh the risks. The cost of this surgery is often covered by insurance.

Height and weight goals

Height and weight goals
SOURCE: Doctors On-Line, Inc. “Height and Weight Goals as Determined by the Metropolitan Life Insurance Company.” Table by PreMediaGlobal. © 2016 Cengage Learning®.

Controlling Weight

Weight control is not easy and requires a long-term effort. It does not help much for a person to lose lots of weight only to regain it. Keeping weight off is the toughest part of a weight-loss program for most people. The key to keeping pounds off or stopping obesity before it starts is to learn healthy habits that last a lifetime. Here are some hints:

See also Anorexia Nervosa • Arthritis • Body Image • Bulimia Nervosa and Binge Eating Disorder • Cancer: Overview • Diabetes • Eating Disorders: Overview • Gallbladder Disease • Gout • Heart Disease: Overview • Sleep Disorders: Overview • Thyroid Disease

When Obesity Is Not Caused by Overeating

Obesity can also be a side effect of certain disorders and conditions, including the following:


Books and Articles

Akabas, Sharon, Sally Ann Lederman, and Barbara J. Moore. Textbook of Obesity: Biological, Psychological, and Cultural Influences. Hoboken, NJ: Wiley-Blackwell, 2012.

Cohen, Deborah. A Big Fat Crisis: The Hidden Forces Behind the Obesity Epidemic—And How We Can End It. New York, NY: Nation Books, 2013.

Eden, Alvin N., Barbara J. Moore, and Adrienne Forman. Fit from the Start: How to Prevent Childhood Obesity in Infancy. Clyde Park, MT: Shape Up America! 2014.

https://www.washingtonpost.com/news/wonk/wp/2015/07/28/why-the-most-popular-rule-of-weight-loss-is-completely-wrong/ (accessed March 3, 2016).

Kolata, Gina. “Obesity Is Found to Gain Its Hold in Earliest Years.” The New York Times. January 29, 2014. http://www.nytimes.com/2014/01/30/science/obesity-takes-hold-early-in-life-study-finds.html (accessed March 3, 2016).

Taubes, Gary. Why We Get Fat and What We Can Do About It. New York: Anchor, 2011.


Centers for Disease Control and Prevention. “Overweight & Obesity.” http://www.cdc.gov/obesity/ (accessed March 3, 2016).

MedlinePlus. “Obesity.” U.S. National Library of Medicine, National Institutes of Health. https://www.nlm.nih.gov/medlineplus/obesity.html (accessed March 3, 2016).

Merck Manual: Consumer Version. “Obesity.” http://www.merckmanuals.com/professional/nutritional-disorders/obesity-and-the-metabolic-syndrome/obesity (accessed March 3, 2016).

National Institute of Diabetes and Digestive and Kidney Diseases. “Weight-Control Information Network.” National Institues of Health. (accessed March 3, 2016).

World Health Organization. “Obesity.” http://www.who.int/topics/obesity/en/ (accessed March 3, 2016).


Academy of Nutrition and Dietetics. 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606. Toll-free: 800-877-1600. Website: http://www.eatright.org (accessed March 3, 2016).

Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30329. Toll-free: 800-232-4636. Website: http://www.cdc.gov (accessed March 3, 2016).

National Institute of Diabetes and Digestive and Kidney Diseases. Bethesda, MD 20892. Telephone: 301-496-3583. Website: http://niddk.nih.gov (accessed March 3, 2016).

National Institutes of Health. 9000 Rockville Pike, Bethesda, MD 20892. Telephone: 301-496-4000. Website: http://www.nih.gov/ (accessed March 3, 2016).

National Obesity Foundation. 10921 Wilshire Blvd., #1114, Los Angeles, CA 90024. Toll-free: 800-663-9300. Website: http://nofusa.org (accessed March 3, 2016).

Obesity Action Coalition. 4511 North Himes Ave., Suite 250, Tampa, FL 33614. Toll-free: 800-717-3117. Website: http://www.obesityaction.org (accessed March 3, 2016).

The Obesity Society. 8757 Georgia Ave., Suite 1320, Silver Spring, MD 20910. Telephone: 301-563-6526. Website: http://www.obesity.org (accessed March 3, 2016).

Shape Up America! PO Box 140, Clyde Park, MT 59018. Telephone: 406-686-4424. Website: http://www.shapeup.org (accessed March 3, 2016).

World Health Organization. Avenue Appia 20, 1211 Geneva 27, Switzerland. Telephone: 41-22-791-21-11. Website: http://www.who.int (accessed March 3, 2016).

* calories (KAL-or-eez) are units of energy that are used to describe both the amount of energy in food and the amount of energy the body uses.

* genes (JEENS) are chemical structures composed of deoxyribonucleic acid (DNA) that help determine a person's body structure and physical characteristics such as hair or eye color. Inherited from a person's parents, genes are contained in the chromosomes found in the body's cells.

* cholesterol (ko-LES-ter-ol) is a fatlike substance found in the blood and body tissues.

* diabetes (dye-uh-BEE-teez) is a condition in which the body's pancreas does not produce enough insulin or the body cannot use the insulin it makes effectively, resulting in increased levels of sugar in the blood. This can lead to increased urination, dehydration, weight loss, weakness, and a number of other symptoms and complications related to chemical imbalances within the body.

* eating disorders are conditions in which a person's eating behaviors and food habits are so unbalanced that they cause physical and emotional problems.

* antidepressant medications are used for the treatment and prevention of depression.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)