Obesity 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. Obese children are at higher risk for obesity as adults. People who are overweight or obese are at higher risk for high blood pressure, diabetes, joint pain, and other health problems. In cultures that value being thin, obese people may experience emotional distress and social stigmatization.

What Is Obesity?

Obesity is an abnormal accumulation of body fat or approximately 20 percent or more over an individual’s ideal body weight. The number of people, especially children, who are obese is increasing at an alarming rate in the United States and other parts of the developed world where lifestyles make it easy for people to take in more calories* than their bodies use. People can take in too many calories by eating too many burgers and fries, chips, dips, and nachos, and by drinking too many supersized sweetened soft drinks. They use too few calories by taking car rides instead of walking or riding a bike and by spending too much time seated in front of a television and video games instead of engaging in sports or other physical activities. Over time as the amount of calories from food is greater than the amount of calories used by activity, people gain weight and become overweight or obese. Obesity is a health concern because it is associated with increased risk of illness, disability, and death.

Lifestyle is not the only cause of obesity. Researchers believe that genes* and heredity also play a role in the tendency to gain weight. People with a history of obesity in one or both parents are at higher risk of becoming obese themselves. Studies of adopted children confirm this relationship: The majority of adoptees followed a pattern of weight gain that more closely resembled that of their birth parents than their adoptive parents. Researchers think that people who have inherited “obesity genes” may use calories at a slower rate than others, or they may not have the same appetite shutoff control system that helps lean

 Body Mass Index
Obesity was traditionally defined as a weight at least 20 percent above the weight corresponding to the lowest death rate for individuals of a specifi c height, gender, and age. Th is 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 measuredin 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. Th is calculation produces a number that is the individual’s BMI. An online BMI calculator can be found at http://www.nhlbisupport.com/bmi All adults age 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
Th e BMI of children is calculated in the same way as adults, but instead of assigning a child to a specifi c 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. Children are then assigned a percentile based on their BMI. Th e 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

people stop eating when they have taken in enough calories. Also, people who become obese as children may increase the total number of fat cells in their bodies, making it much more likely that they will be obese as adults. Nevertheless, a genetic predisposition to weight gain does not automatically mean that a person will be obese. Eating habits and pat-terns of physical activity also play a significant role in the amount of weight a person gains. According to the Centers for Disease Control and Prevention (CDC), between the mid-1970s and the early 2000s, the percentage of overweight and obese American adults ages 20 to 74 increased from 15.0 percent to  32.9 percent. During this same time, the percentage of overweight chil-dren two to five years of age increased from 5.0 percent to 13.9 percent  and for children aged 6 to 11 years from 6.5 percent to 18.8 percent.  Overweight and obesity in teens increased from 5.0 percent to 17.4 per-cent. In 2007, the World Health Organization (WHO) estimated that 1.6 billion people worldwide over age 15 were overweight and at least 400
million were obese

What Are the Health Risks Related to Obesity?

Children 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*, and type 2 diabetes*. Often obese children and teens experience social and emotional difficulties because their weight sets them apart from their friends.
Childhood obesity can set the stage for 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  Obese teenagers may have the same problems as obese children, but they also may start having aches and pains as the extra fat in their bodies stresses their joints and overloads their muscles and tendons. Obese teens, as well as some younger children, may show the same health problems commonly seen in obese adults such as high blood pressure and type 2 diabetes. Socially, obesity tends to have an effect on the dating and social lives of teens. Overweight teens also may be at risk for eating disorders*.

Adults For adults, obesity is a serious health risk. Severe obesity is called “morbid” obesity because it is so frequently accompanied by serious health complications. On average, a BMI of greater than 40 (morbidly obese) reduces the lifespan of men by as much as 20 years and of women by 5 years. This is especially true in people who are obese and who also smoke. People who are obese for ten or more years are more likely to die earlier than people who maintain a healthy weight. The quality of life of  an obese person is often diminished by a variety of serious health prob-lems. Some of the risks of adult obesity are listed below.

HEART DISEASE AND STROKE The leading causes of death and disability in the United States are heart disease, heart attack, and stroke. Stroke is a disorder that occurs when a blood vessel to the brain is blocked or bursts. People who are obese are more likely to have high blood pressure (hypertension), which increases the risk of heart disease and stroke. Obesity is also linked to having higher levels of cholesterol and fats (triglycerides) in the blood, which can lead to heart disease.

DIABETES Type 2 diabetes is the most common form of diabetes. Th is 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. Obese people are twice as likely as other people to develop type 2 diabetes. Of particular concern is the fact that type 2 diabetes is occurring with increased frequency among obese children and teens.

CANCER 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 (PROS-tate; 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. For some types of cancer, such as colon and breast, it is not clear whether the greater risk is due to extra body fat or to a high-fat and high-calorie diet.

When Obesity Is Not 

Caused by Overeating

When Obesity Is Not Caused by Overeating Obesity can also be a side effect of certain disorders and conditions, including the following:
■ Cushing’s syndrome, a disorder involving the excessive release of the hormone cortisol
■ Hypothyroidism, a condition caused by an underactive thyroid gland
■ Neurologic disturbances, such as damage to the hypothalamus, a structure located deep within the brain that helps regulate appetite
■ Consumption of such drugs as steroids, antipsychotic medications, or antidepressants
GALLBLADDER DISEASE Obese people are more likely than other people to develop gallbladder disease and gallstones, rock-like 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 Osteoarthritis (os-te-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 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 Sleep apnea (AP-nee-a) is a serious breathing disorder, which 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. Th e more severe the obesity a person has, the greater their 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-size clothing, large-size movie seats and airplane seats, and large-size seat belts in a world designed by and for medium-size people. Depression, anger, frustration, and a feeling that their world is out of control are common among people who are obese.

Many people eat when they feel bored, sad, or angry. In general, though, most obese people are as mentally healthy as anyone else. However, about 30 percent of people who are treated for severe obesity have trouble with binge eating, which means that they eat large amounts of food in a short period while feeling that they cannot control how much they are eating.