Obesity is an abnormal accumulation of body fat, usually 20% or more over an individual's ideal body weight. Obesity is associated with increased risk of illness, disability, and death.
Obesity traditionally has been defined as a weight at least 20% above the weight corresponding to the lowest death rate for individuals of a specific height, gender, and age (ideal weight). Twenty to forty percent over ideal weight is considered mildly obese; 40–100% over ideal weight is considered moderately obese; and 100% over ideal weight is considered severely, or morbidly, obese. More recent guidelines for obesity use a measurment called BMI (body mass index) which is the individual's weight multiplied by 703 and then divided by twice the height in inches. BMI of 25.9–29 is considered overweight; BMI over 30 is considered obese. Measurements and comparisons of waist and hip circumference can also provide some information regarding risk factors associated with weight. The higher the ratio, the greater the chance for weight-associated complications. Calipers can be used to measure skin-fold thickness to determine whether tissue is muscle (lean) or adipose tissue (fat).
Much concern has been generated about the increasing incidence of obesity among Americans. Some studies have noted an increase from 12% to 18% occurring between 1991 and 1998. Other studies have actually estimated that a full 50% of all Americans are overweight. The World Health Organization terms obesity a worldwide epidemic, and the diseases which can occur due to obesity are becoming increasingly prevalent.
Excessive weight can result in many serious, potentially life-threatening health problems, including hypertension, Type II diabetes mellitus (non-insulin dependent diabetes), increased risk for coronary disease, increased unexplained heart attack, hyperlipidemia, infertility, and a higher prevalence of colon, prostate, endometrial, and, possibly, breast cancer. Approximately 300, 000 deaths a year are attributed to obesity, prompting leaders in public health, such as former Surgeon General C. Everett Koop, M.D., to label obesity "the second leading cause of preventable deaths in the United States."
— Rosalyn Carson-DeWitt
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Dictionary: o·be·si·ty (o-be'si-te)
The condition of being obese; increased body weight caused by excessive accumulation of fat.
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Sci-Tech Encyclopedia: Obesity
The presence of excess body fat. The great prevalence of this condition, its severe consequences for physical and mental health, and the difficulty of treating it make the prevention of obesity a major public health priority.
Obesity is most often defined in terms of body weight relative to height, since both height and weight are easily measured. Obesity is considered to begin at a weight-for-height that is 20–30% above desirable weight, with this desirable weight taken as the midpoint of ranges of weight associated with the greatest longevity in studies of life-insured individuals. In population surveys, obesity is defined as a body weight that meets or exceeds the 85th percentile of the Body Mass Index (BMI), an index of weight-for-height that correlates well with body fat content. See also Adipose tissue.
The prevalence of obesity increases with age, is higher in women than men, and is highest among the poor and minority groups. Obesity increases the likelihood of high blood cholesterol, high blood pressure, and diabetes, and therefore of the diseases for which such conditions are risk factors—coronary heart disease, stroke, and kidney disease. It also increases the likelihood of gallbladder disease and cancers of the breast and uterus. Thus, obesity increases overall mortality rates, and it does so in proportion to the degree and duration of overweight. Individuals who become obese at the earliest ages are at highest risk of premature mortality. Distribution of excess fat to the upper body rather than the lower body may also increase risk.
The causes of most cases of obesity are poorly understood. At the simplest level, obesity results from an excess of energy (caloric) intake over expenditure, but this statement does not explain why some individuals can eat as much as they like without gaining weight while others remain overweight despite constant dieting. Studies of genetically obese animals and those with damage to the part of the brain called the hypothalamus suggest that individuals may balance body weight around a "setpoint" that is maintained—without conscious control—by variations in metabolic rate in response to caloric intake. Variations in the prevalence of obesity among population groups suggest a genetic basis for the condition. The complexity of body-weight regulatory mechanisms suggests that obesity is not due to a single cause but, like other chronic diseases, is multifactorial in origin. Specific inherited differences that might influence setpoints include differences in nearly every anatomic, neurologic, and biochemical factor known to affect food intake and utilization, energy metabolism, and energy expenditure. See also Energy metabolism; Metabolic disorders.
Because the causes of obesity are incompletely understood, it is difficult to formulate effective treatment strategies. Studies suggest that programs combining diet and exercise help obese individuals lose more weight and maintain losses longer than either program does separately. See also Food; Nutrition.
Information on prevention and treatment options for obesity.
World of the Body: obesity
Obesity is most commonly defined as a condition of weighing at least 20% over ideal body weight, where ideal body weight is determined in the US by the 1959 or 1983 Metropolitan Life Insurance Company Tables. Like many aspects of obesity, use of life insurance tables as the sole indicator remains controversial. These insurance charts do not take into account the changes in ideal weight with age or provide information on body fat distribution; nor do they base measurements on all ethnic groups and those of the lower socioeconomic classes. To counter such biases, obesity can be determined by body mass index (which relates weight to height) and the percentage of body fat.
The causes of obesity continue to be debated and studied. Though it has long been considered the simple result of too little exercise and too much eating, new research suggests there may also be some hereditary influence, and particularly that the genetic tendency for obesity may be correlated to the mother's weight. Relatively unusual causes include adult-onset diabetes, deficient thyroid hormone secretion, and, very rarely, tumours of the adrenal gland, pancreas, or pituitary gland. Unexplained abnormal function of the brain's appetite control centre may also play a role. Researchers are particularly concerned about the increasing number of children and adolescents who are overweight in the US and Europe.
Obesity may cause a variety of health complications. Most clearly, overweight has an adverse effect on life expectancy. In general, the greater the degree of overweight, the higher the mortality or excess death rate. Obesity may be associated with elevated blood cholesterol, and has been linked to hypertension, diabetes, cancer, coronary artery heart disease, degenerative arthritis, gall stones, sleep disorders, and depression.
For many the 'psychological burden' of being obese in Western cultures, which prize slenderness, particularly in women, is an additional adverse effect. Prior to the nineteenth century, overweight and fatness stood as a sign of health and prosperity, and conveyed social esteem. By the mid and late nineteenth century, a new ethos emerged which championed slenderness as a sign of both beauty and physical health. By the early twentieth century, on the other hand, obesity became associated with laziness, gluttony, and the lower classes. As Keith Walden has written, 'females who stayed slim demonstrated that they had the money and sense to buy nutritious foods and eat balanced meals, and that they had the time to exercise. They did not have menial jobs which required substantial brawn to perform.' In twenty-first-century Western culture, especially for whites, and the middle and upper classes, the abhorrence of fat and obesity continues. As Anne Beller describes it, fat is suicidal: a sin at best and at worst a sort of felony. Yet for many African Americans and Hispanics, as well as other ethnic groups, a larger body still holds positive social value.
Suggested treatments for obesity range from a plethora of rarely successful fad diets to medical procedures such as stapling the stomach to reduce intake or shortening the intestines to curtail absorption. The most tried and true method remains adjustment of the energy balance — decreasing caloric intake while increasing energy usage. Vigorous exercise not only 'burns' nutrient stores but is also shown in some situations to increase metabolic rate for up to 15 hours after activity. Those with a hereditary tendency toward obesity find it more difficult to lose weight, due to a lower resting metabolic rate and possible complications in appetite regulation. In this regard, and in evolutionary terms, a tendency toward obesity can actually have survival value — a lower metabolic rate and a substantial fat store would allow one to live longer in times of famine. But in the contemporary West, where food is relatively plentiful and slenderness highly prized, it works to one's disadvantage.
— Margaret A. Lowe
Beller, A. S. Fat and thin: a natural history of obesity. Farrar, Straus and Giroux, New York.
Walden, K. (1985). The road to Fat City: an interpretation of the development of weight consciousness in Western society. Historical reflections, 12, 331-73
See also body composition; dieting; energy balance; weight.
Food and Nutrition: obesity
Excessive accumulation of body fat. A body mass index above 30 is considered to be obesity (and above 40 gross obesity). The desirable range of BMI for optimum life expectancy is 20-25; between 25 and 30 is considered to be overweight rather than obesity. People more than 50% above desirable weight are twice as likely to die prematurely as those within the desirable weight range.
Food and Fitness: obesity
Obesity is due to the excessive storage of fat in the body, particularly under the skin and around certain internal organs. In 1985, 34 million Americans were obese. Of British adults surveyed in 1991, 13 per cent of men and 15 per cent of women were obese; double the percentage of people who were obese in 1981. A 1995 survey indicates that these figures are continuing to rise. Obesity can be caused by diseases, such as certain cancers, gall-bladder diseases, and hormonal imbalances, but these causes are rare. Many obese people suggest that their condition is due to underactive thyroid glands, but this accounts for less than one in a thousand cases. Most obesity results from eating too much and not exercising enough. This results in a positive energy balance, more energy is consumed than expended. For every 3500 Calories consumed above requirements, approximately one pound of fat is stored in the body.
Obesity is difficult to define quantitatively without knowing how much fat is normal for a given person. Nevertheless, it is generally agreed that the proportion of fat in the body should not exceed 20-25 per cent in men and 28-30 per cent in women. Many medical authorities use body mass as an indicator (see body mass index); people with a body mass index exceeding 30 are considered obese. However, obesity is not the same as being overweight. A very muscular person may be heavy but still have a very low fat content. Heavy body-builders often have less than 10 per cent body fat. There are two main types of obesity: childhood onset obesity and adult onset obesity.
Childhood onset obesity may develop because of hormonal imbalances or some other illness, but it is usually caused by overeating when young. This results in the production of an abnormally high number of adipocytes, cells specialized for fat storage. Adults who were obese as children tend to retain a high number of adipocytes, even if they are thin and have a low fat diet. The high number of adipocytes means that a large storage space is always available for fat. Thus adults who suffered childhood onset obesity are generally predisposed to obesity.
Adult onset obesity occurs when a person becomes obese for the first time after reaching adulthood. He or she usually has a normal number of adipocytes but each one is enlarged with fat. Slimming leads to the fat cells returning to normal size. Adults who have suffered adult onset obesity usually find it much easier to control their weight than adults who were obese as children.
Obesity is a major health hazard. Obese people are predisposed to a number of diseases, including diabetes, high blood pressure, and cardiovascular diseases. Some medical experts suggest that life expectancy decreases by approximately 1 per cent for each pound of excess fat carried by an individual between the ages of 45 and 50.
Dental Dictionary: obesity
A bodily condition marked by excessive generalized deposition and storage of fat.
Alternative Medicine Encyclopedia: Obesity
Obesity is an abnormal accumulation of body fat, usually 20% or more over an individual's ideal body weight. Obesity is associated with increased risk of illness, disability, and death.
The branch of medicine that deals with the study and treatment of obesity is known as bariatrics. As obesity has become a major health problem in the United States, bariatrics has become a separate medical and surgical specialty.
Obesity traditionally has been defined as body weight at least 20% above the weight corresponding to the lowest death rate for individuals of a specific height, sex, and age (designated as the ideal weight). Twenty to forty percent over ideal weight is considered mildly obese; 40–100% over ideal weight is considered moderately obese; and 100% over ideal weight is considered severely, or morbidly, obese. According to some estimates, approximately 25% of the United States population can be considered obese, 4 million of whom are morbidly obese. Other studies state that over 50% of American adults are obese, based on body mass index (BMI) measurements. Excessive weight can result in many serious, and potentially deadly, health problems, including hypertension, Type II diabetes mellitus (non-insulin dependent diabetes), increased risk for coronary disease, increased unexplained heart attack, hyperlipidemia, infertility, and a higher prevalence of colon, prostate, endometrial, and possibly, breast cancer. Approximately 300,000 deaths a year are attributed to obesity, prompting leaders in public health, such as former Surgeon General C. Everett Koop to label obesity "the second leading cause of preventable deaths in the United States."
Causes & Symptoms
The mechanism for excessive weight gain is clear—more calories are consumed than the body burns, and the excess calories are stored as fat (adipose) tissue. However, the exact cause is not as clear and likely arises from a complex combination of factors. Genetic factors significantly influence how the body regulates appetite and the rate at which it turns food into energy (metabolic rate). Studies of adoptees 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. A genetic predisposition to weight gain, however, does not automatically mean that a person will be obese. Eating habits and patterns of physical activity also play a significant role in the amount of weight a person gains.
Some recent studies have indicated that the amount of fat in a person's diet may have a greater impact on weight than the number of calories the food contains. Carbohydrates like cereals, breads, fruits and vegetables, and protein (fish, lean meat, turkey breast, skim milk) are converted to fuel almost as soon as they are consumed. Most fat calories are immediately stored in fat cells, which add to the body's weight and girth as they expand and multiply. There is continuing research on the theory that fat is metabolized as fuel and energy and that only excess carbohydrates are converted to stored fat. Current evidence shows that weight gain comes mostly from total calories consumed, rather than from the amount of carbohydrates. A study published in 2002 found that low-fat diets are no more effective in weight reduction programs than low-calorie diets. At any rate, a sedentary life-style, particularly prevalent in affluent societies like the United States, can contribute to weight gain. Psychological factors, such as depression and low self-esteem may, in some cases, also play a role in weight gain.
At what stage of life a person becomes obese can effect his or her ability to lose weight. In childhood, excess calories are converted into new fat cells (hyperplastic obesity), while excess calories consumed in adulthood only serve to expand existing fat cells (hypertrophic obesity). Since dieting and exercise can only reduce the size of fat cells, not eliminate them, persons who were obese as children can have great difficulty losing weight, since they may have up to five times as many fat cells as someone who became overweight as an adult.
Obesity can also be a side effect of certain disorders and conditions, including:
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 certain drugs, such as steroids, antipsychotic medications, or antidepressants
The major symptoms of obesity are excessive weight gain and the presence of large amounts of fatty tissue. Obesity can also give rise to several secondary conditions, including:
arthritis and other orthopedic problems, such as lower back pain
high cholesterol levels
high blood pressure
menstrual irregularities or cessation of menstruation (amenorhhea)
shortness of breath that can be incapacitating
skin disorders, arising from the bacterial breakdown of sweat and cellular material in thick folds of skin or from increased friction between folds
Dignosis of obesity is made by observation and by comparing the patient's weight to ideal weight charts. Many doctors and obesity researchers refer to the body mass index (BMI), which uses a height-weight relationship to calculate an individual's ideal weight and personal risk of developing obesity-related health problems. Physicians may also obtain direct measurements of an individual's body fat content by using calipers to measure skin-fold thickness at the back of the upper arm and other sites. The most accurate means of measuring body fat content involves immersing a person in water and measuring relative displacement; however, this method is very impractical and is usually only used in scientific studies requiring very specific assessments. Women whose body fat exceeds 30% and men whose body fat exceeds 25% are generally considered obese.
Doctors may also note how a person carries excess weight on his or her body. Studies have shown that this factor may indicate whether or not an individual has a predisposition to develop certain diseases or conditions that may accompany obesity. "Apple-shaped" individuals who store most of their weight around the waist and abdomen are at greater risk for cancer, heart disease, stroke, and diabetes than "pear-shaped" people whose extra pounds settle primarily in their hips and thighs.
Treatment of obesity depends primarily on the degree of a person's overweight and his or her overall health. However, to be successful, any treatment must affect life-long behavioral changes rather than short-term weight loss. "Yo-yo" dieting, in which weight is repeatedly lost and regained, has been shown to increase a person's likelihood of developing fatal health problems than if the weight had been lost gradually or not lost at all. Behavior-focused treatment should concentrate on:
What a person eats and how much. This aspect may involve keeping a food diary and developing a better understanding of the nutritional value and fat content of foods. It may also involve changing grocery shopping habits (e.g. buying only what is on a prepared list and going only on a certain day), timing of meals (to prevent feelings of hunger, a person may plan frequent small meals), and actually slowing down the rate at which a person eats.
How a person responds to food. This may involve understanding what psychological issues underlie a person's eating habits. For example, one person may binge eat when under stress, while another may always use food as a reward. In recognizing these psychological triggers, an individual can develop alternate coping mechanisms that do not focus on food.
How people spend their time. Making activity and exercise an integral part of everyday life is a key to achieving and maintaining weight loss. Starting slowly and building endurance keeps individuals from becoming discouraged. Varying routines and trying new activities also keeps interest high.
For most who are mildly obese, these behavior modifications entail lifestyle changes they can make independently while being supervised by a family physician. Other mildly obese persons may seek the help of a commercial weight loss program (e.g. Weight Watchers). The effectiveness of these programs is difficult to assess, since programs vary widely, dropout rates are high, and few employ members of the medical community. However, programs that emphasize realistic goals, gradual progress, sensible eating, and exercise can be very helpful and are recommended by many doctors. Programs that promise instant weight loss or feature severely restricted diets are not effective and, in some cases, can be dangerous.
For individuals who are moderately obese, medically supervised behavior modification and weight loss are required. While doctors will put most moderately obese patients on a balanced low-calorie diet (1200–1500 calories a day), they may recommend that certain individuals follow a very low-calorie liquid protein diet (400–700 calories) for as long as three months. This therapy, however, should not be confused with commercial liquid-protein diets or commercial weight-loss shakes and drinks. Doctors tailor these diets to specific patients, monitor patients carefully, and use them for only a short period of time. In addition to reducing the amount and type of calories consumed by the patient, doctors will recommend professional therapists or psychiatrists who can help the individual effectively change his or her behavior in regard to eating.
The Chinese herb ephedra (Ephedra sinica, or ma huang), combined with exercise and a low-fat diet in physician-supervised weight-loss programs, can cause at least a temporary increase in weight loss. However, the large doses of ephedra required to achieve the desired result can also cause:
high blood pressure
Ephedra should not be used by anyone with a history of diabetes, heart disease, or thyroid problems. It is not recommended for long-term use, and can cause serious medical or psychiatric problems if used too long. An article that appeared in the Journal of the American Medical Association in early 2003 advised against the use of ephedra.
Diuretic herbs, which increase urine production, can cause short-term weight loss but cannot help patients achieve lasting weight control. The body responds to heightened urine output by increasing thirst to replace lost fluids, and patients who use diuretics for an extended period of time eventually start retaining water again anyway. In moderate doses, psyllium, a mucilaginous herb available in bulk-forming laxatives like Metamucil, absorbs fluid and makes patients feel as if they have eaten enough. Red peppers and mustard help patients lose weight more quickly by accelerating the metabolic rate. They also make people more thirsty, so they crave water instead of food. Walnuts contain serotonin, the brain chemical that tells the body it has eaten enough. Dandelion (Taraxacum officinale) can raise metabolism and counter a desire for sugary foods.
The amino acid 5-hydroxytryptophan, or 5-HTP, which is extracted from the seeds of the Griffonia simplicifolia plant, is thought to increase serotonin levels in the brain. Serotonin is a neurotransmitter, or brain chemical, that regulates mood and thus can be linked to mood-related eating behaviors. When physical and mental stress reduces serotonin levels in the body, 5-HTP may be helpful in regulating mood by boosting serotonin levels. Individuals should consult with their healthcare professional before taking 5-HTP, as the amino acid may interact with other medications and can have potentially serious side effects.
Acupressure and acupuncture can also suppress food cravings. Visualization and meditation can create and reinforce a positive self-image that enhances the patient's determination to lose weight. By improving physical strength, mental concentration, and emotional serenity, yoga can provide the same benefits. Also, patients who play soft, slow music during meals often find that they eat less food but enjoy it more.
Eating the correct ratio of protein, carbohydrates, and good-quality fats can help in weight loss via enhancement of metabolism. Support groups and self-help groups such as Overeaters Anonymous and TOPS (Taking Off Pounds Sensibly) that are informed about healthy, nutritious, and balanced diets can offer an individual the support he or she needs to maintain this type of eating regimen.
For individuals who are severely obese, dietary changes and behavior modification may be accompanied by surgery to reduce or bypass portions of the stomach or small intestine. The risks of obesity surgery have declined in recent years, but it is still only performed on patients for whom other strategies have failed and whose obesity seriously threatens their health. Other surgical procedures are not recommended, including liposuction, a purely cosmetic procedure in which a suction device is used to remove fat from beneath the skin, and jaw wiring, which can damage gums and teeth and cause painful muscle spasms.
A newer approach to weight loss is the development of functional foods, which are food products that incorporate natural compounds shown to help in weight loss programs. These compounds include carbohydrates with a low glycemic index, which help to suppress appetite; green tea extract, which increases the body's energy expenditure; and chromium, which encourages the body to burn stored fat rather than lean muscle tissue. Functional food products are currently undergoing clinical testing.
Appetite suppressant drugs are sometimes prescribed to aid in weight loss. These drugs work by increasing levels of serotonin or catecholamine, which are brain chemicals that control moods and feelings of fullness. Appetite suppressants, though, are not considered truly effective, since most of the weight lost while taking them is usually regained after stopping. Also, suppressants containing amphetamines can be potentially abused by patients. While most of the immediate side effects of these drugs are harmless, the long-term effects in many cases, are unknown. Two 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. In 1999, the United States Food and Drug Administration (FDA) approved a new prescription weight loss drug, Orlistat. Unlike other anti-obesity drugs that act as appetite suppressants, Orlistat encourages weight loss by inhibiting the body's ability to absorb dietary fat. The drug can cause side effects of abdominal cramping, gas, and diarrhea.
Other weight-loss medications available with a doctor's prescription include:
Diethylpropion (Tenuate, Tenuate Dospan)
Mazindol (Mazanor, Sanorex)
Phendimetrazine (Bontril, Prelu-2)
Phentermine (Adipex-P, Fastin, Ionamin, Oby-Cap)
Phenylpropanolamine (Acutrim, Dextarim) is the only nonprescription weight-loss drug approved by the FDA. These over-the-counter diet aids can boost weight loss by 5%. Combined with diet and exercise and used only with a doctor's approval, prescription anti-obesity medications enable some patients to lose 10% more weight than they otherwise would. Most patients regain lost weight after discontinuing use of either prescription medications or nonprescription weight-loss products.
Prescription medications or over-the-counter weight loss products can cause:
None of the weight loss drugs should be used by patients taking monoamine oxidate inhibitors (MAO inhibitors).
Doctors sometimes prescribe fluoxetine (Prozac), an antidepressant that can increase weight loss by about 10%. Weight loss may be temporary and side effects of this medication include diarrhea, fatigue, insomnia, nausea, and thirst. Weight loss drugs currently being developed or tested include ones that can prevent fat absorption or digestion, reduce the desire for food and prompt the body to burn calories more quickly, and regulate the activity of substances that control eating habits and stimulate overeating.
As many as 85% of dieters who do not exercise on a regular basis regain their lost weight within two years. In five years, the figure rises to 90%. Repeatedly losing and regaining weight (yo-yo dieting) encourages the body to store fat and may increase a patient's risk of developing heart disease. The primary factor in achieving and maintaining weight loss is a lifelong commitment to regular exercise and sensible eating habits.
Obesity experts suggest that a key to preventing excess weight gain is monitoring fat consumption rather than counting calories, and the National Cholesterol Education Program maintains that only 30% of calories should be derived from fat. Only one-third of those calories should be contained in saturated fats (the kind of fat found in high concentrations in meat, poultry, and dairy products). Because most people eat more than they think they do, keeping a detailed food diary is a useful way to assess eating habits. Eating three balanced, moderate-portion meals a day—with the main meal at mid-day—is a more effective way to prevent obesity than fasting or crash diets. Exercise increases the metabolic rate by creating muscle, which burns more calories than fat. When regular exercise is combined with regular, healthful meals, calories continue to burn at an accelerated rate for several hours. Finally, encouraging healthful habits in children is a key to preventing childhood obesity and the health problems that follow in adulthood.
New Directions in Obesity Treatment
The rapid rise in the incidence of obesity in the United States since 1990 has prompted researchers to look for new treatments. One approach involves the application of antidiabetes drugs to the treatment of obesity. Metformin (Glucophage), a drug that was approved by the Food and Dug Administration (FDA) in 1994 for the treatment of type 2 diabetes, shows promise in treating obesity associated with insulin resistance.
Another field of obesity research is the study of hormones, particularly leptin, which is produced by fat cells in the body, and ghrelin, which is secreted by cells in the lining of the stomach. Both hormones are known to affect appetite and the body's energy balance. Leptin is also related to reproductive function, while ghrelin stimulates the pituitary gland to release growth hormone. Further studies of these two hormones may lead to the development of new medications to control appetite and food intake.
A third approach to obesity treatment involves research into the social factors that encourage or reinforce weight gain in humans. Researchers are looking at such issues as the advertising and marketing of food products; media stereotypes of obesity; the development of eating disorders in adolescents and adults; and similar questions.