OBESITY

Definition

Obesity is a condition of excessive fatness. Fatness is often expressed as a percentage of body weight. Prepubertal boys and girls typically have about 15 percent of their body weight as fat, while the average adult male is 20 percent fat, and the average adult female is 30 percent fat. Body fatness is measured using a variety of techniques, such as body densitometry, electrical impedance, and skin-fold thickness. Total body weight, although it includes muscle, bone, and internal organs, in addition to body fat, can be used as an index of fatness, especially when expressed in relation to body height. A ratio of weight and height, called the body mass index (BMI), has been adopted for use in the assessment of children, adolescents, and adults. BMI is calculated by dividing the weight, in kilograms, by the square of the height, in meters (kg/m2). If pounds and inches are used, then the quotient (pounds divided by inches squared) multiplied by 704.5. For adult men and women, BMI greater than 25 signifies overweight, and BMI greater than 30 indicates obesity. During childhood, BMI varies by gender and normally increases with age. Obesity is determined with a graph or reference table that gives the eighty-fifth percentile for age (as a criteria for overweight) and the ninety-fifth percentile for age (as a criteria for obese) for boys and girls. In 2000 the CDC published revised percentile standards for BMI (see Table).

Causes

Obesity is caused by a variety of factors, all of which result in an excess of caloric intake relative to the body's expenditure of energy (calories) at rest, during activity, and, in childhood and adolescence, for growth. Calorie intake in excess of these needs is converted to fat. Less than 2 percent of obesity in childhood is due to endocrinologic conditions, such as thyroid disease. An equally small percentage is due to genetic disorders (e.g., the Prader-Willi Syndrome). Though obesity "runs in families," the genetic contributions to fatness are not well understood. A shared environment also contributes to the hereditary pattern of obesity, with parental influences on diet and exercise during childhood and adolescence. Numerous studies have failed to precisely define the relative contributions of caloric intake and expenditure to the development of obesity. The difference in daily intake necessary to result in as much as a ten-pound difference in weight gain over the course of a year is actually as little as a hundred calories per day. Studies have shown that more time spent using television, VCRs, and video games is associated with a greater likelihood of obesity and that decreasing the amount of time spent watching television correlates with less weight gain.

Some interesting developmental factors may contribute to overconsumption of calories. These include difficult infant or child temperament, poor self-regulation of intake, and an "obese eating style," involving rapid eating and rapid consumption of calories. Studies of infant feeding have revealed a style of vigorous feeding, similar to the obese eating style, with rapid sucking, at higher pressure, resulting in greater caloric intake at a feed. Studies of children's ability to self-regulate dietary intake have found poorer self-regulation of eating in fatter girls and in children exposed to a highly controlling parenting style. Studies of child temperament have found that difficult children (low in rhythmicity, approach, and adaptability; high in intensity; and negative in mood) show more rapid weight gain, perhaps as a result of being overfed by parents who use feeding as a soothing technique, and may later use eating as a technique for comforting themselves.

Consequences

Obesity has significant medical consequences, especially for adults, but also for children and adolescents. Among adults, obesity is a major risk factor for heart disease, myocardial infarction (heart attack), strokes, cancer, and many other diseases. During adolescence and childhood, obesity can contribute to problems of the joints, especially the hips, knees, and spine, and more difficulty with chronic illnesses, such as asthma. Obesity affects the endocrine system, leading to changes in sex hormones, adrenal hormones, and the ability to respond appropriately to insulin. Type II diabetes has become more common during adolescence as the prevalence of obesity has increased. Sleep apnea, due to obstructed breathing during sleep, is more common among obese children and adolescents.

The psychological consequences of obesity are very important during childhood and adolescence. Though some studies have found similar prevalence of psychological problems in obese and normal weight children, obese children are often teased by other children, excluded from peer group activities, picked last (if at all) for sports teams, and shunned during social activities. Stigmatization of obesity is commonplace throughout the media, especially television, movies, and popular magazines. Unfortunately, poor self-esteem, depression, and the development of eating disorders occur often in individuals with histories of obesity. Obese adults are even discriminated against when they apply for jobs and during the application process for college.

Treatment

Obesity is not a disease that can be diagnosed on the basis of one or more blood tests or treated with one or a combination of medications. Until the true genetic contributions to the development of excessive fatness are better understood, treatment will remain a process of managing the balance between calorie in-take and expenditure. This behavioral treatment process must support reduction in calorie intake, modification of food selection, reduction in sedentary time, and increase in caloric expenditure. Important components of change include the use of diet diaries, to help recognize needed diet change, and the careful replacement of unhealthy food choices with lower calorie items that supply adequate amounts of protein, carbohydrates, minerals, and vitamins. Similarly, increasing energy expenditure can be the result of reducing reliance on cars, public transportation, elevators, and other conveniences, while increasing the time spent walking, bicycling, or other ways of expending energy, such as using stairs.

Modification of diet and activity and change in the degree of obesity among children over the age of eight years can occur in weekly group treatment programs that also involve parents in separate group sessions. Three treatment program characteristics contribute most to positive results: comprehensive treatment (including a combination of behavioral modification procedures, a special diet, and an exercise program); explicit inclusion of behavior modification techniques; and focus on children with more severe obesity. The diet should emphasize calorie and fat reduction (tailored to the child's age and metabolic needs), include a simple categorization of foods understood easily by children, and be supervised by a health professional.

More aggressive approaches to weight loss being used in the treatment of adults are under investigation in the treatment of adolescents, including the use of medications, very low calorie diets, and surgery. Until recently, the use of medications in the treatment of obesity has been of relatively little benefit. In the late 1990s, success with medications such as phentermine and fenfluramine, found to decrease appetite or increase satiety, was tempered by the discovery of unexpected and potentially fatal side effects. Two newer medications, sibutramine, an appetite suppressant, and orlistat, a blocker of fat absorption in the intestine, show promising results in adult treatment and are undergoing clinical trials for use in adolescents.

In more extreme situations, caloric intake can be reduced dramatically with the use of very low calorie diets and obesity surgery, but should be considered for adolescents only after completion of puberty. These diets include anywhere from 300 to 800 calories per day, primarily as protein and carbohydrate, and should be instituted only with adequate medical supervision, since severe nutrient deficiencies and medical complications, such as fatal rhythm disturbances of the heart, can accompany them. Surgical treatments either reduce the capacity of the stomach, thereby inducing earlier satiety, or they decrease the length of the bowel, thereby reducing the bowel's capacity to absorb fat from the meal. Significant side effects in terms of abdominal discomfort, diarrhea, and potential nutrient deficiency are common.

With the difficulty in treating obesity at any stage of life, attention is turning toward understanding the possible role of prevention. Efforts are underway to develop behavioral and biochemical approaches to prevention, particularly in children identified as high risk, based on their early growth patterns and family history.

See also: EXERCISE; NUTRITION; PHYSICAL GROWTH

Bibliography

Epstein, Leonard H. "New Developments in Child Obesity." In Albert J. Stunkard and Thomas A. Wadden eds., Obesity. New York: Raven Press, 1993.

Hammer, Lawrence D. "The Development of Eating Behavior inChildhood." Pediatric Clinics of North America 39 (1992):379-394.

Hammer, Lawrence D., and Thomas N. Robinson. "Child and Adolescent Obesity." In Melvin D. Levine ed., Developmental-Behavioral Pediatrics. Philadelphia: Saunders, 1999.

Robinson, Thomas N., and William H. Dietz. "Weight Gain: Overeating to Obesity." In Abraham M. Rudolph ed., Pediatrics. Stamford, CT: Appleton and Lange, 1996.

World Health Organization. Obesity: Preventing and Managing the Global Epidemic. Geneva: World Health Organization, 1997.

Lawrence D. Hammer