Obesity

Term describing a condition where the ratio of body fat to total body mass is higher than accepted norms.

Obesity is a relative term used to describe the condition where the ratio of body fat, which is measurable, to total body mass is higher than the accepted norm. {Obesity and overweight are often used interchangeably, but their technical definitions are different. Overweight refers to an excess of body weight that includes all tissues—fat, bone, and muscle. Obesity refers specifically to an excess of body fat.) Body fat is about 15% of total body mass for the normal adult male and about 20-25% for the normal adult female. A general rule of thumb is that an individual is probably obese when his or her weight exceeds the maximum weight on standardized height and weight charts by more than 20%. However, during childhood and adolescence, when the body is growing and developing, the proportion of body fat is slightly higher than for a mature adult. In addition, the proportion of body fat fluctuates during various stages of growth.

The percent of U.S. children who are overweight is estimated to be between 20-30%, but there is no firm definition of obesity for children and adolescents. The body mass index (BMI) and average weight-for-height charts provide general guidelines. Pediatricians and parents should evaluate an individual child's weight in the context of his stage of growth, level of physical activity, and general dietary habits. Richard P. Troiano, a researcher at the Centers for Disease Control and Prevention, encourages parents and physicians to observe children and adolescents in their environment over time, and cautions against making weight a disease. Adults should help children see the relationship between eating and exercise choices and weight.

Some babies are born obese, chiefly the result of diabetic mothers, obese mothers, or mothers with excessive pregnancy weight gains. The causes of neonatal obesity are therefore obvious; excessive insulin produced by the fetus itself in the first case and an excessive supply of transplacental nutrients in the latter cases. Neonatal obesity does not necessarily translate into childhood or later obesity, but there is an increased probability if the obese neonate is born into (or adopted into) an obese family.

Some babies actually become obese because of infant-care workers, grandmothers, or other parent-surrogates. Such care-giving individuals may simply value infant obesity ("a nice plump baby"), or they may use the bottle to quiet the infant, or to demonstrate their own competence as child-rearers. Because infants who are obese on their first birthday may be physically delayed in crawling and walking, they are therefore delayed in attaining the increased energy expenditure that ordinarily goes with toddler-stage activity.

Children of obese parents are more likely to become obese during childhood, and the presence of additional obese family members greatly increases that likelihood. Many studies have shown that the probability of childhood obesity rises with the number of obese family members (including both siblings and grandparents in the count). Though demonstrably familial, childhood and later obesity is not necessarily genetic, as evidenced by adoption studies. Normal weight children adopted into obese families are far more likely to become obese themselves.

Adolescent obesity, in turn, is of particular interest because it is more common for girls than boys, and for low-income adolescent girls in particular. In recent years adolescent obesity has become far more common among girls of Black, Mexican American, Native American and Pacific Island origin.

Though separate childhood-onset, adolescent-onset, and adult-onset obesities have been postulated longitudinal studies that identify the age of onset show that obese people stem from similarly obese family-lines but thatthe adult-onset obese are especially likely to be of low socioeconomic status (SES). Furthermore, obesity may be encouraged by significant partners and peers as well.

In-depth longitudinal studies of the juvenile-onset obese also show parental and peer encouragement to overeat and even deliberate overfeeding of obese children. Concern for the nutrition of obese children carries over to adolescence where some pediatricians may be reluctant to recommend caloric reduction ("intervention") for fear of delaying growth, even when the typical obese adolescent is developmentally well advanced overage-peers!

At all ages, after the first year, obese boys and girls are taller than their nonobese peers, by as much as 10 centimeters at the end of the first decade. Obese boys and girls are also advanced in skeletal maturation (measured as "bone-age"), so they stop growing earlier. Sexual maturation is also advanced in obese boys and girls. It is not uncommon for obese girls to evidence precocious menarche, (early onset of menstruation), sometimes even before the tenth year of life.

It is of course necessary to distinguish between the chronic (or habitual) obese and the newly obese, for the former are much more difficult to restore to a nonobese state and tend to come from families with a larger number of risk factors for obesity. It is also useful to distinguish between the formerly obese and the habitually obese, for the formerly obese are much more likely to revert to obesity (and to come from high-risk families). Summer camps specializing in habitually obese children, especially obese girls, have little long-term success in reducing the level of obesity and a high degree of recidivism for habitual overeating and under-exercise. As an additional problem, parental separation and divorce or other psychological Stressors may stimulate compensatory overeating in previously nonobese children. Moreover, obese teenagers and (increasingly) obese preteens may combine periods of binge eating and caloric deprivation, leading variously to bulimia and anorexia nervosa.

In 1995, the Institute of Medicine published a report that described obesity as a "complex, multifactorial disease of appetite regulation and energy metabolism." The report cited the following outcomes from even relatively moderate weight losses:

• Lower blood pressure (and related lower risk of heart attack and stroke)
• Reduce abnormally high levels of blood glucose
• Lower blood levels of cholesterol and triglycérides (and related lower risk of cardiovascular disease)
• Reduce sleep apnea
• Decrease risk of osteoarthritis of weightbearing joints
• Decrease depression
• Increase self-esteem

Source: "Weighing the Options: Criteria for Evaluating Weight-Management Programs." Washington, DC: Institute of Medicine, telephone: (800) 624-6242.

Hansen, B.C. (eds.). Controversies in Obesity. New York: Praeger Publishers, 1983.

Marin, Roselyn. Helping Obese Children: Weight Control Groups That Really Work. Montreal: Learning Publications, 1990.

Rotatoli, Anthony F., and Robert A. Fox. Obesity in Children and Youth: Measurement, Characteristics, Causes, and Treatment. Springfield, IL: Thomas, 1989.

Garn, S.M. "Continuities and Changes in Fatness from Infancy through Adulthood." Current Problems in Pediatrics 15(2), 1985, pp. 1-47.

Garn, S.M. "Family-Line and Socioeconomic Factors in Fatness and Obesity." Nutrition Reviews 44, 1986, pp. 381-86.

Garn, S.M., T.V. Sullivan, and V.M. Hawthorne. "The Juvenile-Onset, Adolescent-Onset and Adult-Onset Obese." International journal of Obesity 15, 1991, pp. 105-110.

Larkin, Marilynn. "Losing Weight Safely." FDA Consumer 30, January-February 1996, pp. 16-21.

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