"When energy intake exceeds expenditure, the excess calories are stored in adipose tissue, and if this net positive balance is prolonged, obesity results; i.e., there are two components to weight balance, and an abnormality on either side (intake or expenditure) can lead to obesity.
The regulation of eating behavior is incompletely understood. To some extent, appetite is controlled by discrete areas in the hypothalamus: a feeding center in the ventrolateral nucleus of the hypothalamus (VLH) and a satiety center in the ventromedial hypothalamus (VMH). The cerebral cortex receives positive signals from the feeding center that stimulate eating... and the satiety center modulates this process by sending inhibitory impulses to the feeding center. In animals, destruction of the feeding center results in decreased food intake, and destruction of the satiety center leads to overeating and obesity. Several regulatory processes may influence these hypothalamic centers. The satiety center may be activated by the increases in plasma glucose and/or insulin that follow a meal. It is of interest in this regard that the VMH contains insulin receptors and is insulin-sensitive. Meal-induced gastric distention is another possible inhibitory factor.
The total adipose tissue mass also may influence the activity of the hypothalamic centers; i.e., there is a relatively fixed "set point" for body adiposity. An elevated set point may account for the frequent recidivism in obese patients who have lost weight. How the "set point" is established and how the hypothalamus senses total fat stores are unknown. Glycerol release from fat cells, ascending neural impulses, and/or circulation of adipocyte-derived peptides such as adipsin may be signals of adipose tissue size. Additionally, the hypothalamic centers are sensitive to catecholamines, and beta-adrenergic stimulation inhibits eating behavior. This provides at least one rationale for the anorexiant effects of amphetamines.
Ultimately, the cerebral cortex controls eating behavior, and impulses from the feeding center to the cerebral cortex are only one input. Psychological, social, and genetic factors also influence food intake. In many obese subjects these influences are overriding; indeed, obese subjects usually respond to external signals such as time of day, social setting, and smell or taste of food to a greater extent than do persons of normal weight.
Eating disorders generally have their onset in postpubertal adolescents, and adolescents may fulfill the DSM-IIIR criteria for anorexia nervosa or bulimia nervosa prior to the completion of puberty... Adolescents with subclinical eating disorders may need the same treatment as adolescents with full-fledged disorders. The warning signs of emerging eating disorders are listed in Table 7-6 and include major body image problems, difficulty establishing autonomy from the family, perfectionism, and family history of eating disorders including obesity. While the eating patterns in many adolescents appear abnormal, and adolescent girls commonly have dissatisfaction with weight and shape and some fear of gaining weight, these feelings and fears are extreme in the adolescent with an eating disorder..."
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