Nutritional Aspects of Obesity in Infancy and Childhood

Obesity is characterized by an excess of adipose tissue relative to lean body mass. With rare exceptions, it simply reflects a long-term imbalance in energy intake vs expenditure. The excess energy is stored as fat. The known metabolic correlates of this state are, for the most part, secondary events.1 The day-to-day "error" in intake or expenditure necessary to derange long-term energy balance is smaller than the accuracy with which either factor currently can be measured over long periods; therefore, the question of etiologies remains unanswered. The systems regulating mammalian fuel homeostasis and food intake are complex, and many potential "lesions" could alter long-term energy balance. There are a number of experimental and genetic animal models in which regulatory or apparent metabolic disturbances result in obesity, but no similar abnormalities have been consistently demonstrated in individuals with simple obesity.2 However, the traditionally accepted causes of obesity, relative overeating and/or physical underactivity, may not be operating in all instances of simple obesity.3,4 ANTHROPOMETRY Criteria for the diagnosis of obesity are difficult to establish because "optimal fatness is a conditional state. A man preparing for an emergency trek, a population entering a period of famine, a child entering a febrile illness or a growth spurt or a woman becoming pregnant will have physiological advantages from abundant stored fat."5 Medical considerations suggest that excessive adiposity (or leanness) is unhealthful; but cosmetic and other social considerations are generally preeminent in determining the acceptable range of body composition within a culture. A variety of definitions of obesity have been devised for adults (weight-height indices that produce relative independence of weight from height).