Estimates of the prevalence of obesity among adolescents in developed countries varies depending on the country and the criteria used to define obesity. There are few, however, who would argue that the prevalence is low. Moreover, the prevalence is increasing. If we define obesity as a tricep skinfold thickness of greater than the 85th percentile from the US Health and Nutrition Evaluation Survey 11, then the percentage of US adolescents who are obese has increased from 15% in 1970 to 21% in 198021% in (Dietz, 1987. This is of great concern because of the adverse effects of adolescent obesity on social and emotional development (Goodman et al. 1963) and because obesity is implicated in the development of hypertension (Rames et al. 1978) and maturity-onset diabetes mellitus (Medalie et al. 1974). Moreover, approximately 80% of obese adolescents become obese adults (Lloyd et al. 1961) and between half and three-quarters of very obese adults (160% ideal-body-weight) were obese as children (Rimm & Rimm, 1976).As reviewed by Dietz (1983), it is clear that obesity by definition is a state of expanded body energy stores and thus a result of dietary energy intake exceeding energy expenditure, but it is not clear if there is a causal relationship between obesity and excessive energy intake, decreased energy expenditure, or failure to regulate the balance between intake and expenditure.
Energy intakeMost reports indicate the daily energy intake does not differ between obese and non-obese adolescents. For example, Peckos (1953) monitored intake using a 7 d record in eighty-six children classified as endomorphs (stocky or obese), mesomorphs (muscular), or ectomorphs (lean) and reported that the endomorphs had a 15% lower energy intake than the ectomorphs. Hampton et al. (1%7) reported similar results after comparing dietary intakes from four non-consecutive 7 d records in 122 children. Children classified as obese on the basis of body fat content had a lower daily energy intake than those classified as lean or average. Durnin et al. (1979) also compared the reported energy intakes of children below the 10th percentile (thinnest) and children above the 90th percentile (fattest) from a group of 611 adolescents. The obese girls reported lower intakes than the thin girls, while there was no difference between the obese and thin boys.Based on the previously-mentioned energy intake values, as well as numerous similar studies , one is led to the conclusion that the obese have lower energy requirements than the lean, either because of greater efficiency in energy metabolism or because of a difference in physical activity.