Summary The worldwide prevalence of childhood obesity has increased greatly over the past 3 decades. The increasing occurrence in children of disorders, such as type 2 diabetes, is believed to be a consequence of this obesity epidemic. Much progress has been made in understanding the genetics and physiology of appetite control and from this, the elucidation of the causes of some rare obesity syndromes. However, these rare disorders have so far taught us only limited lessons on how to prevent or reverse obesity in most children. Calorie intake and activity recommendations need to be re-assessed and better quantified, on a population level, given the more sedentary life of children today. For individual treatment, the currently recommended calorie prescriptions may be too conservative given the evolving insight on the “energy gap.” Whilst quality of research in both prevention and treatment has improved, there is still a need for high-quality multi-centre trials with long-term follow-up. Meanwhile, prevention and treatment approaches that aim to increase energy expenditure and decrease intake need to continue. Most recently, the spiralling increase in obesity prevalence may be abating for children. Thus, even greater efforts need to be made on all fronts to continue this potentially exciting trend.

Substantial declines in physical activity occur during adolescence in girls and are greater in black girls than in white girls. Some determinants of this decline, such as higher body-mass index, pregnancy, and smoking, may be modifiable.

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The longitudinal data on physical activity collected in the NGHS cohort further confirm a dramatic decrease in the overall level of physical activity during the transition from childhood to adolescence. The consistency among the three methods indicate that both the AD and HAQ are useful tools for the assessment of activity levels in adolescent girls.