[Required Effekt Sizes of Preventive Measures for Overweight in Children and Adolescents]

Successful preventive measures can stop a further increase in the prevalence of overweight in children and adolescents. However, up to now, the required effect sizes of interventions for reducing childhood overweight remain unclear. The calculation of the energy gap (excess calories consumed over calories expended) offers the possibility to estimate the required effect sizes. In this work 2 approaches to calculate the energy gap will be compared.

Longitudinal data of 1690 children and adolescents of the Kiel Obesity Prevention Study (KOPS) on measured height, weight, fat mass and fat-free mass (using bioelectrical impedance analysis) at age 6 and 10 years will be used to calculate energy gap with 2 different approaches: (i) using age-independent changes in fat mass and fat-free mass (old approach) and (ii) using a mathematic model of weight dynamic (new approach).

Energy gap according to the old approach was 140 kcal/day; by contrast, new modeling resulted in an energy gap between 270 and 370 kcal/day. Both, BMI and fat mass were suitable to calculate energy gap and led to nearly same results. Exceeding the 90(th) percentile of BMI or fat mass (incidence approach) as well as large changes within the normal range (i.e. between the 10(th) and the 90(th) percentile) led to large energy gaps. Thus, all children with large energy gaps have to be characterized as at risk for overweight.

The new approach seems to be convincing because it considered the additional energy expenditure for building fat-free mass due to increasing age and weight.Calculating energy gap offers a new approach for prevention of overweight. It shows that the required effect sizes of prevention measures have to be in a region of 140 to 400 kcal/day. This differs clearly from energy reduction of diets in the therapy of obesity.