All authors read and approved the final manuscript. Disclaimer The EHES Pilot Project has received funding from the European Commission/Health and Consumers. The views expressed here are those of the authors and they do not represent Commission��s the following site official position. Supplementary Material Additional file 1: Sites and key personnel contributing to the EHES Pilot Project. Click here for file(28K, doc) Acknowledgements A list of sites and key personnel contributing to the EHES Pilot Project is available in the Additional file 1. EHES Joint Action has received funding from the European Commission (Grant agreement number 2009-23-01). The EHES Reference Centre is funded by the European Commission through a Service Contract (SANCO/2008/C2/02-SI2.538318 EHES).

The influence of chronic stress on changes in body composition is investigated over a two-year follow-up period (February-June 2010, 2011 and 2012) in primary-school children between 6 and 12years old in the city Aalter (Flanders, Belgium). Stress is measured by child- and parent-reported stress-questionnaires, as well as by objective stress biomarkers (serum, salivary and hair cortisol) and heart rate variability. Body composition is evaluated using basic anthropometric measurements and air displacement plethysmography. Additional information on socio-economic status, medical history, physical activity, dietary intake and sleep are obtained by questionnaires, and physical activity by accelerometers. Results The participation percentage was 68.7% (N=523/761), with 71.3% of the children willing to participate in the first follow-up survey.

Drop-out proportions were highest for serum sampling (12.1%), salivary sampling (8.3%) and heart rate variability measurements (7.4%). Discussion The ChiBS project is unique in its setting: its standardized and longitudinal approach provides valuable data and new insights into the relationship between stress and changes in body composition in a large cohort of young children. In addition, this study allows an in-depth investigation of the validity of the different methods that were used to assess stress levels in children. Keywords: Stress, Child, Body composition, Obesity, Cortisol, Heart rate variability, Questionnaire, Food habits, Physical activity, Sleep Background The last decades have been characterized by a global growing obesity epidemic, starting already in childhood [1,2].

World-wide at least 110 million children are overweight or obese [2]. In the European Union, the prevalence of childhood overweight and obesity ranges from 10-20% (northern European areas) to 20-40% (Mediterranean Sea countries) and is expected to rise by 1.3 million children per year [3]. These numbers stress the importance of a better understanding of the Batimastat complex etiology of obesity in order to help developing effective prevention programs.