N Michels1, A Verbeiren2, W Ahrens3, S De Henauw4, I Sioen5. 1. Department of Public Health, Faculty of Medicine and Health Sciences, Ghent University, De Pintelaan 185, 2 Blok A, B-9000 Ghent, Belgium. Electronic address: Nathalie.michels@ugent.be. 2. Department of Public Health, Faculty of Medicine and Health Sciences, Ghent University, De Pintelaan 185, 2 Blok A, B-9000 Ghent, Belgium. 3. Bremen Institute for Prevention Research and Social Medicine (BIPS), University of Bremen, Achterstrasse 30, D-28359 Bremen, Germany. 4. Department of Public Health, Faculty of Medicine and Health Sciences, Ghent University, De Pintelaan 185, 2 Blok A, B-9000 Ghent, Belgium; Department of Health Sciences, Vesalius, University College Ghent, Keramiekstraat 80, B-9000 Ghent, Belgium. 5. Department of Public Health, Faculty of Medicine and Health Sciences, Ghent University, De Pintelaan 185, 2 Blok A, B-9000 Ghent, Belgium; Research Foundation - Flanders, Egmontstraat 5, B-1000 Brussels, Belgium.