1. Department of Public Health Sciences, Norwegian University of Life Sciences , Post Box 5003, 1432 Ås , Norway
2. Department of Community Health Sciences, Cumming School of Medicine, University of Calgary , 3D10, 3280 Hospital Drive NW Calgary, Alberta, T2N 4Z6 Canada
3. Department of Nutrition, Faculty of Medicine, University of Oslo , Sognsvannsveien 9, 0372 Oslo , Norway