1 School of Health and Population Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK. claire.madigan@sydney.edu.au.
2 The Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders, The University of Sydney, Level 2 Charles Perkin Centre D17, Sydney, NSW, 2006, Australia. claire.madigan@sydney.edu.au.
3 School of Health and Population Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
4 School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK.
5 Nuffield Department of Primary Care Health Sciences, University of Oxford, Radcliffe Observatory Quarter, Woodstock Road, Oxford, OX2 6GG, UK.