I have read and understood the BMJ Group policy on declaration of interests and declare the following interests: LH is funded by the Wellcome Trust. BDN is funded by the National Institute for Health Research and Cancer Research UK. PA is funded by NIHR Biomedical Research Centre, Oxford, and NIHR Applied Research Collaboration, Oxford and Thames Valley and is an NIHR senior investigator. PA is an investigator in two publicly funded (National Institute for Health Research) trials in which the weight loss intervention was donated by Nestlé Health Sciences and Oviva to the University of Oxford outside the submitted work. PA is an investigator on a trial part funded by Cambridge Weight Plan. None of these associations led to payments to PA personally. The views expressed are those of the author(s) and not necessarily those of the University of Oxford, NHS, NIHR, CRUK, Wellcome, or the Department of Health.