Footnotes

• Twitter Follow Kamal Mahtani at @krmahtani

• Competing interests KRM is an NHS general practitioner who supports and advises patients to lose weight through a healthy balanced diet and regular physical activity. He holds NHS National Institute of Health Research (NIHR) grant funding for some of his research. JMcM is Director of Public Health for Hertfordshire, and a member of the Academy of Medical Royal Colleges Health Inequalities Forum. He is a member of the International Scientific Advisory Group for the Centre for Diet and Activity Research at the University of Cambridge. DN is a senior research fellow and tutor of evidence-based medicine, with a background and research interest in exercise physiology and physical activity. He holds NHS National Institute of Health Research (NIHR) grant funding for some of his research. The views expressed are those of the author(s) and not necessarily those of the NHS National Institute of Health Research (NIHR) or employing institutions.

• Provenance and peer review Not commissioned; internally peer reviewed.