Article Text

Download PDFPDF

Intermittent fasting: eating by the clock for health and exercise performance
  1. Sumona Mandal1,
  2. Niall Simmons1,
  3. Sidra Awan2,
  4. Karim Chamari3,
  5. Irfan Ahmed4
  1. 1University College London, Medical School, London, UK
  2. 2University College London Hospitals NHS Foundation Trust, London, UK
  3. 3Aspetar, Orthopaedic and Sports Medicine Hospital, Doha, Qatar
  4. 4Sports Medicine Department, Homerton University Hospital, London, UK
  1. Correspondence to Dr Irfan Ahmed; irfan.ahmed5{at}


Intermittent fasting (IF) is an increasingly popular dietary practice, and its implementation is found throughout human civilisation in various cultural, spiritual and religious traditions. Emerging evidence has shown that the health benefits of IF stretch beyond calorie restriction and weight loss. These benefits include metabolic shifts in energy production, the optimisation of peripheral circadian clocks, and overall improvement in physiological markers of metabolic health. IF has been proposed to reduce systemic inflammation and have a role in the prevention and treatment of chronic disease. For the athlete, IF protocols offer a potential new frontier for maintaining performance in the fasted state. They may allow athletes to optimise training adaptions, while respecting individual cultural, religious, and/or spiritual preferences to fast and exercise. Below, we discuss the physiological impact of fasted exercise while highlighting areas for future work to improve our understanding and implementation of the practice for the benefit of both the active general community and sporting populations.

  • exercise and/or caloric restriction effects on body weight/composition
  • food intake/body weight regulation
  • performance

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See:

Statistics from

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.


  • Twitter @irfan_sem

  • Contributors IA: devised the main conceptional ideas of the manuscript.IA, NS and SM: drafted the manuscript.IA, NS, SM, KC and SA: involved in structuring, researching and editing of the manuscript.I.A approved the final version of the manuscript.SM and NS contributed equally to this paper.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

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