Defining Prolonged and Intermittent Fasting: International Consensus on Fasting Terminology

Abstract

Although fasting is increasingly applied to disease prevention and treatment, consensus on terminology is lacking. Using Delphi methodology, an international, multidisciplinary panel of researchers and clinicians standardized definitions of various fasting approaches. Five online surveys and a live online conference were conducted with 38 experts, 25 of whom completed all five surveys [Europe (n=12), North America (n=12), Australia (n=1)]. Consensus was achieved for the terms: ”fasting” (voluntary abstinence from some or all foods or foods and beverages), “modified fasting” (restriction of energy intake to max. 25% of energy needs), “fluid-only fasting”, “alternate-day fasting”, “short-term fasting” (lasting 1-3 days), “prolonged fasting” (≥4 consecutive days) and “religious fasting”. “Intermittent fasting” (repetitive fasting periods lasting ≤48 h), “time-restricted eating” and “fasting-mimicking diet” were discussed most. This study provides expert recommendations on fasting terminology for future research and clinical applications, facilitating communication and cross-referencing in the field.

Funding Information: Financial support for this project was provided by Immanuel Hospital Berlin.

Conflict of Interests: Daniela A. Koppold and Andreas Michalsen are members of the steering committee of the Medical Association for Fasting and Nutrition (ÄGHE). D.A.K. has co-founded the Academy of Integrative Fasting (AIF), an institution for the qualification of medical staff in clinical fasting applications. D.A.K. serves as a consultant for a mobile application on intermittent fasting (FASTIC) as well as a company producing plant-based supplements (EVERYYIN). A.M. is also Co-founder of the SALUFAST company. A.M. serves as a consultant for Lanserhof. Etienne Hanslian and Anika Rajput-Khokhar are members of the steering committee of the Medical Association for Fasting and Nutrition (ÄGHE). Courtney Peterson has no conflicts of interest. C.P. receives grant funding from the National Institutes of Health and the Department of Defense to study intermittent fasting. Grant Tinsley is an inventor on the international patent “Compositions and methods of use of beta-hydroxy beta-methylbutyrate (HMB) associated with intermittent fasting.” Claudio Vernieri is on the advsory board for Novartis, Eli Lilly, Pfizer, Menarini and Daiichi Sankyo. He receives honoraria as a speaker from Novartis, Eli Lilly, Istituto Gentili, Accademia di Medicina and research grants from Roche.C.V. is supported by AIRC (Associazione Italiana per la ricerca sul Cancro) MFAG 22977, ERC (European Research Council) METABALANCANCER - 101117893, Giuliani Foundation: Fondazione Gianmaria e Sabrina Giuliani Richard J. Bloomer is a consultant to CalerieHealth and Tecton, and coauthor of The Daniel Cure: The Daniel Fast Way to Vibrant Health. Kelsey Gabel has no conflict of interest. K.G. disclosed receipt of the following financial support: the National Institutes of Health [12HD101373 and 5P30AG022849] Alan C. Goldhamer owns a facility that offers fasting supervision. He is on the board of a non-profit that performs research on fasting in humans and he is the owner of TrueNorth Health Center and the president of the board of the TrueNorth Health Foundation. Michelle Harvie has co-authored three self-help books for the public to follow intermittent diets. All author proceeds are paid directly to the charity Prevent Breast Cancer (registered charity number 1109839) to fund breast cancer research. M.H. undertakes paid webinars for Nestlé Health Science and Oviva. All payments are made to Manchester University Foundation Trust. Benjamin D. Horne is a member of the advisory boards of Opsis Health and Lab Me Analytics, a consultant to Pfizer regarding risk scores (funds paid to Intermountain), and site PI of grants (not related to fasting) from the Patient-Centered Outcomes Research Institute, the NIH RECOVER initiative, and the Task Force for Global Health. Jost Langhorst offers consulting and expert activities to Medizinverlage Stuttgart; Ferring Arzneimittel GmbH; Repha GmbH; Dr. Willmar Schwabe. He receives honoraria as a speaker from Falk Foundation; Repha GmbH biologische Arzneimittel; Dr. Willmar Schwabe; Galapagos Pharma, Takeda Pharmaceutical, Janssen Cilag, Dr. Pfleger Arzneimittel, Bristol-Myers Squibb GmbH, Bionorica, Luvos Just GmbH, Pfitzer Pharma GmbH and Enterosan Labordiagnostik. J.L. receives research funding from Falk Foundation, Dr. Willmar Schwabe, Repha GmbH biologische Arzneimittel, TechLab. Frank Madeo has equity interests in and is advisor of The Longevity Labs (TLL) and is a scientific cofounder of Samsara Therapeutics. F.M. is grateful to the Austrian Science Fund FWF (F3012, W1226, P31727, P37016, P 37278) and the Austrian Federal Ministry of Education, Science and Research as well as the University of Graz for grants ‘Unkonventionelle Forschung-InterFast and Fast4Health'. We acknowledge the support of the Field of Excellence BioHealth of NAWI Graz and the BioTechMed-Graz flagship project ‘EPIAge'. Ioannis-Eleemon Papagiannopoulos-Vatopaidinos has no conflicts of interest. Martha Ritzmann-Widderich is a member of the board of the Medical Association for Fasting and Nutrition (ÄGHE). Krista Varady received author fees from Hachette Book Group for The Every Other Day Diet. Rafael de Cabo has no conflicts of interest. R.d.C. is supported in part by the Intramural Research Program at the NIA, National Institutes of Health. Valter Longo has equity interest in L-Nutra Inc., a company that markets and sells the FMD. USC has licensed intellectual property to L-Nutra and as part of this license agreement, the University has the potential to receive royalty payments from L-Nutra. One-hundred percent of V.D.L.’s equity is assigned to the nonprofit foundation Create Cures. Satchidananda Panda is the author of the books "The Circadian Code" and "The Circadian Diabetes Code". Rainer Stange is member of Medical Association for Fasting and Nutrition (ÄGHE), president of National Association of Physicians for Natural Medicine (ZAEN), has received honoraries for conduct of clinical trials, consulting and lectures from Repha GmbH Biologische Arzneimittel, Langenhagen, germany, mediconomics GmbH, Hannover, Germany S.A. Vogel, Roggwil, Switzerland, Clinica Holistica Engiadina, Susch, Switzerland, Roleca Pharma GmbH, Hannover, Germany. Remaining authors have no conflict of interest.

Ethical Approval: The study protocol was approved by the institutional review board of Charité - Universitätsmedizin Berlin (Charitéplatz 1, 10117 Berlin) in February 2022 (ID: EA4/028/22). The study was registered with ClinicalTrials.gov (ClinicalTrials ID: NCT05668156) and conducted according to the standards of the Declaration of Helsinki. Written informed consent was obtained from all participants prior to study entry.

Keywords: Delphi method, fasting, periodic fasting, intermittent fasting, fasting-mimicking diet, dry fasting, therapeutic fasting, intermittent energy restriction, time-restricted eating, alternate-day fasting