Intermittent fasting

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Intermittent fasting (IF), or intermittent calorie restriction, is an umbrella term for various diets that cycle between a period of fasting and non-fasting during a defined period. Intermittent fasting may produce weight loss comparable to long-term calorie restriction.[1][2][3][4]

Practice and variants[edit]

Intermittent fasting can be a viable strategy to reduce caloric intake, body weight, body fat mass, and improve insulin sensitivity.[1][3][4][5][6] Intermittent fasting protocols can be grouped into two categories: whole-day fasting and time-restricted feeding.

  • Whole-day fasting involves regular one-day fasts. The strictest form would be alternate day fasting (ADF). This involves a 24-hour fast followed by a 24-hour non-fasting period.[7] The alternate day modified fasting (ADMF) and 5:2 diets - the latter defined as five days per week not fasting and two days per week either total fasting or modified fasting - both allow the consumption of approximately 500–600 calories on fasting days.[1][3][8][9]
  • Time-restricted feeding (TRF) involves eating only during a certain number of hours each day.[10] A common form of TRF involves fasting for 16 hours each day and only eating during the remaining 8 hours, typically on the same schedule each day.[11] A more liberal practice would be 12 hours of fasting and a 12 hour eating window, or a stricter form would be to eat one meal per day, which would involve around 23 hours of fasting per day.[12]

Recommendations vary on what can be consumed during the fasting periods. Some would say only water, others would allow tea or coffee (without milk or sugar) or zero-calorie drinks with artificial sweeteners. Fasting may increase a risk of dehydration.[13] Variants include modified fasting, such as ADMF, with limited caloric intake (20% of normal) during fasting periods rather than none at all, in order to improve tolerance and mood.[1][3] Intermittent fasting has a different duration (up to 48 hours) than periodic fasting (2 or more days).[1][14]


Alternate day fasting was effective for weight loss on a scale similar to calorie restriction.[2][3][15] Weight loss was observed in both obese and normal weight people.[4] Preliminary evidence indicates that improvements in several cardiovascular and metabolic biomarkers (such as body fat, LDL cholesterol, triglycerides, insulin sensitivity, blood pressure) occurred.[6][16][17] Alternate day fasting did not affect lean body mass.[2][3][4] Contrary to calorie restriction, weight loss was more reliably maintained with alternate day fasting over the medium to long term.[2][3] A 2014 review described that intermittent fasting has not been studied in children, the elderly, or the underweight, and could be harmful in these populations.[18] Intermittent fasting may reduce rapid eye movement sleep,[1][17] but other effects on brain function remain undetermined.[18][19]

Intermittent fasting is associated with increased hunger and decreased feelings of fullness. For this reason, ADMF, with a reduced calorie intake during fasting days (instead of none), was proposed as being better tolerated and maintained, in particular by increasing the feelings of fullness. Although ADMF may be effective for weight loss, this scheme showed mixed effects on biomarkers.[1][3][16]

There are several variants of intermittent fasting diets under preliminary research, with varying results. Some studies found that fasting may improve biomarkers and weight loss from 8-12 hours during the fast, with a peak in body fat loss and decrease in glucose loss at 18-24 hours, although these effects are not proven. Resting metabolism (i.e., more energy consumed at rest) increased at 36-48 hours, but the metabolic effects of other durations of fasting have not been reported.[4] Time-restricted diets provided lower long-term weight loss compared to other variants.[1][3][16][20] Religious fasts are also under limited research, with no confirmation of efficacy.[1][21][22]

Popular culture[edit]

The 5:2 diet became popular in the UK in 2012[23][24][25] after the BBC2 television Horizon documentary Eat, Fast and Live Longer.[26] Via sales of best-selling books, it became widely practiced.[9][27] According to NHS Choices as of 2012, people considering the 5:2 diet should first consult a physician, as fasting can sometimes be unsafe.[9][28] In the UK, the tabloid press reported on research claiming the 5:2 diet could reduce the risk of breast cancer, improve brain and immune functions, or extend lifespan, but there is inadequate evidence for such statements.[9][29] A news item in the Canadian Medical Association Journal expressed concern that promotional material for the diet showed people eating high-calorie food such as hamburgers and chips, and that this could encourage binge eating since the implication was that "if you fast two days a week, you can devour as much junk as your gullet can swallow during the remaining five days".[30]

See also[edit]


  1. ^ a b c d e f g h i Patterson, Ruth E.; Sears, Dorothy D. (21 August 2017). "Metabolic Effects of Intermittent Fasting". Annual Review of Nutrition. 37 (1): 371–393. doi:10.1146/annurev-nutr-071816-064634. 
  2. ^ a b c d Davis, C S; Clarke, R E; Coulter, S N; Rounsefell, K N; Walker, R E; Rauch, C E; Huggins, C E; Ryan, L (25 November 2015). "Intermittent energy restriction and weight loss: a systematic review". European Journal of Clinical Nutrition. Nature. 70 (3): 292–299. doi:10.1038/ejcn.2015.195. 
  3. ^ a b c d e f g h i j Johnstone, A (26 December 2014). "Fasting for weight loss: an effective strategy or latest dieting trend?". International Journal of Obesity. Nature. 39 (5): 727–733. doi:10.1038/ijo.2014.214. 
  4. ^ a b c d e Tinsley, Grant M.; La Bounty, Paul M. (October 2015). "Effects of intermittent fasting on body composition and clinical health markers in humans". Nutrition Reviews. 73 (10): 661–674. doi:10.1093/nutrit/nuv041. 
  5. ^ Patterson, R. E; Laughlin, G. A; Lacroix, A. Z; Hartman, S. J; Natarajan, L; Senger, C. M; Martínez, M. E; Villaseñor, A; Sears, D. D; Marinac, C. R; Gallo, L. C (2015). "Intermittent Fasting and Human Metabolic Health". Journal of the Academy of Nutrition and Dietetics. 115 (8): 1203–1212. doi:10.1016/j.jand.2015.02.018. ISSN 2212-2672. PMC 4516560Freely accessible. PMID 25857868. 
  6. ^ a b Mattson, M. P; Longo, V. D; Harvie, M (2017). "Impact of intermittent fasting on health and disease processes". Ageing Research Reviews. 39: 46–58. doi:10.1016/j.arr.2016.10.005. PMC 5411330Freely accessible. PMID 27810402. 
  7. ^ Varady, K. A (2011). "Intermittent versus daily calorie restriction: Which diet regimen is more effective for weight loss?". Obesity Reviews. 12 (7): e593–601. doi:10.1111/j.1467-789X.2011.00873.x. PMID 21410865. 
  8. ^ Fisher, Roxanne (1 June 2016). "What is the 5:2 diet?". BBC GoodFood, Worldwide. 
  9. ^ a b c d Fleming, Amy (27 January 2015). "Fasting facts: is the 5:2 diet too good to be true?". The Guardian. Retrieved 18 January 2018. 
  10. ^ Rothschild, Jeff; Hoddy, Kristin K; Jambazian, Pera; Varady, Krista A (2014). "Time-restricted feeding and risk of metabolic disease: A review of human and animal studies". Nutrition Reviews. 72 (5): 308–18. doi:10.1111/nure.12104. PMID 24739093. 
  11. ^ Moro, Tatiana; Tinsley, Grant; Bianco, Antonino; Marcolin, Giuseppe; Pacelli, Quirico Francesco; Battaglia, Giuseppe; Palma, Antonio; Gentil, Paulo; Neri, Marco; Paoli, Antonio (2016). "Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males". Journal of Translational Medicine. 14 (1): 290. doi:10.1186/s12967-016-1044-0. PMC 5064803Freely accessible. PMID 27737674. 
  12. ^ Stote, KS; Baer, DJ; Spears, K; Paul, DR; Harris, GK; Rumpler, WV; Strycula, P; Najjar, SS; Ferrucci, L; Ingram, D. K.; Longo, D. L.; Mattson, M. P. (2007). "A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults" (PDF). The American Journal of Clinical Nutrition. 85 (4): 981–8. PMC 2645638Freely accessible. PMID 17413096. 
  13. ^ CNN, Lisa Drayer (March 23, 2018). "How to succeed at intermittent fasting". CNN. Retrieved 30 July 2018. 
  14. ^ Mattson, Mark P.; Longo, Valter D.; Harvie, Michelle (October 2017). "Impact of intermittent fasting on health and disease processes". Ageing Research Reviews. 39: 46–58. doi:10.1016/j.arr.2016.10.005. 
  15. ^ Harris, Leanne; Hamilton, Sharon; Azevedo, Liane B.; Olajide, Joan; De Brún, Caroline; Waller, Gillian; Whittaker, Vicki; Sharp, Tracey; Lean, Mike; Hankey, Catherine; Ells, Louisa (February 2018). "Intermittent fasting interventions for treatment of overweight and obesity in adults". JBI Database of Systematic Reviews and Implementation Reports. 16 (2): 507–547. doi:10.11124/JBISRIR-2016-003248. 
  16. ^ a b c Anton, Stephen D.; Moehl, Keelin; Donahoo, William T.; Marosi, Krisztina; Lee, Stephanie A.; Mainous, Arch G.; Leeuwenburgh, Christiaan; Mattson, Mark P. (February 2018). "Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting". Obesity. 26 (2): 254–268. doi:10.1002/oby.22065. PMC 5783752Freely accessible. PMID 9086496. 
  17. ^ a b Almeneessier, Aljohara S.; Pandi-Perumal, Seithikurippu R.; BaHammam, Ahmed S. (19 July 2018). "Intermittent Fasting, Insufficient Sleep, and Circadian Rhythm: Interaction and Effects on the Cardiometabolic System". Current Sleep Medicine Reports. doi:10.1007/s40675-018-0124-5. 
  18. ^ a b Longo, Valter D; Mattson, Mark P (2014). "Fasting: Molecular Mechanisms and Clinical Applications". Cell Metabolism. 19 (2): 181–92. doi:10.1016/j.cmet.2013.12.008. PMC 3946160Freely accessible. PMID 24440038. 
  19. ^ Cherif, Anissa; Roelands, Bart; Meeusen, Romain; Chamari, Karim (5 October 2015). "Effects of Intermittent Fasting, Caloric Restriction, and Ramadan Intermittent Fasting on Cognitive Performance at Rest and During Exercise in Adults". Sports Medicine. 46 (1): 35–47. doi:10.1007/s40279-015-0408-6. PMID 26438184. 
  20. ^ Koehler, K; De Souza, M J; Williams, N I (26 October 2016). "Less-than-expected weight loss in normal-weight women undergoing caloric restriction and exercise is accompanied by preservation of fat-free mass and metabolic adaptations" (Full text). European Journal of Clinical Nutrition. 71 (3): 365–371. doi:10.1038/ejcn.2016.203. PMID 27782114. 
  21. ^ Persynaki, Angeliki; Karras, Spyridon; Pichard, Claude (March 2017). "Unraveling the metabolic health benefits of fasting related to religious beliefs: A narrative review". Nutrition. 35: 14–20. doi:10.1016/j.nut.2016.10.005. PMID 28241983. 
  22. ^ Adawi, Mohammad; Watad, Abdulla; Brown, Stav; Aazza, Khadija; Aazza, Hicham; Zouhir, Mohamed; Sharif, Kassem; Ghanayem, Khaled; Farah, Raymond; Mahagna, Hussein; Fiordoro, Stefano; Sukkar, Samir Giuseppe; Bragazzi, Nicola Luigi; Mahroum, Naim (27 November 2017). "Ramadan Fasting Exerts Immunomodulatory Effects: Insights from a Systematic Review". Frontiers in Immunology. 8. doi:10.3389/fimmu.2017.01144. 
  23. ^ "How to diet". Live Well - NHS Choices. UK National Health Service. 9 December 2011. Retrieved 10 February 2014. 
  24. ^ Trueland, Jennifer (2013). "Fast and effective?". Nursing Standard. 28 (16): 26–7. doi:10.7748/ns2013. PMID 24345130. 
  25. ^ Healy A (11 June 2013). "Dietitians warn against fad diets". Irish Times. 
  26. ^ Mosley, Michael (5 September 2012). "Eat, Fast & Live Longer". Horizon. Episode 49x03. BBC. 2. Retrieved 10 February 2014. 
  27. ^ "The UK's Hot New 5:2 Diet Craze Hits The U.S. - Weight Loss Miracle?". Forbes. 17 May 2013. Retrieved 10 February 2014. 
  28. ^ "News analysis: Does the 5:2 intermittent fasting diet work?". Health News. UK National Health Service - NHS Choices. May 2013. Retrieved 23 November 2016. 
  29. ^ "Could 5:2 diet play a role in preventing breast cancer?". NHS Choices. 17 June 2016. 
  30. ^ Collier, R (2013). "Intermittent fasting: The science of going without". Canadian Medical Association Journal. 185 (9): E363–4. doi:10.1503/cmaj.109-4451. PMC 3680567Freely accessible. PMID 23569168.