What is Intermittent Fasting, and Does it Really Work?

  • January 13, 2020

Intermittent fasting (IF) is a way of eating that involves short-term fasting. There are many health benefits now documented in the research with IF. Here are three popular ways to achieve the results:

  • The 16/8 Method: Basically, you skip breakfast every day and have an eating window of 8 hours or from 12:00 (noon) to 8:00 pm.
  • Eat-Stop-Eat: Do one of two 24 hour fasts each week by not eating from dinner one day to dinner the next day.
  • The 5:2 Eating Strategy: Only eat 500-600 calories on two days of the week and then eat normally the other 5 days.

Why has IF grown in popularity? There are numerous studies that show the benefits of the IF eating pattern, where you cycle between periods of eating and fasting. Here is some of the current research:

  1. Insulin levels drop significantly, which facilitates fat burning (1).
  2. The blood levels of human growth hormone may increase as much as 5-fold (2), (3) which facilitates fat burning and muscle gain along with other numerous health related benefits (4), (5).
  3. The body induces important cellular repair processes, such as removing waste material from cells (6).
  4. IF enhances hormone function to facilitate weight loss.
  5. Short-term fasting actually increases your metabolic rate by 3.6-14%, helping you to burn more calories (10) (11).
  6. Unless you compensate by eating much more during times when you are not fasting, you will take in fewer calories. Therefore, IF helps to decrease calories taken in and increase metabolic rate.
  7. People lost 4-7% of their waist circumference, indicating that they lost belly fat (12).
  8. A review study showed that IF caused less muscle loss than continuous calorie restriction (13).
  9. In human studies, IF has been shown to have major benefits for insulin resistance and lead to an impressive reduction in blood sugar levels (12).
  10. Recent studies have shown that IIF can help fight inflammation which is another driver of many common diseases (17), (18), (19).
  11. IF has been shown to improve numerous risk factors, including blood pressure, total and LDL cholesterol, triglycerides, inflammatory markers and blood sugar levels (12), (21).
  12. IF increases the growth of new nerve cells, which have benefits for brain function (32).
  13. In a series of case reports, IF was able to significantly improve Alzheimer’s symptoms in 9 out of 10 patients (39).


(1) Am J Clin Nutr. 2005 Jan;81(1):69-73. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. Heilbronn LK1, Smith SR, Martin CK, Anton SD, Ravussin E.

(2) J Clin Invest. 1988 Apr; 81(4): 968–975. Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man. K Y Ho, J D Veldhuis, M L Johnson, R Furlanetto, W S Evans, K G Alberti, and M O Thorner.

(3) J Clin Endocrinol Metab. 1992 Apr;74(4):757-65. Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men. Hartman ML1, Veldhuis JD, Johnson ML, Lee MM, Alberti KG, Samojlik E, Thorner MO.

(4) JAMA. 2002 Nov 13;288(18):2282-92. Growth hormone and sex steroid administration in healthy aged women and men: a randomized controlled trial. Blackman MR1, Sorkin JD, Münzer T, Bellantoni MF, Busby-Whitehead J, Stevens TE, Jayme J, O’Connor KG, Christmas C, Tobin JD, Stewart KJ, Cottrell E, St Clair C, Pabst KM, Harman SM.

(5) N Engl J Med. 1990 Jul 5;323(1):1-6. Effects of human growth hormone in men over 60 years old. Rudman D1, Feller AG, Nagraj HS, Gergans GA, Lalitha PY, Goldberg AF, Schlenker RA, Cohn L, Rudman IW, Mattson DE.

(6) Autophagy. 2010 Aug 16; 6(6): 702–710. Published online 2010. Short-term fasting induces profound neuronal autophagy Mehrdad Alirezaei,#1 Christopher C. Kemball,#1 Claudia T. Flynn,1 Malcolm R. Wood,2 J. Lindsay Whitton, 1 and William B. Kiosses.

(10) Am J Physiol. 1990 Jan;258(1 Pt 2):R87-93. Enhanced thermogenic response to epinephrine after 48-h starvation in humans. Mansell PI1, Fellows IW, Macdonald IA.

(11) Am J Clin Nutr. 2000 Jun;71(6):1511-5. Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. Zauner C1, Schneeweiss B, Kranz A, Madl C, Ratheiser K, Kramer L, Roth E, Schneider B, Lenz K.

(12) Translational Research. Oct 2014. Volume 164 (4). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Pages 302-311.

(13) Obes Rev. 2011 Jul;12(7):e593-601. doi: 10.1111/j.1467-789X.2011.00873.x. Epub 2011 Mar 17. Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? Varady KA.

(17) Free Radic Biol Med. 2007 Mar 1;42(5):665-74. Epub 2006 Dec 14. Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Johnson JB1, Summer W, Cutler RG, Martin B, Hyun DH, Dixit VD, Pearson M, Nassar M, Telljohann R, Maudsley S, Carlson O, John S, Laub DR, Mattson MP.

(18) Ann Nutr Metab. 2007;51(1):88-95. Epub 2007 Mar 19. Interleukin-6, C-reactive protein and biochemical parameters during prolonged intermittent fasting. Aksungar FB1, Topkaya AE, Akyildiz M.

(19) Nutr Res. 2012 Dec;32(12):947-55. doi: 10.1016/j.nutres.2012.06.021. Epub 2012 Oct 4. Intermittent fasting during Ramadan attenuates proinflammatory cytokines and immune cells in healthy subjects. Faris MA1, Kacimi S, Al-Kurd RA, Fararjeh MA, Bustanji YK, Mohammad MK, Salem ML.

(21) Am J Clin Nutr. 2009 Nov;90(5):1138-43. doi: 10.3945/ajcn.2009.28380. Epub 2009 Sep 30. Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. Varady KA1, Bhutani S, Church EC, Klempel MC.

(32) J Mol Neurosci. 2000 Oct;15(2):99-108. Dietary restriction increases the number of newly generated neural cells, and induces BDNF expression, in the dentate gyrus of rats.Lee J1, Duan W, Long JM, Ingram DK, Mattson MP

(39) Reversal of cognitive decline: A novel therapeutic program. Dale E. Bredesen, Mary S. Easton Center for Alzheimer’s Disease Research, Department of Neurology, University of California, Los Angeles, CA 90095; Buck Institute for Research on Aging, Novato, CA 94945