Intermittent fasting has become a popular health practice in recent years. Although fasting has been practiced by cultures around the world for ages, many people have turned to it for weight loss and for many of its other many reported health benefits. Does it work? Let’s look at what it is and the science behind it.
Intermittent Fasting: What is it?
Intermittent fasting follows a strict program of days eating a normal diet broken up by days where only 25% of one’s dietary calories are consumed. The 5:2 method may be the most popular approach; it’s 5 days of eating with 2 fasting days every week. Some people follow a 4:3 approach. Although there is not set schedule for which days to fast, there is at least one non-fasting day between fasts.
This approach differs from continuous fasting, or continuous caloric restriction, which might also be called traditional dieting. One suggested advantage of intermittent fasting over continuous fasting is that it ensures the body gets the nutrients it needs, even if it is being used to lose weight.
Does Intermittent Fasting Work for Weight Loss?
The research says ‘Yes.’ Even though intermittent fasting doesn’t reduce calories to the same degree as continuous caloric restriction, studies indicate it works as well for fat loss and weight loss.[i],[ii] Intermittent fasting also appears to improve the body’s ability to metabolize fats better.[iii]
Weight loss however is only one of the many apparent benefits of intermittent fasting. Other benefits include:
Support for Heart Health
People who practice intermittent fasting have lower cholesterol and triglyceride levels. The fasting also helps lower these measures of risk for heart disease.[iv],[v] Intermittent fasting also appears to boost HDL levels.[vi]
Protection for the Brain, Memory and Mental Health
Researchers have found intermittent fasting promotes autophagy throughout the body and in the brain too. This encourages neurogenesis which supports memory and cognitive function.[vii]
Intermittent fasting has also been shown to raise levels of BDNF, a brain protein involved in mood and memory.[viii] In one study, individuals who practiced intermittent fasting reported having a better mood and having an overall more positive emotional outlook.[ix]
Better Blood Sugar
People who do intermittent fasting have been shown to have better insulin levels and insulin response. The research also indicates people who struggle with blood sugar may benefit from intermittent fasting to get their blood sugar under control.[x]
Digestive discomfort becomes more regular with age, though conditions like irritable bowels, gas, bloating and indigestion affect people in all age groups. Intermittent fasting appears to aid digestion in a couple of ways. One way may be that every couple of days the digestive tract has less work to do, giving it time to recover. Researchers have also found the fasting appears to trigger stem cells responsible for the regeneration of intestinal lining.[xi]
Appears to Help the Body Reduce Chronic Inflammation
Research in this area is still under a lot of investigation but one study suggested intermittent fasting improves the body’s response to inflammation. The researchers looked at the effect of the fasting on asthma patients. Inflammation in the airways of those who did the fasting improved.[xii]
Fasting also appears to help reduce the inflammation associated with chronic joint pain.[xiii]
Intermittent Fasting May Also Promote Longevity
The absence of food has been shown to turn on sirtuins. These “anti-aging” genes are known for the way they improve antioxidant response, increase metabolic efficiency, improve how the body responds to stress, protect DNA and prompt cellular regeneration. These effects combine in a way that appears to slow the aging process.[xiv]
[i] Wilson RA, et al. Intermittent Fasting with or without Exercise Prevents Weight Gain and Improves Lipids in Diet-Induced Obese Mice. Nutrients. 2018 Mar 12;10(3). pii: E346. doi: 10.3390/nu10030346.
[ii] Tinsley GM, et al. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015 Oct;73(10):661-74. doi: 10.1093/nutrit/nuv041. Epub 2015 Sep 15.
[iii] Antoni, R., Johnston, K., Collins, A., & Robertson, M. (2018). Intermittent v. continuous energy restriction: Differential effects on postprandial glucose and lipid metabolism following matched weight loss in overweight/obese participants. <i>British Journal of Nutrition,</i> <i>119</i>(5), 507-516. doi:10.1017/S0007114517003890
[iv] Tinsley GM, et al. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015 Oct;73(10):661-74. doi: 10.1093/nutrit/nuv041. Epub 2015 Sep 15.
[v] Wilson RA, et al. Intermittent Fasting with or without Exercise Prevents Weight Gain and Improves Lipids in Diet-Induced Obese Mice. Nutrients. 2018 Mar 12;10(3). pii: E346. doi: 10.3390/nu10030346.
[vi] Sundfør TM1, et al. Effect of intermittent versus continuous energy restriction on weight loss, maintenance and cardiometabolic risk: A randomized 1-year trial. Nutr Metab Cardiovasc Dis. 2018 Mar 29. pii: S0939-4753(18)30100-5. doi: 10.1016/j.numecd.2018.03.009. [Epub ahead of print]
[vii] Manzanero S, Erion JR, Santro T, et al. Intermittent fasting attenuates increases in neurogenesis after ischemia and reperfusion and improves recovery. Journal of Cerebral Blood Flow & Metabolism. 2014;34(5):897-905. doi:10.1038/jcbfm.2014.36.
[viii] Mattson MP1, et al. Meal size and frequency affect neuronal plasticity and vulnerability to disease: cellular and molecular mechanisms. J Neurochem. 2003 Feb;84(3):417-31.
[ix] Fitzgerald KC, et al. Effect of intermittent vs. daily calorie restriction on changes in weight and patient-reported outcomes in people with multiple sclerosis. Mult Scler Relat Disord. 2018 May 5;23:33-39. doi: 10.1016/j.msard.2018.05.002. [Epub ahead of print]
[x] Adrienne R. et al. Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research, Volume 164, Issue 4, 2014, Pages 302-311, ISSN 1931-5244.
[xi] Mihaylova MM, et al. Fasting Activates Fatty Acid Oxidation to Enhance Intestinal Stem Cell Function during Homeostasis and Aging. Cell Stem Cell. 2018 May 3;22(5):769-778.e4. doi: 10.1016/j.stem.2018.04.001.
[xii] Johnson JB, Summer W, Cutler RG, et al. Alternate Day Calorie Restriction Improves Clinical Findings and Reduces Markers of Oxidative Stress and Inflammation in Overweight Adults with Moderate Asthma. Free radical biology & medicine. 2007;42(5):665-674. doi:10.1016/j.freeradbiomed.2006.12.005.
[xiii] Müller H1, et al. Fasting followed by vegetarian diet in patients with rheumatoid arthritis: a systematic review. Scand J Rheumatol. 2001;30(1):1-10.
[xiv] Zhu Y1, et al. Metabolic regulation of Sirtuins upon fasting and the implication for cancer. Curr Opin Oncol. 2013 Nov;25(6):630-6. doi: 10.1097/01.cco.0000432527.49984.a3.