Alternate Day Fasting: All You Need to Know

Alternate day fasting is a popular intermittent fasting method. Read on to learn how it works and what the pros and cons are.
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Alternate day fasting is a popular dietary strategy. But many of you might be wondering what alternate day fasting is and what some of the pros and cons are. In this article, we define alternate day fasting and what it means to adhere to this dietary pattern as well as the various benefits and drawbacks.

Written by
Christine Richardson, PhD
Clinical Project Manager at Becton Dickinson

Different variations of intermittent fasting are extremely popular among people trying to lose weight and people trying to reduce their risk of metabolic diseases, like 16/8 or 18/6 fasting or even 20/4 fasting.

One form is alternate day fasting. Because alternate day fasting is a pretty extreme version of intermittent fasting, many people might claim that it is a form of disordered eating. However, that isn’t necessarily true. 

Alternate day fasting can be a part of a healthy lifestyle and can help you lose weight while improving your overall health.

In this article, we will discuss what alternate day fasting is along with some pros and cons of this dietary pattern.

What is Alternate Day Fasting?

Alternate day fasting is where you alternate between days of fully fasting and days where you can eat whatever you’d like. 

While the concept sounds easy, actually practicing this might be challenging for some because you do go a full day without eating. Some people choose to practice a modified version of alternate day fasting where they eat one meal that usually consists of about 500 calories on their fasting days. 

Studies have shown that modified alternate day fasting can also facilitate weight loss and improvements in health (1,2). This means that taking the modified approach is nothing to be ashamed of.

This modified approach is also a good strategy to implement if you are new to alternate day fasting and find it difficult to not eat for an entire day. Try a modified approach for a couple weeks and then transition to fully fasted days.

One thing to make note of is that if you decide to try alternate day fasting, make sure you are eating enough on your non-fasting days. Determine how many calories you should eat based on your sex, height, weight, age, and activity level and aim to consume that as a minimum. You do not want your overall caloric intake to decrease too much.

Benefits of Alternate Day Fasting

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There are many potential benefits to alternate day fasting. 

  1. The first is weight loss. Studies have shown time and time again how this form of fasting, and even the modified version, is very effective at helping individuals lose weight (3,4).

  1. Alternate day fasting is also effective at causing autophagy. Autophagy is where the older parts of your cells are degraded and recycled. This has been shown to be involved with reducing the risk of various diseases like Alzheimer’s and Parkinson’s, cancer, cardiovascular disease, as well as decreasing inflammation (5,6,7).

  1. Alternate day fasting can also help decrease your risk of cardiovascular disease. Studies have shown that this form of fasting can decrease the risk of atherosclerosis while decreasing blood pressure, triglycerides, and cholesterol levels (3,4).

  1. Lastly, this type of fasting can help decrease your risk of type 2 diabetes. Studies have shown that alternate day fasting decreases blood sugar levels and increases insulin sensitivity (8). 

While more studies are needed, it appears that alternate day fasting, or the modified version, may be a superior alternative to caloric restriction for decreasing blood sugar levels (9).

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Cons to Alternate Day Fasting

  1. The most obvious drawback to this type of diet is how difficult it may be. Going a full day without any food may cause you to be grumpy and tired. Other people report feelings of nausea or headaches when they go too long without eating. 

While most people report that these feelings will eventually go away after your body adapts, the first few weeks may be a struggle. This is why starting out with a modified alternate day fasting approach may be a good strategy.

Another idea is to find a buddy or a group that are doing alternate day fasting too. Having a support system is always an effective strategy for cultivating long-term habits.

  1. Another con to this diet is that it might not be sustainable for people long term. Are you someone who enjoys social outings like dinners and drinks? If so, you may not be able to participate in some social get-togethers if they fall on one of your fasting days. Sure, you can definitely go, but you can’t eat or consume alcohol like your friends and family. This might be really difficult for some people. Of course, you could be a little flexible on your fasting days to try to maintain your social life...that’s entirely up to you!

  1. Lastly, if you are an athlete or like to work out daily, this diet may be difficult for you. Working out combined with a long-term fast can lead to a decrease in muscle mass and performance as well as cause feelings of fatigue and irritability (10). If you are an athlete or a very active individual, alternate day fasting may not be the right form of fasting for you.

  1. Other individuals who probably shouldn’t try alternate day fasting are pregnant women or women trying to become pregnant, lactating women, people who have had disordered eating habits, and people who are underweight and/or have a low body mass index (BMI). Talk to your doctor before trying alternate day fasting to make sure you can do this safely.

The Bottom Line

Alternate day fasting is an extreme and potentially difficult version of intermittent fasting. However, if done correctly, it can be a very effective strategy for losing weight and optimizing your health.

Hesitating with OMAD ? Check out our article comparing alternate day fasting and OMAD.


1. Eshghinia S, Mohammadzadeh F. The effects of modified alternate-day fasting diet on weight loss and CAD risk factors in overweight and obese women. J Diabetes Metab Disord [Internet]. Springer; 2013 [cited 2021 Jun 24];12:4. Available from: /pmc/articles/PMC3598220/

2. Varady KA, Bhutani S, Church EC, Klempel MC. Short-term modified alternate-day fasting: A novel dietary strategy for weight loss and cardioprotection in obese adults. Am J Clin Nutr [Internet]. Am J Clin Nutr; 2009 [cited 2021 Jun 24];90:1138–43. Available from:

3. Cui Y, Cai T, Zhou Z, Mu Y, Lu Y, Gao Z, Wu J, Zhang Y. Health Effects of Alternate-Day Fasting in Adults: A Systematic Review and Meta-Analysis [Internet]. Frontiers in Nutrition. Frontiers Media S.A.; 2020 [cited 2021 Jun 2]. p. 586036. Available from: /pmc/articles/PMC7732631/

4. Park J, Seo YG, Paek YJ, Song HJ, Park KH, Noh HM. Effect of alternate-day fasting on obesity and cardiometabolic risk: A systematic review and meta-analysis [Internet]. Metabolism: Clinical and Experimental. W.B. Saunders; 2020 [cited 2021 Jun 24]. Available from:

5. Fujikake N, Shin M, Shimizu S. Association between autophagy and neurodegenerative diseases [Internet]. Frontiers in Neuroscience. Frontiers Media S.A.; 2018 [cited 2021 Jun 9]. p. 255. Available from: /pmc/articles/PMC5972210/

6. Gao F, Chen J, Zhu H. A potential strategy for treating atherosclerosis: Improving endothelial function via amp-activated protein kinase. Science China Life Sciences. Science in China Press; 2018. p. 1024–9. 

7. Martinez-Lopez N, Tarabra E, Toledo M, Garcia-Macia M, Sahu S, Coletto L, Batista-Gonzalez A, Barzilai N, Pessin JE, Schwartz GJ, et al. System-wide Benefits of Intermeal Fasting by Autophagy. Cell Metab [Internet]. Cell Press; 2017 [cited 2021 Jun 9];26:856-871.e5. Available from: /pmc/articles/PMC5718973/

8. Barnosky AR, Hoddy KK, Unterman TG, Varady KA. Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: A review of human findings [Internet]. Translational Research. Mosby Inc.; 2014 [cited 2021 Jun 24]. p. 302–11. Available from:

9. Gabel K, Kroeger CM, Trepanowski JF, Hoddy KK, Cienfuegos S, Kalam F, Varady KA. Differential Effects of Alternate-Day Fasting Versus Daily Calorie Restriction on Insulin Resistance. Obesity [Internet]. Blackwell Publishing Inc.; 2019 [cited 2021 Jun 24];27:1443–50. Available from: /pmc/articles/PMC7138754/

10. Zouhal H, Saeidi A, Salhi A, Li H, Essop MF, Laher I, Rhibi F, Amani-Shalamzari S, Ben Abderrahman A. <p>Exercise Training and Fasting: Current Insights</p>. Open Access J Sport Med [Internet]. Informa UK Limited; 2020 [cited 2021 Jun 24];Volume 11:1–28. Available from: /pmc/articles/PMC6983467/

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