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36 Hour Fasting: The Top Benefits Of A 36 Hour Fast Once A Week

Our nutrition coach gives us her expert advice on prolonged fasting.

There are many ways to manipulate your diet to improve your health and help you lose weight potentially.

You can follow a popular diet that promises weight loss by eliminating certain foods or food groups, such as carbohydrates on Keto. Or you can focus on diet quality and minimizing processed foods with the Mediterranean or DASH diet.

Another possible avenue for promoting weight loss and improving certain health markets like heart health is fasting.

Some people try intermittent fasting diets that restrict their daily eating window to a certain number of hours, usually by prolonging the overnight fast throughout the morning. 

Other options include alternate-day fasting, the OMAD diet, or fasting one day per week. Some people find success with 36 hours of fasting, once a week.

This article will discuss 36 hour fasting benefits and whether implementing this fasting method once a week into your lifestyle can help you lose weight.

Let’s jump in!

36 hour countdown clock on a grey background with a breakfast bowl and avocado and fried egg toast.
Credit: Marathon Handbook Staff

What Is The 36 Hour Fast Protocol?

A 36 hour fast, also called a 36 hour water fast, involves abstaining from all food and calorie-containing beverages for 36 hours.

Most people accomplish this by stopping eating in the evening of one day, say at 7:00 PM after dinner, fasting overnight and all through the next day, through the following night until 7:00 AM the following morning. 

The 36 hour fast would then be broken with that breakfast. You can adjust the hours in either direction, but this is the typical way that people approach a 36 hour fast once a week.

During the 36 hour fasting period, you can have plenty of water, plain herbal tea with no added sweeteners, seltzer or club soda, or black coffee. 

Adding electrolytes to your water is advisable to prevent electrolyte imbalances and dehydration. A good option for a non-caloric electrolyte powder is Ultima.

Black coffee is also permissible because one cup (240 ml) of black coffee contains approximately three calories and just trace amounts of protein, fat, and minerals. 

Consequently, the nutrient content is so low that even a couple of cups of black coffee won’t really induce any metabolic changes or take you out of a fasted state.1van Dam, R. M., Pasman, W. J., & Verhoef, P. (2004). Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentrations: Randomized controlled trials in healthy volunteers. Diabetes Care27(12), 2990–2992. https://doi.org/10.2337/diacare.27.12.2990

‌However, for strict fasting, you should not add caloric sweeteners or cream, MCT oil, milk, or grass-fed butter.

A cup of black coffee with coffee beans on the side of the saucer.

What Are The Potential Health Benefits And Risks Of A 36-Hour Fast?

One of the potential 36 hour fast benefits is weight loss, and the prospect of losing weight is one of the primary reasons people try any sort of time-restricted fasting diet.

A review of 27 intermittent fasting dietary interventions found that all 27 studies resulted in weight loss of 0.8% to 13.0% of the starting body weight with no serious adverse events.2Welton, S., Minty, R., O’Driscoll, T., Willms, H., Poirier, D., Madden, S., & Kelly, L. (2020). Intermittent fasting and weight loss. Canadian Family Physician66(2), 117–125. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7021351/

According to research, periodic fasting, such as doing a 36 hour water fast once a week, alters the metabolism and supports weight loss through three primary ways.

Fasting alters your circadian biology, modifies your gut microbiome, and shifts modifiable lifestyle behaviors such as your sleep patterns and energy intake.

Regarding altering your circadian biology, fasting 36 hours usually involves doing a full 24-hour fast and then extending that fast through the next night, finally breaking the fast the following morning.

This confines your eating window in such a way that you won’t be eating outside of the normal daylight hours.

Eating at abnormal hours disturbs the 24-hour circadian rhythm in our body, which disturbs the natural cycles that affect our biology and behavior, governing things like wakefulness and sleep, metabolism and energetics, and hormonal secretion patterns.

Studies have shown that late-night eating, or eating outside of a typical daylight window, is associated with higher insulin secretion and glucose levels, which can result in weight gain.3Scheer, F. A. J. L., Hilton, M. F., Mantzoros, C. S., & Shea, S. A. (2009). Adverse metabolic and cardiovascular consequences of circadian misalignment. Proceedings of the National Academy of Sciences106(11), 4453–4458. https://doi.org/10.1073/pnas.0808180106

Additionally, doing prolonged fasting of a 36 hour fast once a week can promote weight loss and favorable improvements in body composition because it can generate a significant caloric deficit

By skipping an entire day and a half of eating, you will create a substantial caloric deficit because you will continue to burn calories even though you’re not replacing them with calorie intake.

With that said, the effectiveness of a 36 hour fast once a week for weight loss will depend on your overall caloric balance for the week; if you are able to sustain a caloric deficit from fasting without rebound compensatory eating the subsequent days, then you will lose weight.

In addition to the potential weight loss benefits of doing 36 hour fasting once a week, the health benefits of fasting for 36 hours once a week can include the following:

Potential Benefits Of A 36 Hour Fast

  • Reducing the risk of cardiovascular disease and coronary artery disease 
  • Reducing the risk of metabolic syndrome.4Horne, B. D., Muhlestein, J. B., Lappé, D. L., May, H. T., Carlquist, J. F., Galenko, O., Brunisholz, K. D., & Anderson, J. L. (2013). Randomized cross-over trial of short-term water-only fasting: Metabolic and cardiovascular consequences. Nutrition, Metabolism and Cardiovascular Diseases23(11), 1050–1057. https://doi.org/10.1016/j.numecd.2012.09.007
  • Helping your body fight cancer.5Di Biase, S., Lee, C., Brandhorst, S., Manes, B., Buono, R., Cheng, C.-W., Cacciottolo, M., Martin-Montalvo, A., de Cabo, R., Wei, M., Morgan, T. E., & Longo, V. D. (2016). Fasting-Mimicking Diet Reduces HO-1 to Promote T Cell-Mediated Tumor Cytotoxicity. Cancer Cell30(1), 136–146. https://doi.org/10.1016/j.ccell.2016.06.005
  • Reducing the risk of heart attack and stroke.6MATTSON, M., & WAN, R. (2005). Beneficial effects of intermittent fasting and caloric restriction on the cardiovascular and cerebrovascular systems. The Journal of Nutritional Biochemistry16(3), 129–137. https://doi.org/10.1016/j.jnutbio.2004.12.007
  • Increasing the production of human growth hormone (HGH).7Home Page: The American Journal of Clinical Nutrition. (n.d.). Ajcn.nutrition.org. https://ajcn.nutrition.org/
  • Promoting optimal cellular health and autophagy, which is a cellular clean-up process whereby the healthy cells get rid of cellular waste products and dead and damaged cells.8Bagherniya, M., Butler, A. E., Barreto, G. E., & Sahebkar, A. (2018). The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Research Reviews47, 183–197. https://doi.org/10.1016/j.arr.2018.08.004
  • Helping the body defend your body from oxidative stress, which is damage that occurs from free radicals and reactive species.9Cienfuegos, S., Gabel, K., Kalam, F., Ezpeleta, M., Wiseman, E., Pavlou, V., Lin, S., Oliveira, M. L., & Varady, K. A. (2020). Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. Cell Metabolism32(3), 366-378.e3. https://doi.org/10.1016/j.cmet.2020.06.018
  • Reducing inflammation, a key driver underlying many chronic diseases such as obesity, metabolic syndrome, type 2 diabetes, heart disease, and certain cancers.10Jordan, S., Tung, N., Casanova-Acebes, M., Chang, C., Cantoni, C., Zhang, D., Wirtz, T. H., Naik, S., Rose, S. A., Brocker, C. N., Gainullina, A., Hornburg, D., Horng, S., Maier, B. B., Cravedi, P., LeRoith, D., Gonzalez, F. J., Meissner, F., Ochando, J., & Rahman, A. (2019). Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool. Cell178(5), 1102-1114.e17. https://doi.org/10.1016/j.cell.2019.07.050
  • Stimulating neurogenesis (the growth of new neurons).11Baik, S.-H., Rajeev, V., Fann, D. Y.-W., Jo, D.-G., & Arumugam, T. V. (2020). Intermittent fasting increases adult hippocampal neurogenesis. Brain and Behavior10(1), e01444. https://doi.org/10.1002/brb3.1444
  • Increasing longevity.12Goodrick, C. L., Ingram, D. K., Reynolds, M. A., Freeman, J. R., & Cider, N. L. (1982). Effects of intermittent feeding upon growth and life span in rats. Gerontology28(4), 233–241. https://doi.org/10.1159/000212538
  • Reducing insulin levels, which can reduce the risk of insulin resistance while also supporting body fat loss.13Hoddy, K. K., Gibbons, C., Kroeger, C. M., Trepanowski, J. F., Barnosky, A., Bhutani, S., Gabel, K., Finlayson, G., & Varady, K. A. (2016). Changes in hunger and fullness in relation to gut peptides before and after 8 weeks of alternate day fasting. Clinical Nutrition35(6), 1380–1385. https://doi.org/10.1016/j.clnu.2016.03.011
  • Increasing metabolic rate.14Teruya, T., Chaleckis, R., Takada, J., Yanagida, M., & Kondoh, H. (2019). Diverse metabolic reactions activated during 58-hr fasting are revealed by non-targeted metabolomic analysis of human blood. Scientific Reports9(1). https://doi.org/10.1038/s41598-018-36674-9
  • Reducing the risk of various diseases, such as diabetes, certain cancers, and neurodegenerative diseases, such as Alzheimer’s disease

Downsides and Risks Of 36 Hour Fasting Once a Week

Although there can be many potential health benefits of doing a 36 hour fast once a week, there are also some possible downsides and contraindications to this extended fasting.

Fasting for 36 hours isn’t always the most effective weight loss strategy for everyone, let alone the healthiest, depending on your mindset around food, medical history, and physiological and psychological needs.

Some fasting experts believe that one of the potential risks or side effects of fasting is that it can lead to compensatory overeating or binging after the fasting period.15Collier, R. (2013). Intermittent fasting: the science of going without. Canadian Medical Association Journal185(9), E363–E364. https://doi.org/10.1503/cmaj.109-4451

‌Post-fasting binging can be due to the biological urge to secure more calories and compensate for the energy deficit.

A plate with a fork and spoon on it.

There can also be an emotional/behavioral response to extreme restriction, wherein people feel like they have the liberty to eat a lot more because they were so disciplined in sticking to a 36 hour fast and can now afford to ingest a lot more calories.

Either way, overeating after a fast can all but negate potential weight loss results if the overeating reverses the caloric deficit generated by the fast.

Additionally, even when the effects on fat loss are ignored, binge eating has negative health effects, as it often causes rapid and significant increases in blood sugar levels and blood pressure.

Aside from the risk of compensatory binge eating, fasting for 36 hours once a week is also not usually a good diet for those trying to improve athletic performance or do intense exercise training. 

Endurance exercise and high-intensity workouts can be very difficult (and potentially unsafe) to perform in a fasted state because your body will not have ample glycogen to fuel your muscles.

On the other hand, if you wait until after your eating window has ended for the day to exercise, you won’t be able to refuel with carbs and protein after the workout.

A cup of herbal tea.

This can compromise your recovery and minimize the potential gains in muscular size and strength by impeding the process of muscle protein synthesis and glycogen replacement.

Anyone interested in trying intermittent fasting should consult their physician, particularly those with the following conditions:

Trying to fast 36 hours once a week is unsafe for individuals who are pregnant or breastfeeding, are under the age of 20 (because they are still growing), are underweight (BMI <18.5 kg/m2), have an active eating disorder or have advanced kidney or heart disease.

Additionally, people who take prescription medications or who have electrolyte imbalances, hypotension, or type I or type II diabetes should consult their healthcare provider before trying any type of fasting.

Is Fasting For 36 Hours Good For You?

Although 36 hour fasting once a week isn’t necessarily safe or effective for everyone, it can potentially boost health and support weight loss goals for others.

If you are interested in trying 36-hour fasting, speak with your doctor for personalized recommendations.

If you want to start with a shorter fast, try a 24-hour fast with our guide here.

References

  • 1
    van Dam, R. M., Pasman, W. J., & Verhoef, P. (2004). Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentrations: Randomized controlled trials in healthy volunteers. Diabetes Care27(12), 2990–2992. https://doi.org/10.2337/diacare.27.12.2990
  • 2
    Welton, S., Minty, R., O’Driscoll, T., Willms, H., Poirier, D., Madden, S., & Kelly, L. (2020). Intermittent fasting and weight loss. Canadian Family Physician66(2), 117–125. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7021351/
  • 3
    Scheer, F. A. J. L., Hilton, M. F., Mantzoros, C. S., & Shea, S. A. (2009). Adverse metabolic and cardiovascular consequences of circadian misalignment. Proceedings of the National Academy of Sciences106(11), 4453–4458. https://doi.org/10.1073/pnas.0808180106
  • 4
    Horne, B. D., Muhlestein, J. B., Lappé, D. L., May, H. T., Carlquist, J. F., Galenko, O., Brunisholz, K. D., & Anderson, J. L. (2013). Randomized cross-over trial of short-term water-only fasting: Metabolic and cardiovascular consequences. Nutrition, Metabolism and Cardiovascular Diseases23(11), 1050–1057. https://doi.org/10.1016/j.numecd.2012.09.007
  • 5
    Di Biase, S., Lee, C., Brandhorst, S., Manes, B., Buono, R., Cheng, C.-W., Cacciottolo, M., Martin-Montalvo, A., de Cabo, R., Wei, M., Morgan, T. E., & Longo, V. D. (2016). Fasting-Mimicking Diet Reduces HO-1 to Promote T Cell-Mediated Tumor Cytotoxicity. Cancer Cell30(1), 136–146. https://doi.org/10.1016/j.ccell.2016.06.005
  • 6
    MATTSON, M., & WAN, R. (2005). Beneficial effects of intermittent fasting and caloric restriction on the cardiovascular and cerebrovascular systems. The Journal of Nutritional Biochemistry16(3), 129–137. https://doi.org/10.1016/j.jnutbio.2004.12.007
  • 7
    Home Page: The American Journal of Clinical Nutrition. (n.d.). Ajcn.nutrition.org. https://ajcn.nutrition.org/
  • 8
    Bagherniya, M., Butler, A. E., Barreto, G. E., & Sahebkar, A. (2018). The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Research Reviews47, 183–197. https://doi.org/10.1016/j.arr.2018.08.004
  • 9
    Cienfuegos, S., Gabel, K., Kalam, F., Ezpeleta, M., Wiseman, E., Pavlou, V., Lin, S., Oliveira, M. L., & Varady, K. A. (2020). Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. Cell Metabolism32(3), 366-378.e3. https://doi.org/10.1016/j.cmet.2020.06.018
  • 10
    Jordan, S., Tung, N., Casanova-Acebes, M., Chang, C., Cantoni, C., Zhang, D., Wirtz, T. H., Naik, S., Rose, S. A., Brocker, C. N., Gainullina, A., Hornburg, D., Horng, S., Maier, B. B., Cravedi, P., LeRoith, D., Gonzalez, F. J., Meissner, F., Ochando, J., & Rahman, A. (2019). Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool. Cell178(5), 1102-1114.e17. https://doi.org/10.1016/j.cell.2019.07.050
  • 11
    Baik, S.-H., Rajeev, V., Fann, D. Y.-W., Jo, D.-G., & Arumugam, T. V. (2020). Intermittent fasting increases adult hippocampal neurogenesis. Brain and Behavior10(1), e01444. https://doi.org/10.1002/brb3.1444
  • 12
    Goodrick, C. L., Ingram, D. K., Reynolds, M. A., Freeman, J. R., & Cider, N. L. (1982). Effects of intermittent feeding upon growth and life span in rats. Gerontology28(4), 233–241. https://doi.org/10.1159/000212538
  • 13
    Hoddy, K. K., Gibbons, C., Kroeger, C. M., Trepanowski, J. F., Barnosky, A., Bhutani, S., Gabel, K., Finlayson, G., & Varady, K. A. (2016). Changes in hunger and fullness in relation to gut peptides before and after 8 weeks of alternate day fasting. Clinical Nutrition35(6), 1380–1385. https://doi.org/10.1016/j.clnu.2016.03.011
  • 14
    Teruya, T., Chaleckis, R., Takada, J., Yanagida, M., & Kondoh, H. (2019). Diverse metabolic reactions activated during 58-hr fasting are revealed by non-targeted metabolomic analysis of human blood. Scientific Reports9(1). https://doi.org/10.1038/s41598-018-36674-9
  • 15
    Collier, R. (2013). Intermittent fasting: the science of going without. Canadian Medical Association Journal185(9), E363–E364. https://doi.org/10.1503/cmaj.109-4451
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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