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

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

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

Another possible avenue for promoting weight loss and improving certain markets of 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. 

Another option is to fast one day per week. Some people find success with 36 hour fasting, one time per week.

In this article, we will discuss 36 hour fast benefits and if doing a 36 hour fast once a week can help you lose weight.

More specifically, we will cover: 

  • How Do You Do a 36 Hour Fast?
  • 14 Benefits of 36 Hour Fasting Once a Week
  • Downsides and Risks Of 36 Hour Fasting Once a Week

Let’s jump in!

An alarm clock with the word fasting in front of it.

How Do You Do a 36-Hour Fast?

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 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 3 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.

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.

14 Benefits of 36 Hour Fasting Once a Week

One of the potential 36 hour fast benefits is weight loss, and indeed the prospect of losing weight is one of the primary reasons that people try any sort of 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 weight with no serious adverse events. 

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: altering your circadian biology, modifying your gut microbiome, and you shift modifiable lifestyle behaviors such as your sleep patterns and energy intake.

In terms of 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.

A note book that says intermittent fasting, an alarm clock, a plate and silverwear.

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.

Additionally, doing 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 end up creating a substantial caloric deficit because you will continue to burn calories even though you’re not replacing them.

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.

A person with a measuring tape around their waist showing weight loss from 36 hour fasting.

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:

  • 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 dying cells.
  • Reducing inflammation, which is a key driver underlying many chronic diseases such as obesity, metabolic syndrome, type 2 diabetes, heart disease, and certain cancers.
  • Reducing the risk of various diseases, such as diabetes, certain cancers, and neurodegenerative diseases, such as Alzheimer’s disease.

As can be seen, there are quite a few potential health benefits of 36 hour fasting once a week.

The words reduce risk.

Downsides and Risks Of 36 Hour Fasting Once a Week

Although there can be quite a few potential health benefits of doing a 36 hour fast once a week, there are also some possible downsides and contraindications.

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 downsides of fasting is that it can lead to compensatory overeating or binging after the fasting period. 

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 restricting, wherein people feel like they have the liberty to eat a lot more because they were so disciplined 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 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 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.

Related: BMI Healthy Weight Calculator

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.

Although 36 hour fasting once a week isn’t necessarily safe or effective for everyone, it can be a potential way to 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 would like to start out with a shorter fast, try a 24-hour fast with our guide here.

Empty plates with silverware on either side.
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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