Prolonged Fasting: 5 Amazing Health Benefits Plus 3 Side Effects

Medically Reviewed by Ana Reisdorf MS, RD on January 13, 2020.

Unlike other forms of intermittent fasting, such as the 5:2 fast, 16-hour fasts, and 24-hour fasts, little is known about prolonged fasting. 

It may be just because only a few people are doing it. (Learn more about the types of Intermittent Fasting here). Or, maybe it is so hard that many people give up the idea of trying it when they hear the duration of fasting. 

Intermittent fasting (IF) has become increasingly popular among weight-watchers, bodybuilders, and celebrities. And, why not? After all, strong evidence shows alternating between feeding and fasting periods has a myriad of benefits. 

Are you ready to work your way up from the regular 16-hours fast to prolonged fasting?
If yes, please read this article until the end. This will help you make the best decision and optimize the benefits. 

What is Prolonged Fasting? Learn the Basics

Ever googled “prolonged fasting vs. intermittent fasting”? The answer is prolonged fasting is essentially the “hardcore” version of regular intermittent fasting methods. 

In simple terms, prolonged fasting is eating nothing for 2 days in a row. However, you may drink zero-calorie fluids during the fasting days. These include water, unsweetened tea, and black coffee. 

Drinking plenty of water during the fasting days is critical to preventing dehydration and its associated symptoms. Some people prefer to drink water only during this period. This is known as prolonged water fasting.  

Likewise, when you break the fast, make sure to gradually increase the amount of food you eat. Simply put, do not overeat once the fasting period is over. This will help prevent digestive issues like nausea, bloating, and upset stomach. 

On the feeding days, stick to your usual eating habits but do not overfeed. 

You may consider doing prolonged fasting once or twice every month depending on your health and preference. 

Just as fasting is not for everyone, prolonged fasting is not suitable for newbies.
Typically, this intermittent fasting method is ideal for those who have already practiced the 16-hour fast, alternate day fast (ADF), or 5:2 diet.  

5 Science-Backed Benefits of Prolonged Fasting

Here, we look at the science behind prolonged fasting benefits.  

1. Prolonged Fasting Could be the “Fountain of Youth”

Animal studies have shown that prolonged fasting increases lifespan and improves health. 

Likewise, a recent study shows encouraging prolonged fasting results in humans as well. 

According to researchers at the Okinawa Institute of Science and Technology Graduate (OIST) University, fasting for more than 50 hours “revs up metabolism, increases antioxidant levels, and helps reverse some effects of aging.

Cellular aging is a natural process characterized by two key features:

  1. Increased cellular damage. 
  2. Decreased efficiency of protective mechanisms such as autophagy. Further Reading: What is Autophagy?

As a result, the cells gradually lose their functional ability and eventually die. 

Studies have shown that prolonged fasting boosts autophagy and reduces DNA damage, both of which can delay aging and improve health. 

2. Prolonged Fasting Reduces Oxidative Stress

Oxidative stress increases when the body’s antioxidant mechanisms fail to counteract the effects of “potentially harmful” chemical species. These chemical species are collectively known as reactive oxygen and nitrogen species (RONS). 

Increased oxidative stress has been linked to accelerated aging and a higher risk of many chronic diseases. For example, heart disease, kidney disease, cognitive decline, and cancer. 

Prolonged fasting reduces oxidative stress in two ways. 

First, it increases the levels of RONS-fighting antioxidant enzymes in the body. Second, it limits damages to the mitochondria, the cells’ main source of energy. Mitochondrial damages are the hallmarks of almost every chronic disease. 

3. It May Help People with Multiple Sclerosis

Multiple sclerosis (MS) is a disease of the nervous system. MS slows down or completely blocks communication between your body and the brain. 

Typical symptoms include:

  • Vision problems
  • Muscle weakness
  • Coordination and balance problems
  • Numbness and prickling
  • Memory problems 

More than one million Americans have MS. Sadly, it has no known cure and treatments are only supportive.  

The effect of prolonged fasting on multiple sclerosis is a new arena of study and no conclusive results are available. 

That said, there have been a few studies on the effects of intermittent fasting on MS. For example, one study found that intermittent fasting might help relieve MS symptoms by reducing inflammation and damages to the nerve cells. 

Interestingly, an earlier study suggests that prolonged fasting has no negative effects on people with MS. 

Based on the findings, researchers believe that prolonged fasting could be an add-on to currently available MS treatments. 

4. It Could be a New Addition to Your “Weight Loss” Arsenal 

Undoubtedly, intermittent fasting is a well-established approach to healthy weight loss. Interestingly, emerging research shows prolonged fasting could be your new companion in the weight-loss journey. 

Estimates suggest that fasting for 2 days once or twice a month can cause a net calorie deficit of around 8,000 calories. This is equivalent to a loss of more than 2 pounds of fat each month. 

Likewise, a 48-hour fast can increase your metabolic rate and energy expenditure. This means you may be able to lose weight even when you are resting. 

Another way a 48-hour fast can aid weight loss is by depleting the glycogen (stored carbs) stores in your liver and muscles. Typically, in prolonged fasting, it takes more than 24 hours for glycogen in your liver to be depleted.  

5. It Improves Insulin Sensitivity and Helps Maintain Healthy Blood Sugar Levels 

Insulin sensitivity is the ability of cells to use available insulin. 

Insulin is a hormone produced by the pancreas. It helps transport sugar molecules from the bloodstream to the cells.
Decreased insulin sensitivity causes elevated blood sugar levels, which may lead to diabetes.
When you do not eat anything for more than 24 hours, your body starts using glycogen and eventually fat as a source of energy. This can lead to better blood glucose control. 

In people with type II diabetes, fasting for 24 to 72 hours causes a 20 percent drop in blood sugar levels.

Prolonged Fasting Side Effects: 3 Things You Should Know 

Prolonged fasting is not free from potential downsides. 

Before you decide to go hungry for days, make sure to learn the side effects to lower your risk of complications. Common side effects include: 

1. Severe hunger and dizziness

Well, you are going to be very very hungry when you do not eat anything for two days. 

Hunger is not the only side effect of prolonged fasting. You may become dizzy, insomniac, and weak as well. 

Some people say that these symptoms go away on their own once your body adapts to prolonged periods of abstinence from food. However, your experience may be different. 

Thus, it is important to first try easier forms of intermittent fasting such as 16-hour fasts, 24-hour fasts, and alternate-day fasting. 

2. Dehydration and Electrolyte Imbalance

If you do not drink plenty of fluid during the fasting period, your risk of dehydration increases significantly. Likewise, some people may have an electrolyte imbalance. 

Electrolytes are salts that help maintain several functions in the body. Common electrolytes include sodium, potassium, chloride, and calcium. 

Both dehydration and electrolyte imbalance can be potentially life-threatening if you do not seek prompt care. 

In fact, in one study, out of 768 people who fasted for more than 48 hours, one person developed the symptoms of dehydration on the third day of fasting. Notably, the person had to be admitted to an emergency facility. 

In the same study, another person developed hyponatremia. Hyponatremia is a condition in which a person has dangerously low blood levels of sodium. The person stayed in the emergency facility for four days before a full recovery. 

3. Increased Anger

You will likely be hangry (hungry and then angry) while doing prolonged fasting. 

While it is common knowledge that hunger triggers anger, a recent study suggests that anger could be the only mood state triggered by hunger. 

In the study, fasting for 48 hours significantly increased anger in amateur weight lifters. However, researchers observed no significant changes in other mood states such as depression confusion and vigor. 

You would not want to yell at your kids or fly off the handle at the drop of a hat, just because you have not eaten anything for 2 days! 

So, make sure to learn anger management before starting prolonged fasting. 

How to Do Prolonged Fasting for Best Results?

With proper strategies, you can not only optimize the benefits but also prevent side effects.

  • Stay hydrated all the time. Plain water is the best option. However, you may go for flavored water to serve your taste buds. 
  • Drink unsweetened tea or coffee to deal with hunger pangs. 
  • Watch a movie, read a book, or indulge in some low-intensity activity to keep your mind occupied. Remember hunger is often in the mind, not in the stomach. 
  • If you already have anger management issues, learn strategies to stay calm while fasting. It could be as simple as a few minutes of deep breathing. 
  • If you feel extremely uneasy during the fasting period, remember you can quit anytime and start afresh. 
  • Consult your doctor if you have any disease or take medications.  

Bottom Line

So, should You Try Prolonged Fasting?

You could consider engaging in prolonged fasting but there is a catch. You cannot expect to run if you have not yet started to walk.
Start with short-duration intermittent fasting methods and see how your body responds. Once you become confident of it, you can work your up to prolonged fasting.