48 Vs 72 Hour Fasting: Comparing The Effects + Benefits

When deciding to take on a fast, one of the first decisions you will need to make is the length of the fast. One day, two, three?

If you are going back and forth between a 2 or 3 day fast, you may be wondering which is better, a 48 hour water fast or a 72 hour water fast?

What are the physiological differences in the benefits and stages of a 48 vs 72 hour water fast? Are certain benefits of fasting only realized with a 72-hour vs 48-hour water fast?

In this article, we will discuss the benefits of a 48 hour water fast and a 72 hour water fast and compare and contrast the differences in doing a 48 vs 72 hour fast to help you determine whether it is better for you.

We will cover the following: 

  • 48 Vs 72 Hour Fasting Compared
  • 48 vs 72 Hour Fasting: Physiological Differences
  • 48 vs 72 Hour Fasting: Experience 
  • 48 vs 72 Hour Fasting: Health Risks

Let’s jump in!

A person smiling holding up a sign that says fasting with empty plates in front of him.

48 Vs 72 Hour Fasting Compared

There are a couple of different things to consider when comparing the differences between a 48 vs 72 hour fast. 

Namely, there are physiological differences between a 48 water fast vs 72 hour water fast because of the extended duration of the 72 hour fast. 

Additionally, there are practical/logistical differences between doing a 2 vs 3 day water fast as well as potential health risks and physical symptoms that will vary whether you are water fasting for 48 hours or 72 hours.

Let’s look at the main differences between a 48 vs 72 hour fast:

48 vs 72 Hour Fasting: Physiological Differences

When you are trying to compare the differences between doing a 2 or 3 day fast, it helps to look at the stages of fasting to see what sorts of physiological changes occur after 48-hours.

A clock made from a plate, fork and knife.

Once you have been fasting for 48 hours, certain metabolic and physiological effects have taken place.

First, your body will shift into a state of ketosis around 18 hours after you have begun fasting. This occurs because your glycogen stores have been depleted, and the body has to shift to burning fat for fuel. 

Then, after about 24 hours of fasting, the process of autophagy is said to begin.

Autophagy is essentially a cell cleanup and debridement process where dead and damaged cells and cell fragments are removed from wherever they are “gunking up“ the tissue or region of the body where they are located.

Viable cell components and proteins can be recycled and reassembled for new cells or to repair damaged cells, while damaged and misfolded proteins are destroyed.

After a 48 hour fast, your body will experience a significant increase in the level of human growth (HGH)—which may rise to upwards of five times your normal HGH concentration. This hormone can help rebuild and repair cells and tissues. 

Pouring a glass of water.

If you do a 48 hour vs 72 hour fast, the physiological benefits of fasting will mostly end here.

Over the next 24 hours, additional prolonged fasting benefits include a significant drop in insulin levels, which typically occurs after fasting 60 hours or more, and the destruction and regeneration of old immune cells for new immune cells. 

This can improve the health and function of your immune system.

The other effects of fasting that occur earlier on in the process will extend throughout the duration of your fast for the most part. 

This means that you will be in ketosis longer, have continual autophagy occurring, and see a continuation of higher levels of human growth hormone when doing a 72 vs 48 hour fast.

48 vs 72 Hour Fasting: Experience 

Aside from the physiological differences that occur with a 48 vs 72 hour fast, you also need to consider the practical implications and difficulty incurred by each.

48 Vs 72 Hour Fasting: Comparing The Effects + Benefits 1

Conceivably, if you are trying to decide whether to do a 48 hour water fast or 72 hour water fast, you have already done at least one 24 hour water fast if not a 2 or 3 day water fast in the past.

Therefore, you likely recall that prolonged fasting is difficult.

It is physically uncomfortable to deny yourself food when your body sends signals to eat through an increase in appetite hormones.

Abstaining from taking in any caloric foods or drinks can cause a dip in energy, irritability, headaches, fatigue, difficulty concentrating, food cravings and a ravenous appetite, difficulty exercising, and sleep disturbances, among other symptoms.

When you are doing a shorter water fast, it’s easier to see the finish line and talk yourself through the challenging moments and uncomfortable physical and mental sensations of fasting.

For some people, extending the duration of a water fast by doing a 72 hour fast gets exponentially harder in that the additional 24 hours can feel like it stretches for days.

An empty plate with a clock next to it.

For other people, once you are doing prolonged fasting, your body and mind adjust to the discomfort of hunger and the lack of taking in calories, and it actually doesn’t feel appreciably more difficult to do a 3 vs 2 day fasting protocol.

If you have experience trying fasting in the past, you likely have some gauge of how your body and mind respond to fasting.

If you fall into the camp where it is quite uncomfortable and increasingly more challenging to do a prolonged fasting protocol, it may be better to stick with a 48 vs 72 hour water fasting protocol

This will save you from the agony and real struggle of fasting while still giving you most of the same benefits.

On the other hand, if you find that your body actually seems to thrive while you are fasting, or at least tolerates the lack of energy intake in a workable way, you may prefer to do a 72 vs 48 hour fast to maximize the benefits of extended fasting.

To this end, in addition to the physical difficulties of fasting for two or three days, another thing to consider is the feasibility of fitting in a fast with your schedule. 

48 Vs 72 Hour Fasting: Comparing The Effects + Benefits 2

Many people don’t feel very well during prolonged fasting. If you are doing a 48 vs 72 hour fast, you can plan your 2-day fast for the weekend when you don’t have to interact with other people and expect high productivity from yourself at your job. 

However, once you add that extra 24 hour fasting extension by going to a 72 hour fast, it can be much harder to navigate the logistics of finding time in your schedule with work and other obligations.

Plus, if you have a partner who isn’t fasting (or you have children who should not be fasting), or you simply have a social life that normally has you going out to eat or drink with others, it is more difficult to manage the isolation and dietary incompatibilities with a 72 hour fast.

Because there aren’t necessarily a ton of additional health benefits to gain by fasting 72 hours vs fasting 48 hours, plenty of people find that decreasing any additional burden or challenge from a logistical or social standpoint makes the shorter fast a better fit.

A person drinking a glass of water.

48 vs 72 Hour Fasting: Health Risks

The last thing to consider when deciding whether you should do a 48 vs 72 hour fast is the potential health risks that increase when you extend your fast for another 24 hours.

You should always seek medical guidance before you try any prolonged fasting protocol beyond just a basic intermittent fasting diet with a restricted eating window every day.

There are certain health conditions and medications that make prolonged fasting contraindicated, whether or not you are choosing to do a 2-day fast or a 3-day fast.

That said, even if you get medical clearance from your doctor, the risks associated with fasting for an extended period of time increase the longer that you fast.

For example, prolonged fasting can result in adverse health and metabolic changes such as dehydration, a loss of lean muscle mass, hyperuricemia, hyponatremia, protein-sparing, sodium and potassium-sparing, decreased serum calcium and magnesium levels, and acidic urine.

Ultimately, deciding whether it is better to do a 48 or 72 hour water fast for your own personal circumstances is a matter of having a thorough understanding of these differences and weighing the pros and cons of both relative to the needs in your own life.

Looking for some guidance on your 48 hour water fast? Check out our guide to 2 day water fasting here.

A person drinking a bottle of water.
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.

3 thoughts on “48 Vs 72 Hour Fasting: Comparing The Effects + Benefits”

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.