The 6 Stages Of Water Fasting: The Complete Water Fasting Timeline

Water fasting involves abstaining from all food and caloric beverages for an extended period of time.

But, what are the stages of water fasting? What should you expect for a water fasting timeline in terms of the various water fasting stages your body will go through for longer water fasts?

In this article, we will discuss what happens to your body when you take on a water fast and provide a general overview of the water fasting timeline with the different stages of water fasting.

Let’s dive in! 

A person sitting at a kitchen table with a glass of water and a fork.

What Are the Stages of Water Fasting?

Although each of us has somewhat of a unique biochemistry such that fasting can affect the exact water fasting timeline your body goes through, there are general stages of water fasting that we all go through.

Because water fasting involves a cessation of consuming any calories, water fasting places the body into an energy deficit once you have been fasting for a certain number of hours.

Due to the fact that there is low energy availability because you’re not consuming calories while fasting, your body undergoes various changes to your metabolic and hormonal balance during extended fasting protocols.

There are several reported phases of fasting that your body goes through during a prolonged water fast, as described by the general water fasting stages outlined below:

A person drinking a glass of water.

Stage 1: 12 Hours Of Water Fasting

It takes about 12 hours of fasting before any appreciable metabolic effects of fasting take hold. This is because your body still has available calories/fuel from your previous meal before you started fasting.

After about 12 hours of fasting, your body will start to run out of stored muscle and liver glycogen.

Glycogen is the storage form of carbohydrates and a preferred fuel source for certain cells of the body at all times, such as the brain and red blood cells, as well as the preferred fuel source for the muscles during high-intensity exercise.

Once glycogen has been depleted, the body will shift into a state of ketosis. Ketosis involves breaking down and oxidizing fat for energy instead of carbohydrates.

Physically, you will not necessarily feel a detectable difference in how your body feels when ketosis first kicks in unless you are trying to do vigorous physical activity. 

With exercise, if you are not a “fat-adapted athlete,” meaning that your body is not accustomed to readily burning fat for fuel at a high intensity, you may feel sluggish and tired during your workouts.

This is because it takes longer for the muscles to burn fat to make ATP compared to carbohydrates.

You will also probably start feeling pretty hungry and may experience low blood sugar symptoms such as lethargy, difficulty concentrating, irritability, and food cravings.

A dial pointing to ketones.

Stage 2: 18 Hours Of Water Fasting

Although the onset of ketosis will occur during the first stage of water fasting after about 12 hours with no caloric intake, it’s not until about 18 hours that most people are truly in a state of ketosis.

Here, your body is primarily burning fat for fuel because glycogen stores are almost entirely depleted.

The body stores about 80 grams of glycogen in the liver, a very small amount of glycogen in the brain, about 4 grams of glucose in the bloodstream, and upwards of 500 grams of glycogen in the skeletal muscles, depending on your body size, muscle mass, sex, and training status.

Due to these many variables, they can be a fairly wide range in terms of the total number of grams of glycogen stored in the body, but researchers suggest that a good ballpark average for an adult is 600 grams of glycogen.

Because each gram of glycogen can supply approximately four calories worth of energy, this research suggests that we have about 2400 calories worth of energy stored as glycogen. 

A woman smiling with a glass of water.

This is slightly higher than the total number of calories in glycogen storage, according to the Academy of Nutrition and Dietetics, which estimates that an endurance-trained athlete can store up to 1,800 to 2,000 calories of fuel as glycogen in the muscles and liver.

Because you are burning body fat, you will be generating much higher levels of ketones. The ketones serve as the main fuel source for your cells rather than glucose.

Physically, many of the same symptoms of fasting will persist into this water fasting stage that initially appeared during the first stage of water fasting.

However, some people start to feel the benefits of burning ketones, such as improved mental clarity.

Additionally, you will start to notice a significant drop in water weight by the end of the second stage of water fasting once your glycogen has been fully depleted. 

This weight loss is attributable to the release of stored body water rather than actual fat loss.

A person standing on a scale.

Because the body stores about 3 to 4 grams of water for every gram of glycogen, once all of your glycogen has been burned off and you are not taking in more carbohydrates during a fast, your body will have released the body water.

If we go with the figure that a well-trained adult has about 600 grams of stored glycogen, and we assume that the body is storing 3 grams of water for every gram of glycogen, this means that your body might be storing around 1800 grams of water just to hold your glycogen stores.

There are about 454 grams in a pound, so if you deplete your 600 grams of glycogen and the 1800 grams of stored water, your net weight may decrease as much as 5.25 pounds in the first few stages of water fasting. 

Keep in mind that most of this is water weight, and it is extremely important to start drinking more water to prevent dehydration since your body is releasing stored water as you burn through your glycogen.

A person drinking from a bottle of water.

Stage 3: 24 Hours Of Water Fasting

After a full 24 hours of water fasting, the process of autophagy is said to begin.

Autophagy can be thought of as the clean-up process of the cells. During autophagy, dead and damaged cells and cell fragments are removed and cleaned up around your body. 

Viable cell components and proteins can be recycled and reassembled for new cells or to repair damaged cells, while damaged and misfolded proteins, such as those linked to neurodegenerative diseases like Alzheimer’s, are destroyed.

In this way, autophagy helps protect your body from such diseases and other sources of oxidative damage, inflammation, and premature aging.

At this point in the water fasting timeline, you might begin to experience the beginnings of the benefits of autophagy, such as decreased pain associated with inflammation (less joint pain, headaches, bloating, etc.), better mental focus, and potentially more energy.

This is not to say that everyone in this one of the stages of water fasting will feel great. Many people feel really hungry, irritable, lethargic, and experience brain fog. 

Again, each individual has their own unique response to hunger, energy intake, and fasting.

A blackboard that says HGH.

Stage 4: After 48 Hours of Water Fasting

After water fasting for 48 hours, the level of human growth hormone (HGH) in your body may have increased up to fivefold compared to normal resting levels.

This hormone can help rebuild and repair cells and tissues. Autophagy will still be taking place, and you will still be in a state of ketosis.

It will become increasingly important to hydrate enough and to take in electrolytes because your electrolytes may start to deplete through urine and sweat and the lack of electrolytes coming in through your diet.

Stage 5: After 60 Hours of Water Fasting

Once you have been water fasting for about 60 hours, or 2 1/2 days, your insulin levels will have dropped to their lowest level, and your cells’ sensitivity to insulin will peak.

This is particularly beneficial for anyone with insulin resistance, metabolic syndrome, or type 2 diabetes.

A person drinking a glass of water.

Stage 6: After 72 Hours Of Water Fasting

The last defined stage of prolonged water fasting is marked by your body beginning to destroy old immune cells and generate new, healthier immune cells.

This typically occurs after water fasting for 72 hours or more. It can strengthen your immune system, decrease inflammation, and boost energy and vitality.

It is important to speak with your healthcare provider before attempting a prolonged water fast. Water fasting for an extended period of time may not be safe or advisable for certain individuals.

It is also advisable to build up to extended water fasting protocols with shorter water fasts or intermediary intermittent fasting diet schedules.

Interested in trying a prolonged water fast? Check out our guide to three-day water fasting here.

A person drinking a glass 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.

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