Water Fasting: What Is It and Should You Do It? - Perfect Keto

Blog Categories


Water Fasting: What Is It and Should You Do It?


Thousands of years ago, fasting was an everyday practice. Before food was readily available (and convenience stores stood on every corner) humans went long periods without food.


Join 90k+ people who are losing weight with Keto Kickstart, our doctor-developed program designed to give you real weight loss results.

There are many different approaches to fasting, each with different benefits. The length, frequency, and number of calories (if any) allowed on a fast depend on the type of fast, and its corresponding objectives.

Below, you’ll learn about a certain type of fast called water fasting. During a water fast, you will forgo food entirely, but drink as much water as you like. Keep reading to uncover the associated risks and benefits and how to start a water fast.

What Is Water Fasting?

A water fast consists of drinking only water and completely eliminating any food intake for a minimum of 24 hours and up to three days.

There are many reasons someone may partake in a water fast. They might choose to fast for medical reasons, weight loss, heightened mental clarity, or as a religious or spiritual practice.

3 Potential Benefits of Water Fasting

Like other forms of fasting, water fasts have been linked to various physical and mental benefits, including:

#1: It Could Reduce Oxidative Stress

Oxidative stress occurs when there’s a higher number of free radicals (molecules with an uneven number of electrons) with antioxidants (molecules that “give” an electron to a free radical to make it more stable).

When this happens, free radicals can damage fatty tissue, DNA, and proteins in your body. This, in turn, is linked to diabetes, high blood pressure, heart disease, and other diseases like Parkinson’s and Alzheimer’s[*].

In a study observing the effects of an 11-day water fast, participants showed a reduction in oxidative stress, body weight, and blood pressure[*]. This shows similar results to studies observing the effect of intermittent fasting, where levels of oxidative stress and inflammation were reduced[*].

#2: It May Increase Autophagy

Autophagy is a natural (and beneficial) process where old cells are broken down and recycled. In recent years, autophagy has been shown to protect against infection and neurodegenerative diseases like Alzheimer’s.

Short-term fasting has been shown to increase autophagy[*]. Prolonged fasting, or fasts that last for two days or more, have been shown to increase autophagy, protect cells from toxins, and increase the death of various cancer cells[*].

#3: It Can Improve Insulin Sensitivity

Insulin is a hormone, secreted by the pancreas, that helps keep your blood sugar levels stable. When you eat carbohydrates and sugar, your blood glucose levels rise. This signals the release of insulin, which works to remove sugar from your bloodstream.

Browse our curated collection of fan-favorites and discover your new favorite snack or supplement.

Shop Best Sellers

Various studies show that fasting can help improve insulin sensitivity[*][*]. This means only a small amount of insulin is needed to move glucose to cells (a good thing). Insulin resistance can lead to obesity and diabetes[*].

3 Potential Risk Factors of Water Fasting

While water fasting offers many mental and physical benefits, there are some concerns that come along with it.


Join 90k+ people who are losing weight with Keto Kickstart, our doctor-developed program designed to give you real weight loss results.

For one, extreme calorie restriction over a long time can be taxing, both physically and mentally. In some cases, fasting for long periods of time can pose these potential dangers to your health:

#1: Dehydration

While this may come as a surprise, water fasts can make you become dehydrated. Up to 30% of your water intake can come from solid foods, so it is important to drink an abnormally high amount of water to make up the difference[*].

#2: You May Lose an Unhealthy Amount of Weight

On a water fast, you may lose weight extremely rapidly. On the surface, this sounds great, but it can be detrimental to your health. When you lose a great deal of weight in a very short amount of time, you might be losing water weight, or worse, muscle mass.

#3: It Can Disrupt Your Electrolyte Balance

Electrolytes play a central role in various bodily functions, supporting your digestive, nervous, cardiac, or muscular system. If you are an athlete (or were in your younger days), you probably know the oh-too-familiar feeling of muscle cramps — a side effect of an electrolyte imbalance. Unfortunately, prolonged fasting has been shown to breakdown the balance of electrolytes in your body[*].

Who Should Not Experiment With Water Fasting?

Health benefits and drawbacks aside, there are some people who should not participate in water fasting:

  • People who previously struggled with an eating disorder or disordered eating.
  • Children, teenagers, pregnant women.
  • People with thyroid problems, adrenal fatigue, autoimmune diseases, and other health issues.

An Alternative to Water Fasting: Fast Mimicking

If water fasting does not sound like a viable practice to you, there is one alternative you might consider trying: fast mimicking.

The idea of fast mimicking began with the Fasting Mimicking Diet developed by Dr. Valter Longo at the University of Southern California’s Longevity Institute. This alternative fasting diet follows a low carbohydrate, low protein, and low calorie diet, while eating high amounts of fat, for five days. It’s meant to mimic the effects of water fasting or other periodic fasting to reduce fat, promote longevity, and improve overall health.

Each day, caloric intake is kept to around 40% of regular calories. The original diet includes plant-based bars, soups, snacks, and drinks, including chamomile tea, and a supplement. Since its development, others have experimented with their own homemade versions of the diet, including Perfect Keto’s Dr. Anthony who did a ketogenic version of four-day fast mimicking.

3 Benefits of Fast Mimicking

Fast mimicking has been clinically tested with favorable results. It’s been found to:

  • Improve fasting glucose levels
  • Lessen risk factors of human disease related to aging
  • Reverse late-stage Type 1 and Type 2 diabetes[*]
  • Improve metabolism and cognition
  • Reduce the risk of cancer
  • Boost the immune system
  • Alleviate the negative effects of Alzheimer’s[*]

What’s the Difference Between Fast Mimicking and Other Types of Fasting?

Fast mimicking may sound a bit like intermittent fasting, which is a more well-known practice.

Here’s the difference: Intermittent fasting is short-term fasting (usually around 16–48 hours) used to improve health. Fast mimicking, like water fasting, is a much longer fast. Fast mimicking can last for up to five days, when eating resumes as usual.

Is Water Fasting Right for You?

Water fasting is a practice where someone abstains from food completely, but drinks as much water as they please, for a set period of time. A typical water fast lasts 24–48 hours.

Water fasting can help improve blood glucose levels, lower blood pressure, increase autophagy, and reduce oxidative stress. Unfortunately, water fasting for extended periods of time can cause dehydration, muscle loss, or an electrolyte imbalance.

Water fasting might be worth an experiment, except under certain circumstances. If you never tried fasting previously, you might consider starting with fast mimicking, which is a more moderate approach. Or, check out the Beginner’s Guide to Intermittent Fasting.


Join 90k+ people who are losing weight with Keto Kickstart, our doctor-developed program designed to give you real weight loss results.

Leave a Reply

Your email address will not be published. Required fields are marked *

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

Join the Internet's largest keto newsletter

We'll send you articles, product guides, and exclusive offers customized to your goals.