Water Fasting: Benefits, Side Effects, and How To Do It

Water fasting is one of my favorites among all the types of fasting as it is straightforward to follow and shows promising results. This post is perfect if you’re considering water fasting to improve overall health.

In this article, you will discover everything you need to know about water fasting, including how to do it, its benefits and potential risks, and who should not be doing it.

Key Takeaways:

  • During water fasting, you only drink water.
  • Most water fasts last 1-3 days, and some 7+ days.
  • It can improve weight loss, type 2 diabetes, heart, and neurodegenerative diseases.

Table of Contents:

What Is Water Fasting?

Water fasting involves consuming only water for 24 to 72 hours.

The method is also known as prolonged or extended fasting or zero-calorie diet.

It is a practice that extends back to ancient times, finding roots in historical records dating back to the 5th century.

Fasting for health reasons can be traced to the ancient Greek physician Hippocrates. Still, experts date back water fasting to the days of Paryushan in Jainism or the eucharistic fast of Roman Catholicism.

Scientifically, water fasting is a form of strict caloric restriction, triggering physiological changes in the body. During a water fast, the absence of caloric intake induces autophagy and ketosis, which have numerous benefits.

How to Water Fast

Embarking on a water fast requires careful planning and consideration to ensure safety and efficacy.

While water fasting lacks a standardized medical protocol, you can follow expert guidelines for a more structured approach.

water fasting woman

Duration and Preparation

Many practitioners start with shorter fasts, typically 24 hours, to acclimate the body. If you plan on going for more prolonged fasts, ranging from 48 hours to 72 hours, approach it cautiously, especially for beginners.

Preparing for a fast involves gradually reducing meal sizes before the fast, allowing the body to adjust to lower caloric intake.

For enthusiasts, water fasting for longer than 7 days could be beneficial without putting themselves at any risk. Still, beginners should consult medical supervision to go beyond the 72-hour water fasting.

Hydration and Electrolytes

Staying adequately hydrated is crucial during a water fast. Consuming 2-3 liters of water per day helps prevent dehydration, a standard risk during extended fasting.

Experts recommend choosing mineralized water or electrolyte-infused water to maintain essential minerals.

You can also consider electrolytes and other fasting supplements to prevent imbalances.

Breaking the Fast

How a water fast concludes is as crucial as its initiation. Breaking the fast should be done gradually and mindfully.

Opting for a smaller meal, preferably a bone broth rich in proteins and healthy fats, helps the digestive system ease back into food consumption.

A sudden return to a regular diet, especially one high in carbohydrates, can lead to digestive discomfort and potential health risks.

Consider Professional Guidance

While some individuals undertake water fasting independently, others seek guidance from healthcare providers, particularly for longer or medically supervised fasts.

Specific alternative health centers or naturopathic doctors offer programs with structured fasting periods, often requiring medical referrals for participation.

Benefits of Water Fasting

Weight Loss

One of the primary motivations for water fasting is weight loss. The process induces a state of nutritional ketosis, where the body shifts from burning glucose to utilizing stored fat for energy.

In a study of 12 healthy, middle-aged men who underwent an 8-day water fast1 with only mineral water, the mean body weight dropped from 79.38 Kg to 73.42 Kg, body surface area dropped from 1.98 m2 to 1.90 m2, and BMI dropped from 24.89 to 23.02, after only water fasting for 8 days.

A 2023 study also reveals that prolonged fasting for 5-20 days2 produces potent increases in circulating ketones and mild to moderate weight loss of 2-10%. Approximately two-thirds of the weight lost is lean mass, and one-third is fat mass. The only concern is the possible muscle protein breakdown in more prolonged water fasting.

Type 2 Diabetes Management

Fasting may play a role in managing type 2 diabetes by improving insulin sensitivity. Some studies indicate that individuals with diabetes3 who undergo fasting experience a reduction in their reliance on diabetes medications, including insulin, due to weight loss.

However, some short-term studies in water fasting suggest that there are no metabolic changes that may benefit those who have diabetes.

Nevertheless, weight management is an established way to lower the risk of progression to type 2 diabetes4 among people with prediabetes and reduce diabetes complications.

Cardiovascular Health

Water fasting may positively affect cardiovascular health by reducing risk factors such as hypertension and high cholesterol.

In a study from 2001, 174 subjects with known hypertension participated in a medically supervised fasting of 10-11 days.

Results show that 90% of them achieved blood pressure less than 140/90 mmHg5 by the end of the water fast.

Moreover, subjects taking antihypertensive medications before doing the water fast discontinued the use after the results.

Some studies suggest that fasting can contribute to improving lipid profiles.6

These cardiovascular benefits may be attributed to reduced oxidative stress and the induction of nutritional ketosis.

Cellular Repair and Disease Prevention

Autophagy, a cellular process stimulated by fasting,7 involves the removal of damaged or dysfunctional cellular components.

This process is crucial for cellular repair and is associated with a lower risk of various diseases, including cancer8 and neurodegenerative conditions like Alzheimer’s.9

Fasting-induced autophagy is a potential mechanism for reducing the risk of these diseases.

Potential Risks and Side Effects


One of the primary concerns during water fasting is dehydration. Since fasting involves abstaining from food, which typically contributes to about 20% of daily water intake, individuals must pay extra attention to staying hydrated.

Drinking 2-3 liters of water per day is crucial, and some may opt for electrolyte-infused water to maintain the balance of essential minerals. Factors like hot weather, diuretic use, old age, and higher altitudes can further increase the risk of dehydration during fasting.

Orthostatic hypotension

Water fasting may lead to orthostatic hypotension,10 a condition characterized by a sudden drop in blood pressure upon standing, resulting in dizziness, especially when you’re not hydrating enough. This can pose a risk of falls and injuries.

Individuals with a history of low blood pressure should approach water fasting cautiously and may need to monitor their blood pressure regularly to prevent complications.


Some individuals may experience difficulty falling asleep or disrupted sleep patterns during water fasting. Studies suggest that being in a state of starvation can affect sleep,11 reducing slow-wave sleep or deep sleep.

While insomnia during water fasting is typically temporary, maintaining proper hydration, incorporating electrolytes, and gradually introducing fasting into one’s routine can improve sleep quality.


Rapid weight loss,12 often associated with fasting, causes the liver to secrete more cholesterol into the bile, forming gallstones. Gallstones can lead to complications if not managed carefully.

Individuals may consider shorter fasting durations and gradual weight loss to mitigate this risk. Breaking a fast should be done cautiously, avoiding heavy, high-fat meals that could trigger gallstone-related issues.

glass of water for fasting

Who Should Not Try Water Fasting?

Individuals with specific conditions or circumstances should exercise caution or avoid water fasting altogether:

  • Pregnant and Breastfeeding: Increased nutritional needs during pregnancy and breastfeeding make water fasting unsuitable.
  • Type 1 Diabetes: Individuals with Type 1 diabetes should avoid water fasting to lower the risk of developing diabetic ketoacidosis.
  • Cholelithiasis or Gallstones: Rapid weight loss results in gallstone formation, and those at risk for developing them should avoid water fasting.
  • Blood Pressure and Glucose-Lowering Medications: Those taking blood pressure or glucose control medications should seek medical advice before fasting, as water fasting may cause orthostatic hypotension.
  • History of Eating Disorders: Individuals with a history of eating disorders may be prone to disordered eating behaviors during fasting.
  • GERD and Heartburn: Fasting can exacerbate symptoms of gastroesophageal reflux disorder (GERD) and heartburn.

How Long Is It Safe to Water Fast?

The recommended water fasting duration for beginners is 24-72 hours.

The safe length of water fasting durations is yet to be established, as it mainly relies on one’s health and tolerance.

However, some medically-supervised water fasting studies13 have recorded the following durations:

  • Short: 2–7 days
  • Medium: 8–14 days
  • Long: 15–21 days
  • Extended: 22+ days

It’s important to note that the safety of water fasting duration is highly individualized. Factors such as age, overall health, medical history, and existing conditions play a crucial role.

Regardless of the fasting duration, paying attention to your body’s signals is paramount. If at any point during fasting you experience severe discomfort, dizziness, or other concerning symptoms, it’s advisable to break the fast and seek medical advice.

My Experience

Few people know extended fasting is a cheat code for long-term weight loss.

It not only helps to break through a weight loss plateau but also boosts your metabolism long-term.

Scientists14 have already proven in 1964 that prolonged periods of fasting increase the basal metabolic rate.

I use 7-day water fasts twice yearly to ramp up my metabolism and prevent disease through deep autophagy.

My tip is to use a fixed date for an annual water fast. In my case, I do it traditionally in the Holy Week before easter.

This way, you have no excuses and can stick to an annual prolonged fast. Let’s be honest: there will always be an occasion to make a week not ideal for long-term fasts.

Frequently Asked Questions

Do you lose fat while water fasting?

You lose stored fat while water fasting because the body must burn it for energy (ketosis).

How much weight do you lose in 3 days with a water fast?

In 72 hours of water fasting, you will lose about 4 to 7 pounds.

What happens if you don’t eat for 7 days?

During my multiple 7-day water fasts, I always lost 13 to 15 pounds.

What are the results of the 20-day water fast?

A 20-day water fast will put you into deep ketosis and autophagy, resulting in severe loss of body fat and cell rejuvenation.

How much weight do you regain after a water fast?

After a 7-day fast, you will regain approximately 4 to 7 pounds of water weight.


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2Ezpeleta, M., Cienfuegos, S., Lin, S., Pavlou, V., Gabel, K., & Varady, K. A. (2023). Efficacy and safety of prolonged water fasting: a narrative review of human trials. Nutrition reviews, nuad081. Advance online publication. https://doi.org/10.1093/nutrit/nuad081

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4Ryan, D. H., & Yockey, S. R. (2017). Weight Loss and Improvement in Comorbidity: Differences at 5%, 10%, 15%, and Over. Current Obesity Reports, 6(2), 187. https://doi.org/10.1007/s13679-017-0262-y

5Goldhamer, A., Lisle, D., Parpia, B., Anderson, S. V., & Campbell, T. C. (2001). Medically supervised water-only fasting in the treatment of hypertension. Journal of manipulative and physiological therapeutics, 24(5), 335–339. https://doi.org/10.1067/mmt.2001.115263

6Scharf E, Zeiler E, Ncube M, Kolbe P, Hwang SY, Goldhamer A, Myers TR. The Effects of Prolonged Water-Only Fasting and Refeeding on Markers of Cardiometabolic Risk. Nutrients. 2022 Mar 11;14(6):1183. doi: 10.3390/nu14061183. PMID: 35334843; PMCID: PMC8951503.

7Wang Y, Xu Y, Wu Y, Mahmood T, Chen J, Guo X, Wu W, Wang B, Guo Y, Yuan J. Impact of Different Durations of Fasting on Intestinal Autophagy and Serum Metabolome in Broiler Chicken. Animals (Basel). 2021 Jul 23;11(8):2183. doi: 10.3390/ani11082183. PMID: 34438641; PMCID: PMC8388447.

8Bhutia SK, Mukhopadhyay S, Sinha N, Das DN, Panda PK, Patra SK, Maiti TK, Mandal M, Dent P, Wang XY, Das SK, Sarkar D, Fisher PB. Autophagy: cancer’s friend or foe? Adv Cancer Res. 2013;118:61-95. doi: 10.1016/B978-0-12-407173-5.00003-0. PMID: 23768510; PMCID: PMC4349374.

9Uddin, M. S., Stachowiak, A., Mamun, A. A., Tzvetkov, N. T., Takeda, S., Atanasov, A. G., Bergantin, L. B., Abdel-Daim, M. M., & Stankiewicz, A. M. (2018). Autophagy and Alzheimer’s Disease: From Molecular Mechanisms to Therapeutic Implications. Frontiers in Aging Neuroscience, 10. https://doi.org/10.3389/fnagi.2018.00004

10Christensen, K. A., & Short, N. A. (2021). The Case for Investigating a Bidirectional Association between Insomnia Symptoms and Eating Disorder Pathology. The International Journal of Eating Disorders, 54(5), 701. https://doi.org/10.1002/eat.23498

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12Finnell JS, Saul BC, Goldhamer AC, Myers TR. Is fasting safe? A chart review of adverse events during medically supervised, water-only fasting. BMC Complement Altern Med. 2018 Feb 20;18(1):67. doi: 10.1186/s12906-018-2136-6. PMID: 29458369; PMCID: PMC5819235.

13DRENICK, E. J., SWENDSEID, M. E., BLAHD, W. H., & TUTTLE, S. G. (1964). PROLONGED STARVATION AS TREATMENT FOR SEVERE OBESITY. JAMA, 187, 100–105. https://doi.org/10.1001/jama.1964.03060150024006

Mag. Stephan Lederer, MSc.

Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.

Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.

Click on the links above to visit his author and about me pages.

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