Water Fasting: What is It and is It Safe?

In the past few decades, practices like intermittent fasting and time-restricted fasting have gained wide acceptance as tools for weight loss and other (potential) health benefits. As is often the case, if a practice is proven to be effective, some people will presume it to be even more beneficial if it is taken to an extreme.

One of the extreme variations of fasting, which isn’t new but has become popular thanks in part to celebrities like UFC President Dana White, is water fasting. The belief is that you can rapidly unlock tremendous physiological improvements by lengthening the time that your body subsists on only its most essential nutrient — good old H2O. 

Meet The Expert

Laura Douglass, MD, is a board-certified obstetrician-gynecologist with fellowship training in minimally invasive gynecologic surgery. She is an assistant professor of obstetrics and gynecology at the University of Chicago’s Pritzker School of Medicine, where she is also the director of the Transabdominal Cerclage Program. Laura is a graduate of both the Wayne State University School of Medicine, and the residency program of the University of Chicago.

What is Water Fasting? 

Water fasting is the act of depriving your body of any nutrients other than water for a set period. While terms like intermittent fasting or time-restricted fasting typically apply to fasts of less than 24 hours, water fasting generally refers to fasts lasting longer than 24 hours. In some extreme cases, these fasts may extend for multiple weeks. In his viral video highlighting his own experience, Dana White said his water fast lasted 86 hours. 

The Potential Benefits of Water Fasting 

Studies indicate that there are multiple reasons why you might consider it worth the potential risks to eliminate all food and other supplements from your diet and simply drink water.

Credit: Oleggg / Shutterstock

[Read More: How Much Water Do You Really Need to Drink a Day?]

“Many religious or cultural fasts include water as an option to consume, and short-term fasting for a few days would be unlikely to yield any downsides for a healthy adult,” said Douglass. “During a short-term fast, the body converts to breaking down fat stores to extract nutrients. The downside occurs when the fast goes for too long, at which point muscle wasting will occur.”

Weight Loss 

The most obvious outcome of a water fast is losing body weight. By depriving your body of food altogether, you induce ketosis, during which your body turns to its fat stores for energy, and feeds off the resulting ketones instead of glucose. (1) Across multiple water-fast studies, participants dropped significantly, with more body fat lost than fat-free mass. (2)(3

Improved Mood 

Water fasts have been credited with improving the moods of some study participants. Some shorter-term fasting studies have shown some links between fasting and reductions in anxiety, depression, and fatigue. (4) Also, test subjects in one water-only fasting study experienced reduced anxiety following fasting, although this effect was limited to older test subjects. (5)

Lower Blood Pressure 

If you suffer from high blood pressure, a water fast may help bring it back down (though never try anything without talking to your doctor first). A medically supervised water fast of 10 to 11 days resulted in the average test subject experiencing a drop in blood pressure of 33/13 mm Hg. (6) Moreover, the test subjects with the highest initial blood pressure readings experienced the steepest declines in blood pressure.

Reduced Cholesterol 

If you find yourself plagued by chronically high cholesterol, a water fast may offer a potential solution. Similar to the case with intermittent fasting, an extended water-only fast was demonstrated to lower LDL, HDL, and total cholesterol following refeeding. (7)

Insulin Moderation

While low insulin levels are dangerous, high insulin levels are indicative of an overactive pancreas, and also a warning that type 2 diabetes might be looming. (8) Water-only fasting has proven to be an effective intervention for lowering blood sugar levels, thereby reducing the insulin present in the bodies of study subjects. In one study, the insulin levels of test subjects experienced a nearly three-fold plunge below baseline levels. (7)

The Potential Risks and Side Effects 

While the aforementioned water-fast outcomes all sound like study-backed ways to enhance negative health conditions, that’s only half of the story. In most cases, studies exploring the outcomes of water-only fasting have unearthed undeniably dangerous side effects of this type of fasting. If you ever intend to participate in a water-only fast, these risks to your well-being should be considered.

Credit: Shine Nucha / Shutterstock

[Read More: 8 Natural Ways to Decrease Appetite]

“A fast of only a few days would be unlikely to cause serious issues, but if it were prolonged, nausea and GI upset would be among the most mild problems that could happen,” explains Douglass. “This is especially true if negative consequences like muscle wasting occurred during the fast.”

Low Energy 

Extended water-only fasting deprives your body of macronutrients and micronutrients deemed essential for optimal energy production. Most study results suggest that fasting is either detrimental to athletic performance, or has no effect. (9)(10) However, there are no strong indications that your physical performance will improve once your body enters a fasted state. 

Elevated Irritability 

As your body begins to recognize the loss of the nutrients it craves, you will probably experience a downturn in mood, or an increase in irritability. Micronutrients like B vitamins, vitamin D, magnesium, zinc, selenium, iron, calcium, and omega-3 fatty acids are all linked with optimal brain and nervous system function. Deficiencies of these nutrients have been linked with depressive symptoms. (11)

Disordered Eating Encouragement 

The results of at least one study found that fasting contributed to the practice of disordered eating. (12) For the record, the study in question specifically involved intermittent fasting and its effects on adolescents. However, it is worth considering the likelihood that regular water fasting might introduce you to a pattern of unhealthy dietary behaviors, like extended food avoidance.

[Read More: 9 Types of Diets — How They Work and Pros & Cons]

Harmful Metabolic Effects 

As a consequence of an eight-day water fast, test subjects experienced several dangerous metabolic issues. This included low serum sodium levels, elevated uric acid levels in their blood, hypoglycemia, and aggravated ketogenesis. (3) Several of these conditions have been linked with diagnoses of gout and kidney stones.

Heightened Insulin Sensitivity

While studies have shown that water-only fasting decreases insulin levels, they also indicate a subsequent increase in insulin resistance. (13)(14) In response to insulin sensitivity, your pancreas will make even more insulin, a general characteristic of prediabetes. As such, while water fasting may temporarily reduce the insulin present in your body, it may increase the likelihood of greater future insulin overproduction. 

Compromised Muscle Recovery 

Eliminating nutrients from your diet means you will not get the recommended amount of protein to repair your muscle tissue after exercise. (15) As a result, lifting heavy weights during prolonged fasting will leave microtears in your muscle fibers without sufficient amino acids available to repair them. (16) This will lead to reduced muscle mass and muscle weakening over time. 

[Read More: How Much Water Do You Actually Need While Training?]

Diminished Health Hormones

Over the course of a five-day water-only fast, participants lost an average of 26 percent of their IGF-1, which is a hormone that contributes to tissue growth in adults, including muscle growth. In addition, participants in the study lost a significant number of B cells and T cells, both of which are white blood cells that are vital to warding off illnesses. (7)

Refeeding Syndrome

If you participate in a fast lasting more than five days, you are at high risk for fatal refeeding problems. (17) Even if all goes well during your fast, low levels of potassium, phosphate, or magnesium are likely to bring about refeeding syndrome. This is a condition marked by adverse effects ranging from muscle weakness and vomiting to seizures, coma, and potential death.

[Read More: How To Stay Hydrated While Working Out]

A Word on Water Fasting for Weight Loss 

BarBend deems all recommended macronutrients and most micronutrients essential to maintaining proper bodily functions. Therefore, we do not advise our readers to casually participate in water fasts. Even if you have been diagnosed with a medical condition for which water fasting has been deemed an appropriate medical intervention, a water fast should only be observed under the care of a licensed healthcare professional.

[Read More: Learn How to Make a Homemade Electrolyte Drink from a Certified Nutrition Coach]

“As with most diets taken for quick weight loss, you probably won’t sustain the losses for very long after the fast ends,” advises Douglass. “Going without food for long periods of time is dangerous, and the longer a fast goes, the more difficult it is to bring you out of it safely. And if you’re doing all of this for long-term weight loss, a water fast is unlikely to give you a true edge.” 

Should You Try Water Fasting? 

While medically supervised water fasting appears to result in some physical benefits to those who follow it, results have been mixed. Any potential positive outcomes of water fasting appear to be accompanied by detrimental consequences. As such, you should exercise extreme caution before you choose to embark on a water fast, as there is an elevated risk that you may not emerge from such a fast completely unscathed.

“Personally, I would never advise someone to begin a water fast, not even post-op patients,” insists Douglass. “That’s because early feeding — especially of carbohydrates before and after surgery — yields better recovery and return of bowel function, with less morbidity. I could never advise a healthy person to undertake such a dangerous course of action on their own.”


If you still have questions about the safety and efficacy of water fasting, we provide clear answers for you here.

Can you lose weight by water fasting? 

Study results indicate that you can lose significant weight by water fasting. Test subjects involved in one 10-day controlled water fast lost an average of 10 percent of their body weight, amounting to an average of 16 pounds per subject. (2) Moreover, a higher percentage of the weight lost consisted of body fat, and the majority of the lost body fat remained absent following post-fast refeeding.

How long can you water fast for?

According to expert opinion, a healthy person can survive for up to two months (in extreme cases) on water alone. (18) However, water fasts lasting longer than five days create circumstances under which refeeding must be conducted very carefully to avoid potentially fatal consequences. (17)

How can I break a water fast?

How you should break a water fast depends upon its length. The National Institute for Health and Clinical Excellence advises that refeeding begins at no more than 50 percent of your energy requirements if you’ve been fasting for over five days. (17) Furthermore, it is advised that refeeding begins only after your plasma electrolyte levels have been carefully measured by a medical professional in order to avoid adverse events.

What are the risks of water fasting?

Water fasting has many risks. During a water fast, you are likely to experience increased irritability, a reduction in energy, compromised muscle repair, potential kidney damage, and reduced levels of key hormones. Following the fast, you are also at risk of refeeding syndrome, which is a potentially fatal condition.


Masood W, Annamaraju P, Khan Suheb MZ, et al. Ketogenic Diet. [Updated 2023 Jun 16]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499830/

Dai Z, Zhang H, Wu F, Chen Y, Yang C, Wang H, Sui X, Guo Y, Xin B, Guo Z, Xiong J, Wu B, Li Y. Effects of 10-Day Complete Fasting on Physiological Homeostasis, Nutrition and Health Markers in Male Adults. Nutrients. 2022 Sep 18;14(18):3860. doi: 10.3390/nu14183860. PMID: 36145236; PMCID: PMC9503095.

Ogłodek E, Pilis Prof W. Is Water-Only Fasting Safe? Glob Adv Health Med. 2021 Aug 5;10:21649561211031178. doi: 10.1177/21649561211031178. PMID: 34414015; PMCID: PMC8369953.

Wang Y, Wu R. The Effect of Fasting on Human Metabolism and Psychological Health. Dis Markers. 2022 Jan 5;2022:5653739. doi: 10.1155/2022/5653739. PMID: 35035610; PMCID: PMC8754590.

Stec K, Pilis K, Pilis W, Dolibog P, Letkiewicz S, Głębocka A. Effects of Fasting on the Physiological and Psychological Responses in Middle-Aged Men. Nutrients. 2023 Aug 3;15(15):3444. doi: 10.3390/nu15153444. PMID: 37571381; PMCID: PMC10421233.

Goldhamer A, Lisle D, Parpia B, Anderson SV, Campbell TC. Medically supervised water-only fasting in the treatment of hypertension. J Manipulative Physiol Ther. 2001 Jun;24(5):335-9. doi: 10.1067/mmt.2001.115263. PMID: 11416824.

Jiang Y, Yang X, Dong C, Lu Y, Yin H, Xiao B, Yang X, Chen W, Cheng W, Tian H, Guo L, Hu X, Fang H, Chen W, Li Z, Zhou W, Sun W, Guo X, Li S, Lin Y, He R, Chen X, Liu D, Zhang M, Zhang Y, Zhao H, Zheng P, Seyfried TN, Hoffman RM, Jia W, Ji G, Jia L. Five-day water-only fasting decreased metabolic-syndrome risk factors and increased anti-aging biomarkers without toxicity in a clinical trial of normal-weight individuals. Clin Transl Med. 2021 Aug;11(8):e502. doi: 10.1002/ctm2.502. PMID: 34459130; PMCID: PMC8320652.

CDC – Insulin Resistance and Diabetes. https://www.cdc.gov/diabetes/basics/insulin-resistance.html. January 22, 2024.

Gleeson M, Greenhaff PL, Maughan RJ. Influence of a 24 h fast on high intensity cycle exercise performance in man. Eur J Appl Physiol Occup Physiol. 1988;57(6):653-9. doi: 10.1007/BF01075984. PMID: 3416848.

Eroglu, M.N.; Rodríguez-Longobardo, C.; Ramírez-Adrados, A.; Colina-Coca, C.; Burgos-Postigo, S.; López-Torres, O.; Fernández-Elías, V.E. The Effects of 24-h Fasting on Exercise Performance and Metabolic Parameters in a Pilot Study of Female CrossFit Athletes. Nutrients 2023, 15, 4841.

Zielińska M, Łuszczki E, Dereń K. Dietary Nutrient Deficiencies and Risk of Depression (Review Article 2018-2023). Nutrients. 2023 May 23;15(11):2433. doi: 10.3390/nu15112433. PMID: 37299394; PMCID: PMC10255717.

Ganson KT, Cuccolo K, Hallward L, Nagata JM. Intermittent fasting: Describing engagement and associations with eating disorder behaviors and psychopathology among Canadian adolescents and young adults. Eat Behav. 2022 Dec;47:101681. doi: 10.1016/j.eatbeh.2022.101681. Epub 2022 Nov 4. PMID: 36368052.

Scharf 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.

Sanvictores T, Casale J, Huecker MR. Physiology, Fasting. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534877/

van Loon LJ. Role of dietary protein in post-exercise muscle reconditioning. Nestle Nutr Inst Workshop Ser. 2013;75:73-83. doi: 10.1159/000345821. Epub 2013 Apr 16. PMID: 23765352.

Campbell BI, Aguilar D, Conlin L, Vargas A, Schoenfeld BJ, Corson A, Gai C, Best S, Galvan E, Couvillion K. Effects of High Versus Low Protein Intake on Body Composition and Maximal Strength in Aspiring Female Physique Athletes Engaging in an 8-Week Resistance Training Program. Int J Sport Nutr Exerc Metab. 2018 Nov 1;28(6):580-585. doi: 10.1123/ijsnem.2017-0389. Epub 2018 Jul 3. Erratum in: Int J Sport Nutr Exerc Metab. 2020 Sep 1;30(5):383. PMID: 29405780.

Mehanna HM, Moledina J, Travis J. Refeeding syndrome: what it is, and how to prevent and treat it. BMJ. 2008 Jun 28;336(7659):1495-8. doi: 10.1136/bmj.a301. PMID: 18583681; PMCID: PMC2440847.

Kottusch P, Tillmann M, Püschel K. Oberlebenszeit bei Nahrungs- und Flüssigkeitskarenz [Survival time without food and drink]. Arch Kriminol. 2009 Nov-Dec;224(5-6):184-91. German. PMID: 20069776.

Featured Image: Oleggg / Shutterstock

The post Water Fasting: What is It and is It Safe? appeared first on BarBend.


您的电子邮箱地址不会被公开。 必填项已用 * 标注