Is Water Fasting Safe? Benefits and Risks

By Ashley LoseMay 28th 2021

Fasting is a practice dating back thousands of years where you abstain from eating foods for a specific period of time. It’s a ritual that’s been traced back to ancient civilizations like the Greeks, Chinese, and Romans who primarily fasted for medical and spiritual purposes.1 Nowadays, we have an array of fasting styles to choose from – intermittent, alternate day, eat-stop-eat, periodic, dry fasting, and they’ve all become popular fads for rapid weight loss results. 

One fasting approach that’s growing in popularity across the web is water fasting. The water fasting approach to weight loss is restricting every – food and drinks – except for water. While not all of these fasting methods have been scientifically proven to be effective or safe, adepts of water fasting claim this approach might have some health benefits. For one, water is fundamental to the human body which itself is 60% water. 2 The vital substance plays a role in regulating our internal body temperature, transporting carbohydrates and proteins into our bloodstream, lubricates our joints, and assists us in flushing waste from our bodies, mainly through urination.3 

Food is essential to our bodies too. One study claimed that people can’t go more than 8 to 21 days without food or water before dying.4 However, it is said that water plays a much more integral role in our bodies than food. Without water, your body would shut down much faster than it would from simply abstaining from food. And sadly there are still around 783 million people worldwide who do not have access to safe drinking water.5

Is Water Fasting Safe? Benefits and Risks

Without water, our bodies are at extreme risk of dehydration. This could look different for everyone but symptoms are as follows:6 

  • Feeling very thirsty
  • Dry mouth
  • Urinating and sweating less than usual
  • Dark-colored urine
  • Dry skin
  • Feeling tired
  • Dizziness

In this article, we’ll explore the health benefits of water fasting, its potential risks, and identify if it’s a safe and effective strategy for your weight loss goals.

What Is Water Fasting?

When implementing a water fast diet, you’ll cut everything out of your diet except water. You’re encouraged to abstain from food and avoid drinking sodas, smoothies, and other beverages besides water. Similar to the Eat Stop Eat diet, water fasting typically lasts for about 24 to 72 hours. Considering plain water is calorie-free and devoid of nutrients 7 it is not recommended that you stay on a water diet for longer than  72 hours without medical supervision. 

Is Water Fasting Safe? Benefits and Risks

How To Start A Water Fast?

While short-term fasting is presumed to be relatively safe for healthy adults, there is no scientific evidence or guidelines on how you should best administer a water fast diet. 

To begin a water fast, some people recommend that you begin by preparing your body 3 to 4 days in advance. You can do this by eating smaller portions of food each day in preparation for the amount of time you’re about to go without food. Typically, people on a water fast diet consume two to three liters of water. 

Is Water Fasting Safe? Benefits and Risks

After your fasting period, you should slowly reintroduce foods into your body and avoid the urge to binge or eat one big meal. You can start with a smoothie, nuts, or other smaller meals to avoid uncomfortable symptoms that come from eating after days of fasting. Fasting and then returning to meals can put you at risk of what is known as refeeding syndrome. It’s a serious and potentially fatal condition that comes from being malnourished or starved and then eating large amounts of food. When your body is recovering from malnutrition or starvation, your body undergoes changes in the way it metabolizes nutrients.8 This process could last for about 24 hours, but people who stay on a water fast for longer may need up to three days to recover. You can slowly introduce bigger meals into your diet as you feel comfortable. 

Benefits of Water Fasting Diet

People gravitate towards the water fasting diet for various reasons: 

  • Weight loss
  • Spiritual or religious practices 
  • Preparing for a medical procedure

Whatever the reason, they’re hoping to receive some sort of health benefits that can improve their overall wellness. Studies on mice show that water-only fasting methods could potentially have significant effects on a person's health including lowering their risk of chronic diseases such as diabetes, heart disease, and some cancers.9,10,11 It could also promote autophagy, which is the body's natural mechanism of removing damaged cells and regenerating newer, healthier cells in the body.12 

Is Water Fasting Safe? Benefits and Risks

In terms of weight loss, water-only fasting has also produced convincing results. This is primarily due to the fact that you aren’t eating which is a significant reduction in your calorie intake. By doing so, your body will naturally burn more calories than you’re consuming, thus promoting weight loss.13 Some people are highly successful in losing weight using this method because they are able to avoid snacking and adhere to the rules of water fasting. Studies show that consuming water throughout your day not only helps you stay hydrated but can also help you stay on track with your fast by decreasing your cravings. 14 

While water fasting has been linked to weight loss and lowering your risk of chronic diseases, it’s important to note that it is not for everyone and also comes with many risks to the human body, especially if it is followed for too long. 

Water Fasting Health Risks 

Another danger of water fasting is it may cause you to lose the wrong type of weight. Water fasting is an intense calorie-restricted diet and will make you lose weight at a rapid pace. Research shows that you can lose up to 2 pounds a day on a 24- to 72-hour water fast. 15 This can be in water weight, carbohydrates, or even muscle loss which you want to avoid. 

Although a water-only fast is relatively short, it could come with grave health risks. If you have a history of eating disorders, diabetes, gout, or are pregnant you should not start a water fast without medical supervision.16 

Is Water Fasting Safe? Benefits and Risks


  1. Anton, S. D., Moehl, K., Donahoo, W. T., Marosi, K., Lee, S. A., Mainous, A. G., 3rd, Leeuwenburgh, C., & Mattson, M. P. (2018). Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring, Md.), 26(2), 254–268.

  1. Kottusch, P., Tillmann, M., & Püschel, K. (2009). Oberlebenszeit bei Nahrungs- und Flüssigkeitskarenz [Survival time without food and drink]. Archiv fur Kriminologie, 224(5-6), 184–191.

  1. United Nations. (n.d.). Human right to water and sanitation. International Decade for Action "Water for Life" 2005-2015.

  1. Medline Plus. (n.d.). Dehydration. Health Topics.

  1. U.S. Department of Agriculture. (n.d.). Water, tap. FoodData Central.

  1. Mehanna, H. M., Moledina, J., & Travis, J. (2008). Refeeding syndrome: what it is, and how to prevent and treat it. BMJ (Clinical research ed.), 336(7659), 1495–1498.

  1. Alirezaei, M., Kemball, C., Flynn, C., Wood, M., Whitton, J. L., Kiosses, W., & Autophagy. (2010, August 14). Short-term fasting induces profound neuronal autophagy.

  1. Castello, L., Froio, T., Maina, M., Cavallini, G., Biasi, F., Leonarduzzi, G., Donati, A., Bergamini, E., Poli, G., & Chiarpotto, E. (2010). Alternate-day fasting protects the rat heart against age-induced inflammation and fibrosis by inhibiting oxidative damage and NF-kB activation. Free radical biology & medicine, 48(1), 47–54.

  1. Brandhorst, S., Choi, I. Y., Wei, M., Cheng, C. W., Sedrakyan, S., Navarrete, G., Dubeau, L., Yap, L. P., Park, R., Vinciguerra, M., Di Biase, S., Mirzaei, H., Mirisola, M. G., Childress, P., Ji, L., Groshen, S., Penna, F., Odetti, P., Perin, L., Conti, P. S., … Longo, V. D. (2015). A Periodic Diet that Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance, and Healthspan. Cell metabolism, 22(1), 86–99.

  1. Glick, D., Barth, S., & Macleod, K. F. (2010). Autophagy: cellular and molecular mechanisms. The Journal of pathology, 221(1), 3–12.

  1. Redman, L. M., & Ravussin, E. (2011). Caloric restriction in humans: impact on physiological, psychological, and behavioral outcomes. Antioxidants & redox signaling, 14(2), 275–287.

  1. Van Walleghen, E. L., Orr, J. S., Gentile, C. L., & Davy, B. M. (2007). Pre-meal water consumption reduces meal energy intake in older but not younger subjects. Obesity (Silver Spring, Md.), 15(1), 93–99.

  1. Kerndt, P. R., Naughton, J. L., Driscoll, C. E., & Loxterkamp, D. A. (1982). Fasting: the history, pathophysiology and complications. The Western journal of medicine, 137(5), 379–399.

  1. Kerndt, P. R., Naughton, J. L., Driscoll, C. E., & Loxterkamp, D. A. (1982). Fasting: the history, pathophysiology and complications. The Western journal of medicine, 137(5), 379–399.

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