Water fasting: drinking more water for fasting

Water fasting is one of the many variation of intermittent fasting. Discover how it works and if it can be a good fit for you.
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Water fasting is a form of fasting that limits the consumption of everything except water. It has become more popular in recent years as a rapid weight loss method.

Written by
Dr. Sara Diana Garduno Diaz
PhD & Senior Nutrition Consultant

How water fasting works

Water fasting is a type of fast during which you cannot consume anything besides water. It is different than other forms of fasting where most of the times, you can consume various forms of liquid. Usually the water fasting period lasts between 24-72 hours. People engage in this type of fasting for various reasons, including religious practices, the desire to lose weight, in preparation for medical procedures, as a form of cleansing, and for other possible health benefits. These health benefits however have not been extensively researched by rigorous studies to date. 

When on a water fast, people are allowed to drink as much water as their heart desires. Typically, most people drink two to three liters of water per day during a water fast. Following this period it is best to ease out of the fast by consuming light foods that are easy to digest. It is recommended that large, heavy meals be avoided immediately after completing a water fast. 

Regarding the recommended amount of water to drink during a water fast, some factors, including activity level, environment, and overall health, still influence it. Therefore, while the targeted daily recommendation is between 2-3 liters of water per day, this does not mean that one should not drink more if feeling thirsty or dehydrated. While overdrinking can increase the risk of water intoxication, also called hyponatremia, this is rare.

Hyponatremia occurs when water and salt lost through sweating is replaced by only water. This can occur with water fasting when the person is not eating the required food to replenish the salt needed for the body before and after following the fasting period.

Possible benefits of water fasting

Various possible health benefits may take place as a result of water fasting. These include setting off the process of autophagy, meaning the killion off of faulty cells in the body and the trigger to create new fresh cells. Water fasting also helps getting into ketosis faster, find more about it in our dedicated article.

In addition, water fasting may help lower blood pressure, improve insulin sensitivity (thus regulating blood sugar levels), and lead to weight loss. Some more recent studies have even suggested potential beneficial effects of water fasting on kidney function and oxidative stress (which may improve the aging process). 

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What to expect when water fasting

A glass filled with water.

Some people may experience a sense of  weakness or dizziness during a water fast. This is often to be expected, especially among those trying a water fast for the first time. If this is the case, it is recommended that daily activities be adjusted during a water fasting period in order to avoid accidents.

For example, if it is possible it is better to avoid driving or operating heavy machinery during a water fast. Additionally, rest is very important as energy supplies to the body will be limited. 

What to do following a water fast

There are various steps that can be followed once a water fasting period is completed to create a more enjoyable wrap-up of the experience. For example, as it was mentioned before, breaking a water fast with a large meal is to be avoided. Instead, it is advised to break the fast with a smoothie or clear soup. Larger meals can then start to be introduced throughout the day.

Refeeding syndrome

The period following a water fast is particularly important after longer lasting fasts. This is because a person who has just avoided food for a while may be at risk of refeeding syndrome. This is a potentially fatal condition in which the body undergoes rapid changes in fluid and electrolyte levels. Electrolytes are salts found naturally in the body that help regulate muscle contraction (including heart beat). 

Who should avoid water fasting

While possible health benefits exist from following a water fast, it is not a practice recommended for everyone. For example, people who have diabetes, pregnant women and the elderly are not advised to practice water fasting. Similarly, children are advised against water fasting since the practice might compromise their required energy and nutrient intake. 

Find more information about what is intermittent fasting here.


  1. Gustafson, Craig. "Alan Goldhamer, dc: Water Fasting—The Clinical Effectiveness of Rebooting Your Body." Integrative Medicine: A Clinician's Journal 13.3 (2014): 52.
  2. Mojto, V., et al. "Effects of complete water fasting and regeneration diet on kidney function, oxidative stress and antioxidants." Bratislavske lekarske listy 119.2 (2018): 107-111.
  3. Finnell, John S., et al. "Is fasting safe? A chart review of adverse events during medically supervised, water-only fasting." BMC complementary and alternative medicine 18.1 (2018): 1-9.
  4. Blondheim, David S., Orna Blondheim, and S. H. Blondheim. "The dietary composition of pre-fast meals and its effect on 24 hour food and water fasting." IMAJ-RAMAT GAN- 3.9 (2001): 657-662.
  5. Eriksson, L. I., and R. Sandin. "Fasting guidelines in different countries." Acta anaesthesiologica scandinavica 40.8P2 (1996): 971-974.

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