The 24 Hour Water Fast: A Complete Guide [How To + What To Expect]

Our nutrition coach discusses if fasting for a full 24 hours is safe and healthy for you.

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Intermittent fasting has become a very popular approach to dieting, weight management, and improving health.

There are different styles of intermittent fasting, the most common of which is time-restricted eating, in which the window of time that you are permitted to eat in a day is limited while the overnight fast is extended as long as possible.

For example, 18/6 intermittent fasting involves fasting for 18 hours per day and then confining all of your eating and caloric intake to six hours per day.

The other approach is alternate-day fasting, in which you usually fast for a full 24 hours every other day and then consume your regular diet in between each fasting day, though some people also just reduce caloric intake every other day rather than fast completely.

If you follow the alternative day-eating approach to intermittent fasting, doing a 24 hour water fast might become a routine for you, or you might just want to try a 24 hour water fast every so often as a dietary reset.

If either of these cases applies to you, or you’re not sure how to do a 24 hour water fast, keep reading to learn how to do a 24 hour water fast, what to expect, the benefits of a 24 hour water fast, and tips for getting through a 1 day water fast.

A person with empty pates and three glasses of water in front of him, symbolizing a 24 hour fast.

What Is a 24 Hour Water Fast?

Before we look at the potential health benefits of water fasting and how to do water-only fasting, it’s important to present the disclaimer that I am a certified nutrition coach with a master’s degree in Exercise Science and Nutrition.

However, I am not a registered dietitian (RDN) nor a healthcare professional, so this should not be taken as medical advice.

Water fasting is not safe for certain individuals, especially those with underlying medical conditions or chronic diseases, women who are pregnant or breastfeeding, individuals with a history of eating disorders, or those who have health conditions that affect blood sugar regulation (such as anyone with type 1 or type 2 diabetes or insulin resistance).

A 24-hour water fast also called a 24 hour fast or a 1 day water fast, involves consuming only water and abstaining from all food and caloric beverages for a full 24 hours.

During a 1 day water fast, most people typically drink only plain water, though some people also choose to have seltzer or club soda, herbal tea or caffeinated tea with no added sweeteners, or black coffee. 

Choosing to vary your non-caloric drinks or just stick with plain water is mostly a matter of personal preference as well as how strict you want to be with your water fasting.

The goal is often to eliminate all caffeine to help improve caffeine sensitivity, so most people do choose to avoid caffeinated tea and coffee, even if unsweetened and made with only water.

However, if you do want to have caffeine and prefer coffee to tea, black coffee is still generally permitted when water fasting because it is so low in calories (about 3 calories per cup, or 240 mL) and nutrients that it is not thought to induce metabolic changes that take you out of a state of fasting.1van Dam, R. M., Pasman, W. J., & Verhoef, P. (2004). Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentrations: Randomized controlled trials in healthy volunteers. Diabetes Care27(12), 2990–2992. https://doi.org/10.2337/diacare.27.12.2990

Herbal tea.

How to Do a 24 Hour Water Fast

Actually, doing a 1 day water fast is very straightforward. All you do is abstain from all caloric intake and drink only water for 24 hours.

However, physically and mentally, preparing for the fast itself is important.

Although not mandatory, practicing with some time-restricted intermittent fasting can be helpful before taking on a full 24 hour water fast.

For example, you might consider starting with 14/10 intermittent fasting or 16/8 intermittent fasting, gradually extending your overnight fast as your body gets more accustomed to carrying out your usual routine with no current energy intake.

You can then progress to 20/4 intermittent fasting, where you are fasting for a full 20 hours per day and then confining your caloric intake to just four hours.

Doing these shorter fasting protocols will help you “rehearse” for your 24 hour water fast and will help get your body and mind adjusted to what it feels like to fast for an extended period of time.

A plate a pink clock and utensils.

Benefits of 24 Hour Water Fasting

There are quite a few potential physical and mental health benefits of doing a 24 hour fast periodically, including the following:

Supporting Weight Loss

One of the potential benefits of any type of fasting can potentially help you burn fat, maintain a healthy body weight, and reduce the risk of obesity because you are not consuming calories during the fasting period.

Because you need to generate a caloric deficit to lose weight (at a rate of 3,500 calories per pound of body fat loss), consuming zero calories for a full day can help create a sizeable caloric deficit, as long as you don’t compensate by rebounding with binge eating in your post-fast meals.

Depending on your daily caloric needs and BMR, a 24 hour fast should generate at least half, if not the majority, of the 3,500-calorie deficit you need for one pound of fat loss.

Indeed, evidence suggests that fasting can promote weight loss and induce favorable improvements in body composition. 

For example, a review2Welton, S., Minty, R., O’Driscoll, T., Willms, H., Poirier, D., Madden, S., & Kelly, L. (2020). Intermittent fasting and weight loss. Canadian Family Physician66(2), 117–125. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7021351/ of 27 intermittent fasting dietary interventions found that all 27 studies resulted in weight loss of 0.8% to 13.0% of the starting weight with no serious adverse events. 

Keep in mind that the effectiveness of a 24 hour water fast for weight loss will depend on how often you do it and your overall caloric balance on a larger time scale.

An empty plate and utensils.

Improving Health

Health benefits of water fasting can include fat loss,3Tinsley, G. M., & La Bounty, P. M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition Reviews73(10), 661–674. https://doi.org/10.1093/nutrit/nuv041 reducing oxidative stress and chronic inflammation,4Johnson, J. B., Summer, W., Cutler, R. G., Martin, B., Hyun, D.-H., Dixit, V. D., Pearson, M., Nassar, M., Tellejohan, R., Maudsley, S., Carlson, O., John, S., Laub, D. R., & Mattson, M. P. (2007). Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free Radical Biology and Medicine42(5), 665–674. https://doi.org/10.1016/j.freeradbiomed.2006.12.005 decreasing LDL (“bad”) cholesterol and triglycerides levels,5Bhutani, S., Klempel, M. C., Berger, R. A., & Varady, K. A. (2010). Improvements in Coronary Heart Disease Risk Indicators by Alternate-Day Fasting Involve Adipose Tissue Modulations. Obesity18(11), 2152–2159. https://doi.org/10.1038/oby.2010.54 promoting autophagy (cell cleanup) and cellular health,6Bagherniya, M., Butler, A. E., Barreto, G. E., & Sahebkar, A. (2018). The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Research Reviews47, 183–197. https://doi.org/10.1016/j.arr.2018.08.004 reducing the risk of hypertension (high blood pressure), boosting the secretion of human growth hormone (HGH), improving insulin sensitivity,7Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research164(4), 302–311. https://doi.org/10.1016/j.trsl.2014.05.013 and reducing the risk of cardiovascular disease, heart disease, and Alzheimer’s disease.

8 Tips for a 24 Hour Water Fast

A 24 hour water fast can be really overwhelming and intimidating if you’ve never tried extended fasting, but here are some tips to help support the process:

#1: Speak With Your Doctor

Even short-term water fasting is not necessarily safe, healthy, or optimal for many people, depending on your health status and needs.

For example, those with type 2 diabetes, kidney or heart disease, or who take medication for hypertension (high blood pressure) may have special considerations for fasting.

And, there can be side effects of fasting such as low blood glucose levels (blood sugar levels) due to the lack of carbohydrates, glycogen depletion (which can affect athletic performance, low blood pressure, dehydration, electrolyte imbalances, irritability, and more.

There are often other safer, less extreme alternatives to weight management and health than prolonged fasting.

Having a discussion with your healthcare provider and getting medical supervision will help ensure that a one day water fast is safe for you.

A person drinking a bottle of water.

#2: Drink Water to Prevent Dehydration

Knowing how much water to drink during a water fast is one of the biggest challenges.

Most experts say that you should drink a minimum of 1 to 2 L, although anyone with a larger body size, who lives in a warm climate, or who sweats a lot will need to drink even more water.

#3: Use Electrolytes

Fortifying your water with electrolyte tablets will help ensure that you do not dilute the concentration of your electrolytes, which can induce hyponatremia, a dangerous condition in which sodium levels fall too low.

If you plan to do alternate-day fasting with frequent full-day fasts, you should speak with your healthcare provider about other supplements you may need to manage your overall well-being and prevent nutritional deficiencies.

#4: Be Mindful Of the Foods You Eat After Your Fast

We often focus on doing our best not to eat anything during the entire 24 hour water fast without putting much thought into what we will eat to break the fast

However, it’s important to choose foods that are gentle on the stomach and get your digestive system back into action rather than going gung-ho on a heavy, sugary, fatty, high-caloric meal, which can increase the risk of refeeding syndrome.8Mehanna, H. M., Moledina, J., & Travis, J. (2008). Refeeding syndrome: what it is, and how to prevent and treat it. BMJ336(7659), 1495–1498. https://doi.org/10.1136/bmj.a301

Refeeding syndrome is a dangerous condition that can occur if you eat too much too soon after prolonged fasting.

Bone broth, soups, low-sugar fruits like melon, steamed vegetables, fish, and whole grains like oats and quinoa are some of the best foods to eat after fasting.

A glass of water with electrolyte powder.

#5: Don’t Overeat the Night Before

Heading into a 24 hour water fast, many people assume that they should double down and eat a big meal to keep them satiated through most of the following day. However, make sure to eat easily digestible foods that are nourishing and support overall wellness. 

Processed foods, fatty meats, sugar, and alcohol will all be more difficult to digest and can compromise the benefits of water fasting.

#6: Be Mindful About Exercise

Depending on your overall health status and your experience with fasting, exercising during a 24 hour water fast is typically not ideal because you can’t fuel properly beforehand, and you cannot refuel after to help facilitate recovery unless you time the session at the very end of your fast. 

However, at this point, you’ll be pretty depleted. If you do want to exercise during a 1 day water fast, you should engage in low-intensity exercise such as walking, hiking, yoga, Pilates, or gentle indoor cycling.

A person hunched over tired after running.

#7: Get a Buddy

A 24 hour water fast will test your physical and mental grit. 

Having a buddy who is going through the experience with you can provide social support and motivation to help you through. 

Recruit a family member, friend, coworker, or join an online group if you think that you would like the added accountability (and someone to commiserate with!).

#8: Journal

Keep a journal of your symptoms and experiences. If you end up wanting to make a 24 hour water fast a routine part of your lifestyle, you can use tips and memories from previous experiences to inform each subsequent iteration for continued success.

Although doing a 24 hour water fast isn’t necessarily safe or tenable for everyone, it can be a helpful way to boost health and support weight loss goals for others.

For more detailed information on what to do when you finish your fast, take a look at our article, Here Are The 10 Best Foods To Break A Fast.

A person journaling.

References

  • 1
    van Dam, R. M., Pasman, W. J., & Verhoef, P. (2004). Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentrations: Randomized controlled trials in healthy volunteers. Diabetes Care27(12), 2990–2992. https://doi.org/10.2337/diacare.27.12.2990
  • 2
    Welton, S., Minty, R., O’Driscoll, T., Willms, H., Poirier, D., Madden, S., & Kelly, L. (2020). Intermittent fasting and weight loss. Canadian Family Physician66(2), 117–125. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7021351/
  • 3
    Tinsley, G. M., & La Bounty, P. M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition Reviews73(10), 661–674. https://doi.org/10.1093/nutrit/nuv041
  • 4
    Johnson, J. B., Summer, W., Cutler, R. G., Martin, B., Hyun, D.-H., Dixit, V. D., Pearson, M., Nassar, M., Tellejohan, R., Maudsley, S., Carlson, O., John, S., Laub, D. R., & Mattson, M. P. (2007). Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free Radical Biology and Medicine42(5), 665–674. https://doi.org/10.1016/j.freeradbiomed.2006.12.005
  • 5
    Bhutani, S., Klempel, M. C., Berger, R. A., & Varady, K. A. (2010). Improvements in Coronary Heart Disease Risk Indicators by Alternate-Day Fasting Involve Adipose Tissue Modulations. Obesity18(11), 2152–2159. https://doi.org/10.1038/oby.2010.54
  • 6
    Bagherniya, M., Butler, A. E., Barreto, G. E., & Sahebkar, A. (2018). The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Research Reviews47, 183–197. https://doi.org/10.1016/j.arr.2018.08.004
  • 7
    Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research164(4), 302–311. https://doi.org/10.1016/j.trsl.2014.05.013
  • 8
    Mehanna, H. M., Moledina, J., & Travis, J. (2008). Refeeding syndrome: what it is, and how to prevent and treat it. BMJ336(7659), 1495–1498. https://doi.org/10.1136/bmj.a301
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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