BlogWeight LossWater Fasting: Pros, Cons, and How to Do It Right

Water Fasting: Pros, Cons, and How to Do It Right

10 mins read
Mariia Roza
Written by Mariia Roza on October 08, 2021
Ievgeniia Dobrynina
Fact checked by Ievgeniia Dobrynina
The Unimeal team works to give you the most accurate and up-to-date information. All texts are reviewed by a panel of experts and editors and updated according to the latest research. Only evidenced-based and verified sources of leading medical publications and universities get into the article materials.
Dr. Olena Avdiievska, MD, RDN
Medically reviewed by Dr. Olena Avdiievska, MD, RDN
Unimeal provides articles with trustworthy and experts-proved information. Our health content is reviewed by professional nutritionists and trainers to extract for users the most verified and medically checked data.

Some people think fasting is a sustainable strategy for weight loss. Other people think it might take you into the vicious cycle of restrictions and binges. What do you think of it? A trendy fad diet, snake oil, or a magic pill against all illnesses? Let's find out together!

Table of content

Warning: Our biggest concern about prolonged fasting is that people often use it as a quick fix for weight loss or after massive overeating. If these are your motives to try water fasting, just know that this is not the solution! So, please, if you’re prone to binge eating, if you tend to overeat, or if you have any disruptive eating habits, don’t use fasting for weight loss.

Get your 100% personalized meal plan by completing our 3-min quiz

Get your 100% personalized meal plan by completing our 3-min quiz

None of the known diets should be followed without considering your unique body needs, preferences, and goals

Start Quiz

Another thing you should consider is that water fasting is not for everyone. For example, it might do more harm than good to people with diabetes and low blood pressure. It is surely not recommended to pregnant women, children, and people who have had or still have eating disorders. Fasting is prohibited for people with kidney stones or renal insufficiency. The only person who can tell if you will benefit from prolonged water fasting is your health provider. Consult your doctor before trying prolonged water fast.

What is water fasting?

Fasting is basically when you refrain from any food whatsoever. There are some variations, though. In some cases, you’re allowed to drink black coffee with no additives. In some cases, you’re recommended to add salt and minerals to your water to prevent electrolytes imbalance. Some people eliminate water and do the so-called dry-fasting. We’re going to talk about water fasting, where you can drink only water with no non-caloric beverages like black coffee and tea.

This is how your meals look when you follow water fasting
This is how your meals look when you follow water fasting

Intermittent fasting

The most widespread type of fasting that everyone heard of is intermittent fasting. It is claimed to lead to autophagy which can have multiple benefits for health, including decreasing risks of certain diseases, like cancer and Alzheimer’s disease.

These schemes of intermittent fasting are the most popular:

  • 14:10 protocol is a relatively new approach to intermittent fasting that states you can still get positive results, including weight loss if you eat all your meals in ten hours and fast for another 14 hours.
  • 16:8 intermittent fasting protocol is the most popular one. According to this approach, you can eat for eight hours and fast for 16 hours of the day.
  • The warrior diet or the 20:4 scheme. You eat for four hours and fast for the rest of the day.
  • OMAD is an acronym for one-meal-a-day. Basically, you fast for 23 hours and have a one-hour eating window.
  • Alternate day fasting. Eat every other day and fast the rest of the days.
  • 5:2 intermittent fasting means that you eat as you usually do for five days of the week and fast or eat no more than 25% of your calories for another two consecutive days a week. 

Short-term fasting

24 to 72 hours without food are considered short-term fasting protocols. It undoubtedly boosts weight loss as, during these hours, your body doesn’t get energy from food and is forced to use glycogen stores as its primary fuel source. If you don't have enough glycogen in the muscles, your body will switch to muscles and fat tissue.

Long-term fasting

That can be a 5-day, 2-week, or even 40-day fasting. People usually opt for these fasting protocols to lose weight really quickly. Most long-term fasting protocols should always be conducted under medical supervision.

Religious fasting

Most religions have some kind of food restrictions happening throughout the year. These include dawn to dusk fasting during the holy month of Ramadan, Great Fast in Christianity when a person should become spiritually stronger. There are also fasting periods in Judaism and Catholicism. People might refrain from some food groups (usually animal products) or food entirely during these periods. 

Fasting before the medical interruption or surgery

If you’re about to have anesthesia before the medical interruption, you might be required to refrain from food and sometimes beverages for 4-12 hours before your surgery. This period may vary depending on the kind of medical treatment you will have and even the country where you’re about to get surgery.

How to fast safely?

The main problem with fasting for prolonged periods is that not much research is conducted on the topic. For that reason, almost all recommendations you will find online are “bro-science” that relies on anecdotal evidence and has no science behind it. The harsh truth is that only your doctor can tell you how to start and end your fasting. Before starting your 72-hour fast, try the 36-hour fasting protocol to ensure that this eating pattern fits you.

These are some thoughts on starting and ending up fasting that sound legit.

A week before the fast

Minimize toxic substances abuse. If you used to drink a glass of wine or a pint of beer every evening, two weeks before the fast is the perfect time to limit spirits consumption. That’s because you will feel deprived during your first days of fasting, and you don’t need to add withdrawal symptoms to your struggle. If you want to make water fast, with no coffee or tea, it is also better to refrain from caffeine a week before your fast begins.

Eliminate some food groups gradually. Some keto-followers say that you should try keto protocols before you start fasting. Some vegans say that you should opt for veganism a day or two before the prolonged fast. The problem is there is no scientific evidence that one approach is better than the other. So, let’s keep to the basics, shall we?

Decrease your meat and legume portions a week or two before the fasting period. You can also minimize the amount of highly palatable foods rich in fats and sugars in your diet, so you don’t have withdrawal and crave them less while fasting.

Control your portion sizes. There is no solid scientific evidence that the stomach becomes larger when you eat large portions or that it shrinks when you start eating less food. However, some research shows that the stomach capacity of obese people reduces after dieting. This means when you eat smaller portions, your stomach gets used to sending signals of being full to your brain when it has less food inside. Of course, during the fast, it will still be telling you (with all tools available) that it’s empty, but maybe, if you eat smaller portions a week or two before the fast, the fast itself will be easier to handle.

A day before the fast

Get ready for the side effects. You will crave food and will have less energy than on regular days.

Decrease your calories. Eating a bit less a day or two before the fast might make your experience less difficult. You should also opt for fruits, vegetables, and other easily digestible foods just before your fast starts.

Eat more salt and drink more water. As a rule, some sodium and electrolytes intake is recommended during prolonged fasts, but you can add salt to your water even when you’re on 72-hour water fast. If you don’t want to eat salt while fasting, eat a bit more of it a day or two before you refrain from food.

A diet after water fasting

If you want to maintain your weight loss results after water fasting, you should follow these two rules. 

A bowl of vegetable soup, a great meal to break your fast
A bowl of vegetable soup, a great meal to break your fast

Avoid the refeeding syndrome. Refeeding syndrome is one of the most dangerous things that can happen if you don’t get off your long fast the right way. This metabolic condition occurs because of the shifts in electrolytes and fluids that are possible after malnutrition. How to avoid it? Introduce foods slowly to your diet after fasting. Start with small amounts of vegetables, broths, or vegetable smoothies, and don’t end your fast with a massive meal of hard-to-digest foods.

Don’t binge. Easier said than done. The thing is, fasting can increase the risks of binge eating disorder development which was proved by a 5-year prospective study on 496 adolescent girls. This is why fasting is prohibited for people with ED. That is also why you shouldn’t try it if you tend to overeat or binge eat.

Summing up: Remember about the post-fast recovery, and don’t eat massive amounts of foods right after your fast is over.

How to make fasting easier?

Food is all around us. We socialize around food; we have it at homes, offices, on the streets, on our social media feeds. It’s just a part of our lives. That is why fasting might be so hard. You’re surrounded by something you desperately want but what you’re not allowed to have. Here are some tips on how you can make your fasting experience a bit more bearable. 

Keep yourself busy. This is the most important and very underrated tool of sticking to your fast or basically any restrictive diet. When you’re hungry, you keep thinking about food, so the only way to help yourself is by distracting your thoughts from food. Walking in the woods, reading an exciting book, playing video games… do whatever helps you stay busy.

A person reads a book, trying to keep oneself busy and don't think about food
A person reads a book, trying to keep oneself busy and don't think about food

Sleep more. You will have less energy during the fast, so it’s better to compensate for the lack of calories by sleeping more. Get at least eight hours of sleep every night and allow yourself daytime naps whenever you need them.

Drink more water. This will not only make your fast easier. Drinking water is also necessary to keep you hydrated. When we eat a normal diet, we get part of the liquid from food. This means to stay hydrated while fasting, you should consider the lack of food in your life and increase water consumption.

Don’t plan anything physically challenging. Some people promoting fasting will say that you should take at least brisk walks during fasting. However, you’d better avoid hard physical labor, intensive workouts, and in case you have dizziness and lack of energy, operating machinery or even driving a car.

What are the possible benefits of water fasting?

The most frustrating part about the possible benefits of prolonged fasting is that not much research is conducted on the topic. Most papers state that research on prolonged fasting is limited and is not enough to make conclusions. Another disadvantage of scientific knowledge on fasting is that most experiments were conducted on rodents, not on people.

Because of this lack of evidence, we’re talking about possible benefits that might happen to your body after prolonged fasting.

Water fasting can help with normalizing blood pressure

One study on 1610 individuals has shown that prolonged fasting of 4 to 41 days has decreased blood pressure in people with elevated blood pressure. As more and more research is conducted on the link between fasting and hypertension, it seems like fasting might become a working strategy in treating high blood pressure. 

If you’re not ready to try fasting for your hypertension, you can opt for less drastic methods, like a DASH diet.

Fasting might boost metabolism

This sounds counterintuitive, but one study has shown the rise of the resting energy expenditure among fasting individuals during the first days of their 84-hour fast. It should be noted that the research has been conducted on 11 (not that much) healthy and lean individuals.

Fasting might help in treating cancer

The overview of multiple papers shows that short-term fasting might increase the efficiency of chemotherapy in humans. However, even this extensive survey states that more research should be conducted to make firm conclusions.

Fasting helps lose weight

As during calorie restriction your body starts using its own resources, including fat tissue, fasting is a great tool to lose weight. However, you should understand that fasting is not a magic pill. Studies show no significant difference in weight loss among people who restrict calories and those who opt for short-term intermittent fasting.

Fasting might improve cognitive function

According to a 3-year progressive study, intermittent fasting can enhance cognitive function in older individuals. Another research of 48-hour fasting showed that this eating pattern could improve cognitive functions, like mental flexibility and task switching.

What side effects might water fasting have?

The problem with the “I did my research” approach of those who start a new trendy diet is that it’s very easy to find articles, case studies, and even research proving you right. When you do your research, Google not only “fasting benefits.” Try out “dangers of fasting” as well to get all the spectrum of information, not only the one that proves you right. 

These are just some of the side effects you might notice during the fast:

  • Mood swings. You might become “hangry” and irritable. You might start to pity yourself and dive into melancholy. Fasting is massive physical stress for your body, and your organism will react to it by messing up your emotional state.
  • Food cravings and Array. Of course, you will crave food during the fast. But what’s more dangerous is that you might overeat and binge when you break your fast. 
  • Bad breath. Bad breath happens when you reach full ketosis and when your body starts using your body fat as fuel. This state might not come as quickly as in three days, though.
  • Headaches. There might be multiple reasons behind your headache during the fast. It can happen due to the withdrawal from coffee or sugar, dehydration, too low blood pressure, and even bile intoxication. 
  • Dehydration. If you don’t add salt to your water while fasting, you might face dehydration, even though you drink a gallon of water a day. 
  • Sleep problems. Some people state that they sleep better when fasting, and some state that they can’t sleep on an empty stomach. Be ready for both.
  • Low energy. Almost 15% of people who fasted for 8 weeks using the alternate-day fasting protocol reported general weakness and loss of energy
  • Dizziness. When we fast, our blood sugar falls, and one of its symptoms is dizziness. Dizziness can also be the result of low blood pressure or dehydration.
  • Lower testosterone levels. According to studies, even a short-term fast can decrease testosterone and reproductive hormones. However, their levels get back to the baseline the next day after fasting. 
  • Slower metabolism. When you fast, your body adapts and stops using as much energy as it used to. You fidget less, so your non-exercise activity thermogenesis falls. You don’t eat food, so your thermic effect of food drops. You’re unlikely to work out, so your exercise activity thermogenesis decreases. The most frustrating part is that your body might start using less energy for everyday functioning, which means that your basal metabolic rate will decrease as well. These changes will reverse quickly after refeeding.
A sleeping woman: Fasting can significantly decrees your energy level
A sleeping woman: Fasting can significantly decrees your energy level

The good news is that you can avoid part of these side effects by drinking more liquid and adding 0.5-1 teaspoon of salt a day to your water. 

Signs to stop water fasting

During your first days of fasting, you might experience dizziness, constipation, nausea, headache, fatigue, etc. These might be the symptoms of the so-called keto-flu. If you add electrolytes to your water, you can avoid almost all these side effects. 

Should you stop your water fast if you experience these conditions? It depends on your goals and on what your health provider says.

Along with these side effects of short-term fasting, there might be some more severe consequences for your health if you opt for long-term fasting. You can face malnutrition and vitamins and minerals deficiency. This is why we insist that you do long-term fasting only under medical supervision. We’re all different, and if your neighbor was okay with fasting for 40 days, it doesn’t mean that your body is capable of coming through such a challenging diet with no adverse consequences.

Consult your doctor before you start fasting, and don’t hesitate to call him or her if you feel bad without food.

Does fasting help lose water weight? 

Fasting is something lead actors do before a major scene where they have to show off muscles. Bodybuilders also use this tool before a competition, as well as professional athletes, like wrestlers, before the weight-in. By doing so, they decrease the amount of water in their body to fit in a weight category or make their muscles look as lean as possible. 

You can use a 3-day fast to look your absolute best if this is something critical, like a national competition, world championship, or an acting scene in a million-dollar movie. But maybe, if the stakes are not that high, it’s better to opt for less drastic changes to your diet? For example, to get rid of excess water weight, you can decrease the carbs and salt in your diet several days before the important event.

Water fast results 

You will surely lose weight. Part of it will be from fat and muscles, but the largest part of lost weight will be from water, and you will regain it quickly once you start eating again. The weight loss results may vary and depend on your initial body weight. The more you weigh, the more pounds you will lose on fasting.

A woman's weight loss results after water fasting
A woman's weight loss results after water fasting

You might end up with disordered eating. If your only motivation for doing a short-term fast is weight loss, the chances are, this quick fix will do more harm than good to your weight loss journey. After the period of severe restriction, your ghrelin levels might skyrocket, and you will overeat several times to several days after you break your fast. You should understand that this is not because you lack willpower, it’s just how your body works!

Another possible consequence of a fast is that you might want to do it longer than you’ve planned. The thing is, during the prolonged fasting periods, ghrelin levels may decrease, making you more comfortable with not eating. Anecdotal evidence state that after the third day of fasting, people experience the so-called “fasting high,” when they feel extremely good, energetic, and light. If you’re prone to or used to have restrictive types of disordered eating, fasting might trigger your ED.

You might see positive effects on your health. Fasting does have some not thoroughly researched beneficial impact on your health. You can normalize your blood pressure and blood sugar levels. It is possible that you will get a better mental focus and will be able to deal with complex tasks easier. And maybe not. There is not enough data on the positive effects of fasting on human beings.

Your tastebuds will be reloaded. After a prolonged period of fasting, you will taste food differently. You might find that your favorite desserts are now too sweet, and vegetables are not that blank. Fasting will surely help you decrease the amount of sugar and flavorings you use on a daily basis.

FAQ on water fasting

Here are some answers to the most frequent questions on water fasting. We hope they will work as a conclusion to our article on fasting.

Does fasting help lose weight?

There are multiple reasons why people want to fast, but the most common one is weight loss. You can find thousands of people who’ve lost weight by doing prolonged fasting. It just doesn’t mean that this is THE best or THE healthiest way to lose weight. Always consult your doctor before you try something as drastic as water fasting.

How much weight can you expect to lose during fasting? 

It all depends on multiple factors, like your baseline weight, what kind of diet you were following before the fast, your body fat percentage, your level of hydration, and even your menstrual cycle if you’re a female. The average weight loss after three days of fasting is five pounds. The higher BMR you have, the more weight you lose during fasting. Keep in mind that weight loss doesn’t equal fat loss. Most of the weight you will lose during your first days without food will be from water, including the water in your muscles, which means that they won't look as pumped as they used to.

How to deal with hunger while water fasting?

Hunger is the most challenging part of fasting. If you do long-term fasting under medical supervision, your doctor might give you some particular recommendations on making fasting easier. For example, they can prescribe bile diversion. However, the latter procedure should only be done by medical professionals and under medical supervision.

If you want to fast for up to 72 hours at home, the most efficient thing that will help you is keeping away from the fridge and food. Keep yourself busy and don’t get into challenging situations, like dining with friends in your favorite restaurant. Drink whenever you want to eat and stay motivated.

What to eat after water fasting for 7 days?

When you fast for a long time, you should be careful with reintroducing food into your life; otherwise, you can experience symptoms of refeeding syndrome. These symptoms might include salt and water retention, high blood pressure, edema, seizure, and even heart failure. They usually occur during the first 72 hours of the replenishing phase.

To avoid this metabolic state, break your fast the right way:

  • Start with eating cooked fruits and vegetables.
  • Eat in small portions.
  • Get back to your maintenance calorie intake in no less than 5 days.
  • Don’t make your first day after prolonged fasting the “cheat day”!
  • Avoid carbs with a high glycemic index to prevent spikes of insulin. 
  • Don’t eat products rich in saturated fats during the first days after fasting so that your digesting system can adapt to receiving food again. 

If you feel bad after eating or see any symptoms of refeeding syndrome, don’t hesitate to call your doctor!

How do you feel about my article?

Unimeal does not diagnose or suggest treatments. Any description of the diet, training plan or supplement should be discussed with your current physician or nutritionist. This article does not address specific conditions and is simply meant to provide general information on healthcare topics. Following any advice is at your own initiative and does not impose any responsibility on the blog authors for your health and safety.



By choosing high-quality sources, we make sure that all articles on the Unimeal blog are reliable and trustworthy. Learn more about our editorial processes.

Levine B., Kroemer G. (2008, January 11). Autophagy in the Pathogenesis of Disease. Cell. DOI:10.1016/j.cell.2007.12.018
Mah L. Y., Ryan K. M. (2012, January). Autophagy and Cancer. Coldspring Harbor Perspectives in Biology. DOI:10.1101/cshperspect.a008821
Zare-shahabadi A., Masliah E., Johnson G. V. W., et al. (2016, September 27). Autophagy in Alzheimer’s Disease. Reviews in the Neurosciences. DOI:10.1515/revneuro-2014-0076
Geliebter A., Schachter S., Lohmann-Walter C., et al. (1996, February). Reduced Stomach Capacity in Obese Subjects After Dieting. The American Journal of Clinical Nutrition. DOI:10.1093/ajcn/63.2.170
Mehanna H. M., Moledina J., Travis J. (2008, June 28). Refeeding Syndrome: What It Is, and How to Prevent and Treat It. BMJ. DOI:10.1136/bmj.a301
Stice E., Davis K., Miller N. P., et al. (2008, November). Fasting Increases Risk for Onset of Binge Eating and Bulimic Pathology: A 5-Year Prospective Study. Journal of Abnormal Psychology. DOI:10.1037/a0013644
Guelinckx I., Tavoularis G., Konig J., et al. (2016, October). Contribution of Water from Food and Fluids to Total Water Intake: Analysis of a French and UK Population Surveys. Nutrients. DOI:10.3390/nu8100630
Grundler F., Mesnage R., Michalsen A., et al. (2020, November 23). Blood Pressure Changes in 1610 Subjects With and Without Antihypertensive Medication During Long‐Term Fasting. Journal of the American Heart Association. DOI:10.1161/JAHA.120.018649
Goldhamer A., Lisle D., Paria B., et al. (2001, June). Medically Supervised Water-Only Fasting in the Treatment of Hypertension. Journal of Manipulative and Physiological Therapeutics. DOI:10.1067/mmt.2001.115263
Zauner C., Schneeweiss B., Kranz A., et al. (2000, June). Resting Energy Expenditure in Short-Term Starvation Is Increased as a Result of an Increase in Serum Norepinephrine. The American Journal of Clinical Nutrition. DOI:10.1093/ajcn/71.6.1511
De Groot S., Pijl H., van der Hoeven J. J. M., et al. (2019, May 22). Effects of Short-Term Fasting on Cancer Treatment. Journal of Experimental and Clinical Cancer Research. DOI:10.1186/s13046-019-1189-9
Varady K. A. (2011, July). Intermittent Versus Daily Calorie Restriction: Which Diet Regimen Is More Effective for Weight Loss? Obesity Reviews: An Official Journal of the International Association for the Study of Obesity. DOI:10.1111/j.1467-789X.2011.00873.x
Ooi T. C., Meramat A., Rajab N. F., et al. (2020, September). Intermittent Fasting Enhanced the Cognitive Function in Older Adults with Mild Cognitive Impairment by Inducing Biochemical and Metabolic changes: A 3-Year Progressive Study. Nutrients. DOI:10.3390/nu12092644
Solianik R., Sujeta A., Terentjevienė A., et al. (2016, November). Effect of 48 h Fasting on Autonomic Function, Brain Activity, Cognition, and Mood in Amateur Weight Lifters. BioMed Research International. DOI:10.1155/2016/1503956
Watkins E., Serpell L. (2016, August). The Psychological Effects of Short-Term Fasting in Healthy Women. Frontiers in Nutrition. DOI:10.3389/fnut.2016.00027
Musa-Veloso K., Likhodii S. S., Cunnane S. C. (2002, July). Breath Acetone Is a Reliable Indicator of Ketosis in Adults Consuming Ketogenic Meals. The American Journal of Clinical Nutrition. DOI:10.1093/ajcn/76.1.65
Torelli P., Manzoni G. C. (2010, August). Fasting Headache. Current Pain and Headache Reports. DOI:10.1007/s11916-010-0119-5
Juliano L. M., Griffits R. R. (2004, October). A Critical Review of Caffeine Withdrawal: Empirical Validation of Symptoms and Signs, Incidence, Severity, and Associated Features. Psychopharmacology. DOI:10.1007/s00213-004-2000-x
Campbell N. R., Wickert W., Magner P., et al. (1994, December). Dehydration during fasting increases serum lipids and lipoproteins. Clinical and Investigative Medicine. PMID:7895421
Michalsen A., Schlegel F., Rodenbeck A., et al. (2003). Effects of Short-Term Modified Fasting on Sleep Patterns and Daytime Vigilance in Non-obese Subjects: Results of a Pilot Study. Annals of Nutrition and Metabolism. DOI:10.1159/000070485
Hoddy K. K., Kroeger C. M., Trepanowski J. F. (2015, May). Safety of Alternate Day Fasting and Effect on Disordered Eating Behaviors. Nutrition Journal. DOI:10.1186/s12937-015-0029-9
Klibanski A., Beitins I. Z., Badger T., et al. (1981, August). Reproductive Function During Fasting in Men. The Journal of Clinical Endocrinology and Metabolism. DOI:10.1210/jcem-53-2-258
Hall K. D. (2018, May). Metabolic Adaptation to Weight Loss. Obesity (Silver Spring). DOI:10.1002/oby.22189
Bostock E. C. S., Kirkby K. C., Taylor B. V., et al. (2020, March). Consumer Reports of “Keto Flu” Associated with the Ketogenic Diet. Frontiers in Nutrition. DOI:10.3389/fnut.2020.00020
Natalucci G., Riedl S., Gleiss A., et al. (2005, June). Spontaneous 24-h Ghrelin Secretion Pattern in Fasting Subjects: Maintenance of a Meal-Related Pattern. European Journal of Endocrinology. DOI:10.1530/eje.1.01919
Reber E., Friedly N., Vasiloglou M. F., et al. (2019, December). Management of Refeeding Syndrome in Medical Inpatients. Journal of Clinical Medicine. DOI:10.3390/jcm8122202