BlogWeight LossWater Fasting for 3 Days: Pros, Cons, and How to Do It Right

Water Fasting for 3 Days: Pros, Cons, and How to Do It Right

A trendy fad diet, snake oil, or a magic pill against all illnesses? Let’s find out together!

Mariia Roza
Written by Mariia Roza on October 08, 2021
Fact checked by Ievgeniia Dobrynina

Table of contents

Warning: My 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! Fasting is not a sustainable strategy for weight loss. It might take you into the vicious cycle of restrictions and binges. 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.

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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 used to have 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 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. What we’re going to talk about here is water fasting, where you can drink only water and non-caloric beverages like black coffee and tea for 72 hours.

Why do people fast?

These are some of the most common reasons why people choose short-term or prolonged water fasting.

Because of religious reasons

Most religions have some kind of food or food groups 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. During these periods, people might refrain from some food groups (usually animal products) or from food entirely. 

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 time period may vary depending on the kind of medical treatment you’re going to have and even the country where you’re about to get surgery.

To get health benefits 

Intermittent fasting and prolonged fasting are claimed to lead to autophagy(1) which can have multiple benefits for health, including decreasing risks of certain diseases, including cancer(2) and Alzheimer’s disease(3).

Because this is what our ancestors used to do

Almost all fasting-promoting articles and videos start with the statement that “people were fasting for long periods since the beginning of times!” And this is where some of us might get into a cognitive bias, like, “maybe this is what we should do too!” 

Before you get to this conclusion, just think of how much has the life expectancy increased compared to the Stone age. Might this be partly due to the fact that more food is now available to people all over the world? Not everything our ancestors used to do is better. 

To “detox” the body

Though we know that liver is a perfect tool to clean our bodies from toxins, some people still think that it needs help and try to provide it by prolonged fasting periods.

For fast weight loss

This is the most common reason why people try 3-day fasting. It surely boosts weight loss as during 72 hours your body doesn’t get energy from food and is forced to use glycogen stores as its primary source of fuel. If you don't have enough glycogen in muscles, your body might switch to muscles and fat tissue.

How to fast safely?

The main problem with fasting for prolonged periods is that there is not that much research 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 you should start and end your fasting. Before you start your 72-hour fast, try the 36-hour fasting protocol, to make sure 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. There are keto-followers who say that you should try keto protocols before you start fasting. There are vegans who 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 strong 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(4) shows that the stomach capacity of obese people reduces after dieting. This means, when you eat smaller portions, your stomach gets used to send 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 normal 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.

After the fast

Avoid the refeeding syndrome. Refeeding syndrome(5) is one of the most dangerous things that can happen if you don’t get off your prolonged fast the right way. This is a metabolic condition that happens 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(6) on 496 adolescent girls. This is why fasting is prohibited for people with ED. This is why you shouldn’t try it if you have a tendency to overeating or binge eating.

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 how you can 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.

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(7) 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.

How much weight will I lose on a 3-day water fast?

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 will lose during fasting. Keep in mind that weight loss doesn’t equal fat loss. Most of the weight you will lose will be from water, including the water in your muscles, which means that they won't look as pump as they used to.

What are the possible benefits of a 3-day water fast?

The most frustrating part about the possible benefits of prolonged fasting is that there is not that much research 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(8) 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(9) 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, for example.

Fasting might boost metabolism

This sounds counterintuitive, but one study(10) 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(11) of multiple papers shows that short-term fasting might increase the efficiency of chemotherapy in humans. However, even this vast survey states that more research should be conducted to make strong conclusions.

Fasting helps lose weight

As your body starts using its own resources, including fat tissue, to keep you going, fasting is one of the tools to lose weight. However, what you should understand is that fasting is not a magic pill. Studies(12) 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(13), intermittent fasting can enhance cognitive function in older individuals. Another research(14) of 48-hour fasting showed that this eating pattern can improve some cognitive functions, like mental flexibility and task switching. There is not enough data linking 72-hour fasting protocols with cognitive function.

What side effects you should expect during your 72-hour fast?

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 you would like to read. 

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 it will react to it by messing up your emotional state.
  • Food cravings and binge episodes. Of course, you will crave food during the fast. But what’s more dangerous is that you might overeat and binge during refeeding. 
  • Bad breath. Bad breath happens(15) when you reach full ketosis, aka when your body starts using your body fat as fuel. This state might not come as quickly as in three days, though.
  • Low energy. As your metabolism might slow down during the fast, you can experience a loss of energy. 
  • Headaches. There might be multiple reasons behind your headache during the fast. It can happen due to the withdrawal from coffee(16) 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.
  • 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(17), even a short-term fast can decrease the levels of testosterone and reproductive hormones. However, these 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.

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.

Another way how you can make your fasting more enjoyable is by bile diversion which is recommended during prolonged fasting. However, the latter procedure should only be done by medical professionals and under medical supervision.

Fasting to lose water weight 

Fasting is something lead actors do before a major scene where they have to show off muscles. This is also a tool bodybuilders use before a competition or professional athlete, like wrestlers, before the weight-in. By doing so, they decrease the amount of water in their body so they can 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 very quickly once you start eating again. The weight loss results may vary and will highly depend on your initial body weight. The more you weigh, the more pounds you will lose on fasting.

You might end up with disordered eating. If your only motivation for doing a 3-day fast is weight loss, the chances are, this quick fix will make 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 our bodies work!

Another possible consequence of a 3-day fast is that you might want to do it longer than you’ve planned. The thing is, during the prolonged fasting periods, ghrelin(18) 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 fully researched beneficial effects 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 difficult 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 that vegetables are not that blank. Fasting will surely help you decrease the amount of sugar and flavorings you use on a daily basis.

Summing up

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 72-hour fasting.


  • 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.
  • 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
  • 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
  • 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
  • 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
  • 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