Intermittent fasting has been all the rage, but have you heard of its slightly more intense cousin, water fasting? Water fasting is a method the Waterboy would truly approve of since it involves drinking only water while fasting.

Although this type of fasting can be difficult (because what is a life without snacks and coffee?), it has several potential benefits. But, water fasting also isn’t perfect and does come with some risks.

Let’s look at what it takes to water-fast and the benefits and downsides of drinking only high quality H2O.

Water fasting, as the name suggests, involves fasting (i.e., no food) and drinking only water for a period of time (no zero-calorie drinks, either).

Water fasting is similar to some forms of intermittent fasting (IF). IF often involves setting a large window of time in which you don’t eat. This could be several hours a day or up to 36 hours at a time. Alternate-day fasting is a form of IF that involves fasting every other day. A water fast can last anywhere from 1 to 3 days, but it, too, can vary.

One difference between IF and water fasting is that fasting gurus typically agree black coffee, tea, and bone broth are totally fine during IF, whereas all three are no-gos for water fasters.

The line between IF and water fasting is blurry. Water fasting is often suggested for medical purposes, and IF is championed for weight loss and health benefits. But water fasting can have many of the same weight loss and health effects as IF. Someone who is intermittent fasting could also be water fasting if they only drink H2O.

Who is water fasting for?

Before you start any program involving prolonged fasts, make sure to consult your doctor. People may water-fast for a variety of reasons, including:

  • health benefits
  • medical procedure preparation
  • religious observations or spiritual reasons
  • autophagy (basically your body’s cell recycling center unlocked by fasting)

The internet will also tell you water fasts can be used for weight loss, which is true. However, this isn’t the most sustainable weight management option for most people. Incorporating IF into your routine would be a more beneficial way to use fasting for weight loss.

Who should avoid it

Most healthy people can do a water fast with no significant complications, but there are some people who should avoid it or who should complete a fast only with close medical supervision:

  • People on blood pressure medications. Prolonged periods of fasting can sometimes be associated with dehydration and lower blood pressure. Dangerously low blood pressure levels could occur in people who are also taking medications to lower their blood pressure.
  • People with diabetes. If you’re on insulin or medications to regulate blood sugar, abruptly stopping your food intake can also put you at risk of low blood sugar, which can be serious. It can also be more difficult for people with diabetes to manage their blood sugar levels while fasting even if they aren’t on insulin or other meds.
  • People who are pregnant or breastfeeding. Water fasting could prevent you from getting all the nutrients your body needs to keep you and baby healthy.
  • People with a history of disordered eating. Water fasting is a pretty extreme regimen and may exacerbate disordered eating patterns.

How long it should last

Typically, water fasts last anywhere from 24 hours to 3 days, but that can vary if you’re following more of an IF routine. Generally, extended fasts without medical supervision are not recommended — especially if you have any preexisting conditions.

Additionally, you probably shouldn’t water-fast for a long period more than once or twice per month. Water fasting too often can deprive your body of vital nutrients that it can only get from food.

What to expect when you’re water fasting

Well, you’ll probably get hungry. But don’t worry — your body will adapt with time. You’ll also want to pay attention to how much water you’re drinking. You will rapidly lose some fluid as your body burns through its carbohydrate stores, so make sure to drink up.

Some of the changes in your body may make you have to pee A LOT, especially early in your fast and if you’re drinking more water than usual.

You may experience some side effects while fasting, including:

  • hunger
  • excessive thirst
  • fatigue
  • muscle cramps (especially at night)
  • headaches

If you’ve fasted before, it might be easier for you to water-fast than it is for those with little fasting experience.

When it’s time to quit

If you start feeling nauseated or lightheaded, you should stop your fast immediately. You should also look out for signs of an electrolyte imbalance, including fatigue, headache, and nighttime leg cramps.

What to do after your fast

Although you will really want to do this after a water fast, diving into a large or heavy meal isn’t the best idea.

In extreme cases, this could lead to refeeding syndrome, which occurs when there are rapid shifts in fluid and electrolytes in your body. This can cause severe, debilitating symptoms like fatigue, confusion, seizures, and heart failure — particularly if you had a longer water fast.

Consuming a large, high-calorie meal after a water fast could be counterproductive for your health. It’s best to break your fast with a small meal or snack. If you fasted for a prolonged period, it may be best to gradually increase the size of your meals back to normal over the next 1 to 3 days.

Water fasting does have some potential benefits, which may be why it’s been a thing for thousands of years.

Unfortunately, there’s not a ton of research on pure water fasting, but we can look at some of the many studies that have been done on IF and other types of fasting to get some insight.


Autophagy sounds like a villain in “Osmosis Jones,” but it’s actually a process triggered by fasting that helps your body recycle old and unused parts of cells. It may have some therapeutic benefits for people with cancer and Alzheimer’s disease.

Lower blood pressure

Research on other fasting regimens has shown fasting can improve blood pressure. This includes studies that have looked at 300-calorie liquid diets (which are similar to fasting) and fasting during Ramadan, a monthlong period when Muslims fast from sunrise to sunset.

Blood sugar management

According to a 2018 study, intensive fasting may help people with type 2 diabetes improve their blood sugar levels and potentially eliminate the need for insulin and other diabetes medications.

However, if you have diabetes, you need to get your healthcare team on board before you start fasting, because there are risks.

Regulation of hunger hormones

Fasting may help regulate your levels of leptin, a hormone that controls your fullness. Leptin resistance is legit a thing, and it can keep you from feeling satisfied with what and how much you eat.

While some studies have shown fasting can influence leptin, the exact effects of fasting on leptin sensitivity aren’t clear.

Improved cholesterol levels

Fasting may improve your cholesterol levels, potentially decreasing your risk of heart disease.

Specifically, it may increase your high-density lipoprotein (HDL) cholesterol while decreasing your triglyceride levels — both very good things. HDL-triglyceride ratio also may be an indicator of heart disease and type 2 diabetes risk.

Better liver function

Fasting can help your body burn through stored fat, including the harmful fat that can build up on your liver and impede its function. One study found that Ramadan fasting may help improve fatty liver disease.

Cancer treatment

A 2018 study found that fasting may starve tumor cells while helping to protect noncancerous cells from traditional cancer treatments like radiation and chemotherapy.

This could help keep the body stronger during treatment, resulting in fewer side effects. But more research is needed to verify the link.

Surgery prep

Ever wonder why you’re told to fast before medical procedures and blood tests?

Certain foods can affect blood work results. And during surgery, you want to keep food and stomach acid from creeping back up into your airway while you’re under anesthesia. This also decreases your risk of postsurgery infections, nausea, and vomiting.

As we mentioned earlier, water fasting can help you lose weight, but it may not the best choice because it’s not very sustainable. Drastically restricting your food intake may lead to rebound weight gain by altering your hunger hormones.

It’s a better idea to make slow, gradual lifestyle changes that you can stick with in the long term.

If you’re otherwise healthy, there are safer and less extreme ways to lose weight that are more sustainable, meaning they increase your odds of keeping the weight off longer. A safe and sustainable rate of weight loss is 1 to 2 pounds per week.

If you still really want to try fasting to shed a few pounds, intermittent fasting may be a better option. The low carb keto diet can also be an effective weight loss option.

But be sure to check in with your healthcare provider before making any big changes to your diet, especially if you have any health conditions that could be affected.

Although it may have benefits, water fasting is not without risks.

Dehydration and electrolyte imbalances

Not drinking enough water or supplementing electrolytes during a water fast can result in some complications, like headaches, muscle cramps, dry mouth, fatigue, and dizziness.

Aim to drink enough water while fasting to quench your thirst and keep your urine light yellow (like a nice chardonnay). It’s also a good idea to supplement with electrolytes like sodium, potassium, and magnesium.

Nutrient deficiencies

Although one water fast may not cause any serious nutrient deficiencies, if you’re doing multiple rounds of water fasting, you could find yourself lacking in vitamins, minerals, or protein.

To prevent this, space out your fasts and consult a healthcare professional like a dietitian about any supplements you may need.

Excessive weight loss

Water fasts may result in excessive weight loss. According to the CDC, losing more than 1 to 2 pounds per week is not recommended.

Rapid weight loss can cause muscle loss, which actually decreases your metabolic rate (the calories you burn at rest). This makes it easier to regain weight when you return to your regular eating habits.

Orthostatic hypotension

Orthostatic hypotension is when you have sudden low blood pressure after quickly standing or sitting up. If you take blood pressure medications, you may be at an increased risk of this condition during periods of fasting.

If you take any blood pressure meds, talk to your doctor before attempting a fast. They may advise that you be closely monitored while fasting or avoid water fasting altogether.

Gout flare-ups

Fasting may increase the amount of uric acid in your blood, which may lead to a flare-up of gout — painful swelling and inflammation in your joints.

Diabetes complications

In select cases, fasting can result in dangerously low blood sugar levels, which is especially bad if you’re taking regular doses of insulin or other diabetes medications.

A 2017 study on rats also found that prolonged fasting may actually promote insulin resistance, which can worsen diabetes. But there’s no firm evidence in humans to support this just yet.

Promotion of disordered eating

People who have a history of disordered eating may find that fasting makes harmful eating patterns worse. If you feel like you may have disordered eating, you should talk to your doctor.

  • Water fasting is abstaining from all food and drink except water for anywhere from 1 to 3 days.
  • You should keep your healthcare provider in the know if you plan to water-fast, especially if you have diabetes or high blood pressure.
  • Water fasting may have health benefits like improving blood pressure and blood sugar levels, decreasing heart disease risk, and improving liver function.
  • Risks include dehydration, electrolyte and nutrient deficiencies, muscle loss, low blood pressure, and other health complications.
  • Although water fasting may sound like a good choice for weight loss, it’s not the most sustainable way to lose weight. Intermittent fasting is a more sustainable option.