Water Fasting: Benefits, Dangers, and Protocols

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In This Article

Water fasting is popular in the wellness world, but you should approach it with caution. While it may help you lose weight in the short-term, it’s not a sustainable approach to health or weight loss, and it puts you at risk for health complications. 

The History of Fasting

Fasting is nothing new. It’s been an integral part of many religious communities for centuries, and fasting diets have been popular since the early 1900s. One of the most popular liquid diets, the Master Cleanse, was created in the 1940s by Stanley Burrough, a self-taught alternative medicine practitioner.

Long before fasting became popular for health or fitness reasons, fasting was (and still is) practiced for religious or spiritual reasons. Fasting rituals such as those adopted during Ramadan—the month-long tradition in the Muslim community that entails strict fasting from sunrise to sunset—serve as periods of spiritual renewal and reflection for participants.

People and companies who promote fasting often use the religious example as an explanation as to why extended fasting is healthy and acceptable. Another common argument is that our paleolithic ancestors went for long periods of time without access to food, so we should also be able to.

However, many fans of the Paleo diet forget that times are vastly different and there’s no easy way to compare the eating habits of now to then. Today, there are many different detox diets that promise to cleanse the body of toxins, promote weight loss, and improve health.

Most detox diets aren’t grounded in science—rather, many people decide to fast or detox because of the apparent success stories from others.

There are several potential benefits to water fasting, but keep in mind that the science on water fasting in humans is limited. The potential risks may outweigh the benefits.

What Is Water Fasting?

A water fast is true to its name: It's a fast during which all food and drink except water are restricted. That means no coffee, no tea, no alcohol, no zero-calorie sports drinks, or any other beverage. This also means no food.

Water fasts typically last 24 to 72 hours. Medically supervised water fasts may last up to 40 days. For your safety, you should not try to fast for longer than 3 days without medical clearance and supervision.

Many popular cleanses are modeled after water fasting, such as the lemon detox cleanse, during which you drink a water-based concoction for up to 40 days. Most people embark on a water fast or similar regimen for its purported health benefits.

Water Fast Safety

Because it is not a practice that is widely endorsed by the mainstream medical or nutritional community, there are no uniform guidelines for water fasting. Most of the available tips and practices come from first-person accounts of fasts posted online by people without medical or nutritional credentials.

If you consider doing a water-fast, check with your healthcare provider to see if there are special considerations based on your current health status or medical history.

A water fast can be detrimental to people with certain medical conditions. People who should not try a water fast include those with:

  • Chronic kidney disease: Fasting may worsen kidney function
  • Diabetes: Fasting may increase a person’s risk of diabetic ketoacidosis and hypoglycemia (low blood sugar)
  • Eating disorders: Fasting may lead to disordered eating patterns like a binge-restrict cycle
  • Heartburn or gastroesophageal reflux disorder (GERD): Your stomach may continue to make stomach acid even without food, which can worsen symptoms of heartburn and GERD

Those who are under the age of 18 should also not water fast. Women who are pregnant or breastfeeding should also avoid this practice. Additionally, if you are a smoker, managing an addiction, or regularly take a prescription or over-the-counter medication, seek the personalized advice of your healthcare provider before fasting.

Water fasting presents several risks that outweigh potential benefits, and people with certain medical conditions should not attempt to water fast.

Water Fasting in a Clinic

There are a limited number of alternative medicine clinics that offer supervised water-fasts. Many who do water-fasting in a clinic environment, begin the process with a referral from their healthcare provider.

In a clinical environment, patients are monitored regularly for signs of distress such as a foul taste in the mouth, low back pain, skin rashes, discharges from mucous membranes, headaches, irritability, nausea, or vomiting. Regular blood and urine tests are also performed.

In-patient clinics may also provide educational seminars on wellness topics. They are also more likely to guide and monitor patients through the process of refeeding.

Water Fasting at Home

Many who perform water fasts at home do so without professional support and without the safety net provided by medical supervision. Because it is a fairly straight-forward process, many follow instructions found online or in magazines.

Though water fasting is simple, that doesn’t mean it’s easy. During a fast, you can’t consume anything but water. You generally drink at least 2–3 liters of water per day (ideally water consumption would be at the higher end of that range because you will not get the water you normally get from food).

Those who practice water fasts often advise that you avoid exercise or substantial physical activity during the fast. Although the advice is anecdotal, many recommend total rest during the fast. They also suggest it should be done during times of low stress.

Lastly, some recommend preparing your body for the fast by gradually decreasing your calorie consumption for a few days leading up to your fast.

After a Water Fast

If you do engage in a water fast, try to resist the urge to eat a big meal after the fast is complete. After restricting calories for an extended period of time, consuming large amounts of food can cause digestive discomfort or nausea.

At worst (though it’s unlikely), you are at risk for refeeding syndrome, a potentially fatal condition that involves rapid metabolic changes, usually in people who are extremely malnourished.

Refeeding syndrome is often a consideration in managing the health of those with eating disorders. In clinical settings, some guidelines suggest that calories are introduced very slowly (using nutritional supplements and increasing by only 10–30 calories per day) to avoid refeeding syndrome.

To get personalized guidance for safe refeeding based on the length of your fast and your current health, you should speak to your healthcare provider.

Potential Benefits of Fasting

There are possible benefits of water fasting, but it’s important to note that there is no substantial research on this topic. In fact, most of the studies on water fasting were conducted on animals, and the ones that have been conducted in humans are limited.

Additionally, it is unclear whether or not the fasting procedure itself provides the benefit. For example, simply reducing your sugar or sodium intake for a few days may provide a benefit. And for those who drink regularly, avoiding alcohol for several days may produce benefits. A full fast is not necessary to reduce your sodium, salt, or alcohol intake.

May Promote Weight Loss

You may see some weight loss during a fast, if only for a few days. By restricting caloric intake for 24 hours or more, you will more than likely experience weight loss.

Remember though, that this weight loss is probably in the form of water weight and glycogen (stored carbohydrates), and not actual fat loss. It takes a few days for your body to begin burning stored fat because it uses available energy like glucose and glycogen first.

May Lower Blood Pressure

Drinking more water and consuming less salt are two things associated with lower blood pressure readings. A water fast will enable you to do both of these things, which could help manage blood pressure. Medically supervised water fasts have shown to be effective in lowering blood pressure in patients with borderline hypertension.

However, these patients fasted for an average of nearly 2 weeks—much longer than the recommended 72-hour maximum water fast. It’s unlikely that a one- to three-day fast would create the same effect.

May Promote Cell Recycling

Every day, your cells are broken down and recycled. This process is called autophagy, and it’s thought that autophagy may play a role in preventing cancer, heart disease, and Alzheimer’s disease.

Research on water fasting in animals suggests that water fasts promote autophagy. There is little science on the relationship between water fasting and autophagy in humans, however, so we can’t say for sure that this is true.

May Lower Your Risk of Disease

There is limited evidence that water fasting can help with cancer and heart disease. One study enrolled 30 apparently healthy volunteers into a 24-hour water fast. At the end of the fast, the participants showed lower levels of triglycerides and cholesterol, two big risk factors for cardiovascular disease.

Some animal studies (mainly conducted in rats) show that water fasting can protect the animals from free radical damage to the heart. Additionally, research on animals suggests that water fasting can stop the growth of tumors, as well as improve how well an animal takes chemotherapy.

May Help Protect Against Diabetes

Research shows that fasting of any type may help to improve insulin sensitivity. Insulin resistance is the main factor in the development of type 2 diabetes, so it’s possible that short water fasts can improve insulin sensitivity and decrease the risk of diabetes.

There are several potential benefits to water fasting, but the science is inconclusive and does not position water fasts as healthful in humans.

Dangers of Water Fasting

While there may be some health advantages of fasting with water, there are some clear drawbacks that should be considered.

Nutrient Deficiencies

Any fasting protocol can put you at risk for nutrient deficiencies. By restricting calories, you are also restricting essential vitamins, minerals, fatty acids, amino acids, and electrolytes—all things your body needs to function properly.


Even though you drink water during a water fast, you can be at risk for dehydration. For most people, at least 20% of daily water consumption comes from the foods you eat. If you don’t increase your water intake during the fast, you will actually end up consuming much less water than usual.

Unsafe Blood Pressure Changes

If you drink too much water, you may experience hypotension. Hypotension is extremely low blood pressure—the opposite of hypertension, or high blood pressure.

Additionally, you may experience orthostatic hypotension, which involves sudden drops in blood pressure upon standing up. Orthostatic hypotension can cause dizziness and lightheadedness. Clinic directors also say that they monitor patients for orthostatic hypertension during water fasts. Orthostatic hypertension is a sudden increase in blood pressure upon standing.


Also called water intoxication, hyponatremia occurs when the water and salt lost through sweating are replaced by water only. You shouldn’t exercise during a water fast because you will lose salt through perspiration and won’t be able to replace it by eating food or drinking sports beverages.

Dizziness, Fatigue, and Trouble Focusing

Dizziness, fatigue, and brain fog are all symptoms of extreme calorie restriction. In fact, researchers have found that even in healthy young women, balance and stability control may be compromised during fasting.

When you don’t consume the number of calories your body needs, your body will struggle to perform at an optimal level. It may become difficult to focus at work or school during a water fast. Fasting can also cause mild-to-severe headaches.

Binge Eating

Fasting—and dieting or restricting calories in general—often leads to binge eating. Fasting can also lead to obsessive or intrusive thoughts about food, which may cause you to binge eat when your water fast is over.

At worst, recurrent fasting or extreme restriction of calories can lead to the development of disordered eating or an eating disorder.

A Word From Verywell

While water fasting may help you lose a few pounds, chances are those pounds are mainly water and glycogen (stored carbohydrates). It takes several days of calorie restriction for the body to begin burning body fat.

There are many different types of fasting that may be more beneficial and help you lose more weight sustainably, such as intermittent fasting or alternate-day fasting. There are also many ways to safely lose water weight.

If you do decide to try a water fast, you should be clear on the risks and stop the fast if you feel sick, overly fatigued, dizzy, or emotionally stressed about the fast.

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