What Is Water Fasting?

water cleanse

Verywell / Debbie Burkhoff 


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At Verywell, we believe there is no one-size-fits-all approach to a healthy lifestyle. Successful eating plans need to be individualized and take the whole person into consideration. Prior to starting a new diet plan, consult with your healthcare provider or a registered dietitian, especially if you have an underlying health condition.

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

Fasting is not a new concept. For centuries, it's been an integral part of spirituality among many religious communities. Fasting rituals such as those practiced during Ramadan—the month-long Muslim tradition that calls for strict fasting from sunrise to sunset—serve as periods of spiritual renewal and reflection for participants.

In the early 1900s, it was widely believed that fasting played a role in both weight management and disease prevention. One of the most popular liquid diets, the Master Cleanse, was developed in the 1940s by Stanley Burroughs, a self-taught alternative medicine practitioner.

Today, fasting for health or fitness reasons is fairly commonplace. Proponents of fasting often cite spiritual examples as an explanation for why fasting is healthy and acceptable. Some will argue that our paleolithic ancestors went for long periods of time without any access to food, which means we should also be able to as well. Intermittent fasting is popular among those who follow the Paleo diet—of course, the diet itself is a modern interpretation of how our ancestors once ate and not indicative of that ancient reality.

There are many different types of fasts and "detox diets" that promise to cleanse the body of toxins, promote weight loss, and improve health. But there is little scientific evidence to prove these diets—including water fasting—actually detoxify the body and support weight management.

There are some limited potential benefits to medically supervised water fasting diets, but most experts agree that the potential risks, particularly when attempted at home, far outweigh the benefits, and people with certain medical conditions should not attempt to water fast.

What Can You Eat?

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 24–72 hours, but medically supervised water fasts may last up to 40 days. For your safety, you should not try to fast without medical clearance and supervision.

Many popular cleanses are modeled after water fasting, such as the Master Cleanse, during which you drink a spicy lemonade concoction for 10–40 days. Most people embark on a water fast or similar regimen for the purported health benefits, which are mostly anecdotal.

What to Eat
  • Water

What Not to Eat
  • All other foods and liquids

What You Need to Know

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 shared by advocates without any medical or nutritional credentials.

There are a limited number of alternative medicine clinics that offer supervised water fasts. Many who undergo 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, lower back pain, skin rashes, discharges from mucous membranes, headaches, irritability, nausea, or vomiting. Regular blood and urine tests are also performed.

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, people may follow instructions found online or in magazines.

Though water fasting is simple, that doesn’t mean it’s easy or safe. 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).

Water fasting is harmful but can be especially 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.

Women who are pregnant or breastfeeding and people who are under the age of 18 should also not water fast. 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.

Pros and Cons

  • May promote quick weight loss

  • Weight loss is likely to be temporary

  • Limited health benefits

  • Numerous health risks

  • Doesn't create healthy habits

There are possible benefits of water fasting, but it’s important to note that research on the safety of a water fast is lacking, with substantial evidence pointing instead toward the potential risks.

Additionally, it is unclear whether or not the fasting procedure itself can lead to positive outcomes. 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 or more may eventually lead to weight loss and a reduction in blood pressure even with no other diet changes.

To achieve many, if not all, of the purported health benefits of a water fast, there are often safer, healthier approaches. For example, you might try reducing your sodium or alcohol intake as part of a healthy diet instead.

Is Water Fasting a Healthy Choice for You?

The 2020-2025 USDA Dietary Guidelines offer recommendations and tips for a balanced diet, which should include a variety of vegetables, fruits, grains, lean meats, beans, legumes, nuts, seeds, dairy, and healthy oils.

The water fast excludes all of these healthy food groups with the exception of water, so it does not adhere to USDA guidelines and is therefore not considered a healthy way to lose weight. As a short-term diet, however, you may see some weight loss during a water fast, but only for a few days. When you restrict your caloric intake for 24 hours or more, you will likely experience temporary weight loss.

Keep in mind 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.

A healthy diet and regular exercise are integral to successful long-term weight loss. Use the following tool to calculate how many calories you should consume each day to reach your weight loss goals.

Due to the restrictive nature of water fasting, this diet does not adhere to USDA guidelines and is not considered a healthy way to lose weight. Rapid weight loss in the form of water weight is not sustainable for long-term weight management.

Health Benefits

Despite the risks associated with water fasting, there is some research that suggests there may be a few possible health benefits. When done in the short term, water fasting may have the potential to affect the following.

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 two 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.

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.

Unfortunately, the research on the relationship between water fasting and autophagy in humans is far too limited to know for sure.

Lower Your Risk of Heart Disease

There is limited evidence that water fasting can help with 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.

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.

Health Risks

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

Digestive Upset

After restricting calories for an extended period of time, consuming large amounts of food can cause digestive discomfort and nausea.

Though unlikely, people who reintroduce calories too quickly after extended fasting are at higher risk for refeeding syndrome, a potentially fatal condition that involves rapid metabolic changes, usually in people who are extremely malnourished.

Refeeding syndrome is most often a consideration in managing the health of those living 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.

Nutrient Deficiencies

Any fasting protocol can put you at risk for nutrient deficiencies. By restricting calories, you are also restricting your intake of 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.

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 temporarily lead to weight loss, 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. More importantly, the practice doesn't come without risks.

Remember, following a long-term or short-term diet may not be necessary for you and many diets out there simply don’t work, especially long-term. While we do not endorse fad diet trends or unsustainable weight loss methods, we present the facts so you can make an informed decision that works best for your nutritional needs, genetic blueprint, budget, and goals.

If your goal is weight loss, remember that losing weight isn’t necessarily the same as being your healthiest self, and there are many other ways to pursue health. Exercise, sleep, and other lifestyle factors also play a major role in your overall health. The best diet is always the one that is balanced and fits your lifestyle.

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Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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