What Is Water Fasting?

water cleanse

Verywell / Debbie Burkhoff 


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

Water fasting is solely consuming water, without any food at all, for the duration of the diet. It can be done for wellness reasons, or for religious and spiritual reasons. Water fasting 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. 

There are many different 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 You Can Eat

You can only drink water for the duration of the fast. Some studies that have been performed have participants drink mineral water so that at least some essential minerals could be absorbed during the fasting period.

What You Cannot 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.

How to Prepare a Water Fast & Tips

Water fasts typically last 24 to 72 hours, but medically supervised water fasts may last longer. For your safety, you should not try to fast without medical clearance and supervision.

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.

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

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 straightforward 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 to 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. Never try a water fast if you have any of these conditions.

  • Chronic kidney disease: Fasting may worsen kidney function.
  • Diabetes: Fasting may increase the 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.

People who are pregnant or breastfeeding and children and teens 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 of Water Fasting

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.

  • Reduces alcohol, sugar, and sodium intake: 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 lead to a reduction in blood pressure even with no other diet changes.
  • Lowers 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.
  • Promotes cell recycling: Every day, your cells are broken down and recycled. This process is called autophagy, and it’s thought that it 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.
  • Lowers 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.
  • Helps 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.

Cons of Water Fasting

While there may be some health advantages of fasting with water, there are also significant risks and drawbacks.

  • Digestive upset: After restricting calories for an extended period, consuming food again (especially in larger amounts) can cause digestive discomfort and nausea.
  • Risk of refeeding syndrome: 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 those living with eating disorders. In clinical settings, some guidelines suggest that calories be reintroduced very slowly (using nutritional supplements and increasing by only 10 to 30 calories per day) to avoid refeeding syndrome.
  • May cause nutrient deficiencies: Any fasting protocol can put you at risk for nutrient deficiencies. By restricting calories, you also limit your intake of essential vitamins, minerals, fatty acids, amino acids, and electrolytes—all things your body needs to function correctly.
  • May cause dehydration: 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 consume 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.
  • Hyponatremia: 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 lose salt through perspiration and won’t replace it by eating food or drinking sports beverages.
  • Unable to be physically active: In addition to the dangers of hyponatremia, it is difficult to be physically active, a vital aspect of health, because this diet contributes to lack of energy. Some studies have demonstrated that fasting causes decreased performance across a range of different fitness activities.
  • Dizziness, fatigue, and trouble focusing: Dizziness, fatigue, and brain fog are all symptoms of extreme calorie restriction. 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.
  • May lead to 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.

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, so it does not adhere to USDA guidelines and is therefore not considered a healthy way to lose weight. As a short-term diet, 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 may notice a temporary reduction in weight that lasts for a few days, which is the result of water weight and glycogen, not necessarily actual fat loss or a lasting change in your body mass.

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.

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 many health 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.

17 Sources
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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By Amanda Capritto, ACE-CPT, INHC
Amanda Capritto, ACE-CPT, INHC, is an advocate for simple health and wellness. She writes about nutrition, exercise and overall well-being.