Water Fasting: How It Works, Benefits, and Dangers (2024)

Water fasting is withholding all food and consuming only water for a short period. This practice has been around for thousands of years but has become more popular in recent times due to claims that it can lead to quick weight loss and reduce your risk for certain health conditions.

It’s important to note, however, that water fasting may cause several harmful side effects and isn’t appropriate for everyone.

This article will explain the practice of water fasting and detail the potential benefits and risks associated with it.

Water Fasting: How It Works, Benefits, and Dangers (1)

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What Is Water Fasting?

Water fasting is abstaining from eating food while continuing to drink water regularly. Fasts typically last anywhere from 24 hours to three days (or more) and are initiated as a means of reducing weight or improving one’s overall health.

While there are claims of benefits from water fasting, research on the practice is still lacking. Because of this, it is crucial to speak to a medical professional before starting a fast.

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How Does Water Fasting Work?

Because water fasting is still being studied, the guidelines surrounding it are still somewhat vague. In general, fasts can be broken into the following two phases: water fast and post-fast.

Water Fast (1 to 3 Days)

As the fast begins, food consumption ceases, and water is consumed regularly throughout the day. Some studies recommend drinking water whenever it is desired, while others are more specific about the amount you should drink.

For example, one research trial suggests drinking a minimum of 40 ounces of distilled water per day of the fast. Depending on the guidance from your healthcare provider, this phase can last for one to three days.

During this time, it is important to rest your body. Strenuous forms of exercise should be avoided, and fasts should be scheduled on days when rigorous occupational tasks are not required. In addition, not smoking is generally recommended as it can counteract any of the purported benefits of a water fast.

Water Fast Duration

While water fasts typically last for one to three days, there are online reports of fasts lasting seven days or longer. Longer duration water fasting can be dangerous and should not be attempted without significant medical supervision.

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Post-Fast (1 to 3 Days)

Once fasting is complete, the post-fast phase begins. During this time, you can slowly reintroduce small meals into your day. Some reviews recommend beginning with the Mediterranean diet, which is rich in nutrients and low in processed foods.

In addition, a three-meal (breakfast, lunch, dinner) and two-snack pattern is typically suggested to keep food intake regular. It is also crucial to remain hydrated post-fast, with one guideline recommending more than 60 ounces (1.8 liters) of water each day.

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Potential Health Benefits of Water Fasting

The evidence on water fasting is still being researched, and any possible advantages are still considered hypothetical. That said, several studies have shown positive effects on your health. The most commonly cited benefits include that it:

May Promote Autophagy

Autophagy occurs when the body recycles and rebuilds damaged portions of its own cells. This important process helps your cells withstand stresses on the body and repel invading pathogens.

Initial studies show that the process of autophagy is accelerated in individuals who are fasting. This potential benefit was found in many areas of the body, including the heart, liver, kidney, muscles, and nerves.

May Help Lower Blood Pressure

Another supposed benefit of short-term water fasting is blood pressure reduction. A small 2022 study of 48 people experiencing overweight or obesity found clinically significant reduction in both systolic and diastolic blood pressure after a 10-day water-only fast and five days of refeeding (reintroduction of food).

This supported the results of an older but notable study on the subject found that 90% of individuals with hypertension (high blood pressure) who underwent a medically supervised water fast saw their blood pressure normalize afterward.

May Improve Insulin and Leptin Sensitivity

The effects of water fasting on insulin and leptin levels may be interesting to those with diabetes or those who have obesity.

One review on the subject found that fasting from food for three days or longer led to a 30% reduction in circulating insulin levels in the body. Animal studies on fasting have also found that it led to reduced levels of leptin, a hormone that can trigger overeating and fat storage.

However, a 2022 study found increased markers of insulin resistance (when cells can't take up glucose from the blood, causing the pancreas to make more insulin) after a 10-day water-only fast and five days of refeeding. The authors speculated this might be a temporary phenomenon as the body returned to its usual energy metabolism.

May Lower Risk of Several Chronic Diseases

Initial animal studies have suggested that fasting may reduce your risk of developing several chronic diseases. This is because the practice supposedly reduces overall levels of inflammation in the body and boosts the function of your immune system.

As a result, it is hypothesized that people who perform water-fasting may experience lower incidences of diseases like:

  • Diabetes
  • Metabolic syndrome (a cluster of conditions that together can lead to heart disease, stroke, and type 2 diabetes)
  • Cardiovascular disease
  • Hypertension
  • Rheumatoid arthritis (autoimmune inflammatory arthritis affecting the synovial fluid surrounding joints)
  • Osteoarthritis (wear-and-tear arthritis)

These claims are hypothetical and need more research to support them.

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Risks and Dangers of Water Fasting

While water fasting may sound like a beneficial and healthy practice, it is extremely important to talk to a healthcare provider before trying it. Several risks and dangers are associated with this practice. Some of the most common ones are that you:

May Lose the Wrong Type of Weight

While water fasting frequently leads to weight loss, there are still some questions about whether this is a good thing. Many clinicians feel that this weight reduction is caused, in part, by the breakdown of your body’s muscle mass (called sarcopenia).

Some recent studies are calling this claim into question, however. Several clinical trials that mimic fasting have found that the practice may actually reduce your body’s excess stores of fat while preserving your lean muscle mass. More research is needed before a conclusion can be made.

May Become Dehydrated

It may seem counterintuitive that fasting from food and drinking only water can leave you dehydrated. However, much of the water in your body comes from the food you eat. Deviating from your normal diet can dramatically reduce your internal water levels.

One review of the effects of water fasting noted that several participants needed emergency care after becoming dehydrated several days into a fast.

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May Experience Orthostatic Hypotension

If water fasting causes dehydration, it may also lead to orthostatic hypotension. In this condition, there is a sudden decrease in your blood pressure when you change positions (such as going from lying down to sitting up or from sitting to standing). Symptoms associated with orthostatic hypotension include:

  • Light-headedness
  • Dizziness
  • Fainting

May Worsen Several Conditions

Water fasting has been shown to cause increased levels of uric acid in the body (hyperuricemia). As a result, it can cause flare-ups in people with a history of gout. In addition, increased uric acid levels can place additional stress on your kidneys. Because of this, water fasting is contraindicated in people with renal (kidney) diseases.

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Who Should Avoid Water Fasting?

Because of the potential dangers associated with water fasting, it is important to speak to a healthcare provider before attempting it. In addition, this practice should be avoided by people with the following medical conditions:

  • Kidney disease
  • Gout (inflammatory arthritis usually affecting the big toe)
  • Eating disorders
  • Electrolyte imbalances
  • Orthostatic hypotension
  • Pregnancy
  • Breastfeeding/chestfeeding

Will Water Fasting Help You Lose Weight?

Most people who try a water fast do so because it can cause quick reductions in body weight. One study of 12 middle-aged men found that a medically supervised eight-day water fast led to a mean weight loss of 13 pounds (5.96 kilograms).

What’s important to keep in mind, however, is that this reduction may be primarily from a loss in water weight. A small amount may also be attributed to the breakdown of your body’s muscle mass.

In addition, water fasting can lead to several adverse and potentially dangerous side effects. As a result, eating a balanced diet and regularly exercising may be a healthier way to lose weight.

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Summary

Water fasting can cause quick weight loss, but it is not without its dangers. While the practice may affect insulin sensitivity and blood pressure in positive ways, it can also lead to dehydration and orthostatic hypotension. Consult a healthcare provider before beginning any type of fast.

Water Fasting: How It Works, Benefits, and Dangers (2024)

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