Water fasting may offer several health benefits, including weight loss and a reduced risk of some chronic conditions. However, it is also associated with several risks and may not be suitable for everyone.
Fasting, a method of restricting food intake, has been practiced for thousands of years.
Water fasting is a type of fast that restricts everything except water. It has become more popular in recent years as a quick way to lose weight.
For example, it may lower the risk of some chronic diseases. Trusted Source and stimulate autophagy, a process that helps your body break down and recycle old parts of your cells.
That said, human studies on water fasting are very limited. Moreover, it comes with many health risks and is not suitable for everyone.
This article gives you an overview of water fasting and how it works, as well as its benefits and dangers.
What is water fasting?
Water fasting is a type of fast during which you cannot consume anything besides water.
Most water fasts last 24–72 hours. You should not follow a water fast for longer than this without medical supervision.
Here are a few reasons why people try water fasting:
religious or spiritual reasons
to lose weight
for "detoxing"
for its health benefits
preparing for a medical procedure
The main reason people try water fasting is to improve their health.
In fact, several studies have linked water fasting with some impressive health benefits, including a lower risk of certain cancers, heart disease, and diabetes.
Water fasting may also promote autophagy, a process in which your body breaks down and recycles old, potentially dangerous parts of your cells.
Popular diets like the lemon detox cleanse are modeled after the water fast. The lemon detox cleanse from Trusted Source only lets you drink a mixture of lemon juice, water, maple syrup, and cayenne pepper several times per day for up to 7 days.
However, water fasting has many risks and can be very dangerous if followed for too long.
Water fasting is a type of fast during which you’re not allowed to consume anything except water. It’s linked with a lower risk of chronic disease and autophagy, but it also comes with many risks.
How do you fast?
There are no scientific guidelines on how to start water fasting.
However, several groups of people should not fast without medical supervision.
This includes people with gout, diabetes (both types 1 and 2), eating disorders, older adults, people who are pregnant, and children. Trusted Source.
If you have never fasted before, it’s a good idea to spend 3–4 days preparing your body for being without food.
You can do this by eating smaller portions at each meal, or by fasting for part of the day.
Water fast (24–72 hours)
During water fast, you are not allowed to eat or drink anything besides water.
Most people drink two to three liters of trusted source water per day during a water fast.
The water fast lasts for 24–72 hours. You should not fast for longer than this without medical supervision because of health risks.
Some people may feel weak or dizzy during water fast and may want to avoid operating heavy machinery and driving to avoid causing an accident.
Post-fast (1–3 days)
After the water fast, you should resist the urge to eat a big meal.
This is because eating a large meal after a fast may cause uncomfortable symptoms.
Instead, break your fast with a smoothie or smaller meals. You can start introducing larger meals throughout the day as you feel more comfortable.
The post-fast phase is especially important after longer fasts. This is because you may be at risk of reseeding syndrome. Trusted Source, a potentially fatal condition in which the body undergoes rapid changes in fluid and electrolyte levels.
This phase normally lasts a day, but people who fast for 3 or more days may need up to 3 days before they feel comfortable eating larger meals.
Potential benefits of water fasting
Both human and animal studies have linked water fasting to a variety of health benefits.
Here are a few health benefits of water fasting:
May promote autophagy
Autophagy is a process in which old parts of your cells are broken down and recycled.
Several animal studies suggest that autophagy may help protect against diseases like cancer, Alzheimer's, and heart disease.
May help lower blood pressure.
Research shows that longer, medically supervised water fasts may help people with high blood pressure lower their blood pressure.
One study in 48 people with overweight or obesity found that water fasting for an average of 17 days under medical supervision led to reductions in systolic blood pressure.
It was also associated with improvements in levels of LDL (bad) cholesterol and inflammation.
Similarly, another review by Trusted Source concluded that water fasting could significantly reduce blood pressure levels and body weight in people with high blood pressure.
Still, more research is needed to evaluate the link between short-term water fasts (24–72 hours) and blood pressure.
May improve insulin and leptin sensitivity.
Insulin (trusted source) and leptin (trusted source) are important hormones that affect the body’s metabolism. Insulin helps the body store nutrients from the bloodstream, while leptin helps the body feel full.
Research shows that water fasting could make your body more sensitive to leptin and insulin. Greater sensitivity makes these hormones more effective.
Being more insulin-sensitive means your body is more efficient at reducing its blood sugar levels. Meanwhile, being more leptin-sensitive A trusted source could help your body process hunger signals more efficiently, lowering the risk of obesity.
May lower the risk of several chronic diseases.
There is some evidence that water fasting may lower the risk factors for chronic diseases like diabetes, cancer, and heart disease.
Free radicals are unstable molecules that can damage parts of cells. They are known to play a role in many chronic diseases.
Moreover, studies in animals and humans have found that water fasting may suppress genes that help cancer cells grow. It may also improve the effects of chemotherapy.
Keep in mind that only a handful of studies have analyzed the effects of water fasting on humans. More research on humans is needed before making recommendations.
Dangers and risks of water fasting
Although water fasting may have some benefits, it comes with health risks.
Here are a few dangers and risks of water fasting:
May lose the wrong type of weight.
Because water fast restricts calories, you will likely lose a lot of weight quickly.
May become dehydrated.
Although it sounds strange, water fast could make you dehydrated. This is because roughly 20–30% of your daily water intake comes from the foods you eat.
If you’re drinking the same amount of water but not eating food, you might not be getting enough water.
Symptoms of dehydration include dizziness, nausea, headaches, constipation, low blood pressure, and low productivity. To avoid dehydration, you may need to drink more than usual.
May experience or tho static hypotension.
Dehydration caused by water fasting can lead to or tho static hypotension. Trusted Source.
Or tho static hypotension Trusted Source is defined as a drop in blood pressure that happens when you suddenly stand up, and it can leave you dizzy, lightheaded, and at risk of fainting.
If you experience orthostatic hypotension while fasting, you may need to avoid driving or operating heavy machinery. The dizziness and risk of fainting could lead to an accident.
If you experience these symptoms during water fast, this type of fasting may not be a good option for you.
Fasting may worse several medical conditions.
Although water fast is relatively short, there are a few conditions that may be aggravated by it.
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