Top reasons to do a longer 3 to 7 day water fast
Water fast (24–72 hours)
During a water fast, you are not allowed to eat or drink anything besides water.
Most people drink two to three liters of water per day during a water fast.
The water fast lasts for 24–72 hours. You should not water fast for longer than this without medical supervision because of health risks.
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 re feeding syndrome , 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.
A water fast usually lasts 24–72 hours and is followed by a post-fast phase. If you’re new to water fasting, you might want to spend 3–4 days preparing your body to be without food by reducing your portion sizes or fasting for part of the day.
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 ( For example, autophagy may prevent damaged parts of your cells from accumulating, which is a risk factor for many cancers. This may help prevent cancer cells from growing ( Animal studies have consistently found that water fasting helps promote autophagy. Animal studies also show that autophagy may help extend life span ( That said, there are very few human studies on water fasting, autophagy, and disease prevention. More research is needed before recommending it to promote autophagy.
May help lower blood pressure
Research shows that longer, medically supervised water fasts may help people with high blood pressure lower their blood pressure In one study, 68 people who had borderline high blood pressure water fasted for nearly 14 days under medical supervision.
At the end of the fast, 82% of people saw their blood pressure fall to healthy levels (120/80 mmHg or less). Additionally, the average drop in blood pressure was 20 mmHg for systolic (the upper value) and 7 mmHg for diastolic (the lower value), which is significant ( In another study, 174 people with high blood pressure water fasted for an average of 10–11 days.
At the end of the fast, 90% of people achieved a blood pressure lower than 140/90 mmHg the limits used to diagnose high blood pressure. Additionally, the average fall in systolic blood pressure (the upper value) was a substantial 37 mmHG ( Unfortunately, no human studies have investigated the link between short-term water fasts (24–72 hours) and blood pressure.
May improve insulin and leptin sensitivity
Insulin and leptin 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 ( For example, being more insulin sensitive means your body is more efficient at reducing its blood sugar levels. Meanwhile, being more leptin sensitive could help your body process hunger signals more efficiently, and in turn, lower your risk of obesity (
May lower the risk of several chronic diseases
There is some evidence that water fasting may lower the risk of chronic diseases like diabetes, cancer, and heart disease ( In one study, 30 healthy adults followed a water fast for 24 hours. After the fast, they had significantly lower blood levels of cholesterol and triglycerides two risk factors for heart disease ( Several animal studies have also found that water fasting may protect the heart against damage from free radicals ( Free radicals are unstable molecules that can damage parts of cells. They are known to play a role in many chronic diseases ( Moreover, animal research has found that water fasting may suppress genes that help cancer cells grow. It may also improve the effects of chemotherapy ( Keep in mind, only a handful of studies have analyzed the effects of water fasting in humans. More research in humans is needed before making recommendations.
Research shows that water fasting may lower the risk of many chronic diseases and promote autophagy. However, most research is from animal or short-term studies. More studies are needed before recommending it.
Although water fasting may have some benefits, it comes with health risks.
Here are a few dangers and risks of water fasting.