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 why 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 (1Trusted Source, 2Trusted Source, 3Trusted Source). Water fasting may also promote autophagy, a process in which your body breaks down and recycles old, potentially dangerous parts of your cells (4Trusted Source). Popular diets like the lemon detox cleanseare modeled after the water fast. The lemon detox cleanse only lets you drink a mixture of lemon juice, water, maple syrup, and cayenne pepper several times per day for up to 7 days (5Trusted Source). However, water fasting has many risks and can be very dangerous if followed for too long.