You may have engaged in water fasting for religious reasons or as preparation for a medical procedure. Trying to lose weight with water fasting is less common, though, and best undertaken only with supervision of a medical professional. You'd experience rapid weight loss when you imbibe nothing but water, but this type of dietary strategy comes with some risks and may not be safe for everyone. Talk to your doctor before starting a water fast.
Basics of Water Fasting
The rules of water fasting are simple: You eat and drink nothing but water for the duration of the fast, which may last for several days. You also refrain from taking any vitamins, supplements or medications except thyroid medicine. People who can’t safely stop taking a prescription medication should not embark on a water fast, according to Dr. Michael Klaper, a clinician with the True North Health Center in Santa Rosa, Calif.
Dr. Julian Whitaker of the Whitaker Well Institute in Newport Beach, Calif., recommends undertaking a water fast only when you have time to relax and won’t be distracted by having to cook or grocery-shop. He advises drinking eight or more 8-ounce glasses of water a day and avoiding exercise, except for gentle walks. A water fast that lasts more than three days should be monitored by medical professionals in a facility.
A “pre-fast” period of one or two days in which you eat only fruits and vegetables may help ease you into the fast. Similarly, when you break a water fast, begin gradually by drinking fruit and vegetable juices or watery foods like melon before progressing to denser fruits and vegetables.
Rapid Weight Loss on a Fast
The amount of weight you lose on a water fast depends on the length of the fast and your body. You will initially lose water weight; fat burning does not kick in on a water fast until around day two or so.
Ben Kim, a chiropractor and acupuncturist in Toronto, says you can expect to lose about a pound a day on a water fast. If you have been following a diet high in processed foods, however, you may have retained a lot of water and sodium, so in the initial days of your water fast, you may lose as much as 3 pounds a day. Toward the end of the fast, your weight loss may stall to only a half-pound a day.
Other Benefits of Water Fasting
In addition to rapid weight loss, water fasting has other health benefits. A study conducted on people with borderline hypertension found that a medically supervised water fast of about two weeks normalized blood pressure and helped motivate patients to follow healthier lifestyles. The results were published in the Journal of Alternative and Complementary Medicine in 2002. An article in Cell Metabolism in 2014 pointed out the potential of periodic fasting for prevention and treatment of some of the chronic diseases associated with aging, such as diabetes, cancer, heart disease and loss of cognition.
Dr. Klaper maintains that water fasting helps you reset your taste buds so you are more likely to choose nutritious foods after the fast. In addition, Dr. Whitaker says it can repair the gut to help with digestive disorders. Lora Sandon, a registered dietitian, told Today’s Dietitian magazine that water fasting may also help ease rheumatoid arthritis symptoms, at least in the short term.
Risks of Fasting
Don’t undertake water fasting without consulting your doctor first, especially if you have a medical condition. This type of weight-loss strategy may not be safe for you, or you may require close supervision. In the first few days of a water fast, you will likely experience anxiety, irritability and some discomfort; Dr. Whitaker calls this the “withdrawal” period.
When you consume only water, your body misses out on other nutrients needed for best health. While fasting might not be harmful for a short period, especially for healthy people, Sandon warns that longer, unsupervised fasts -- or long detoxes of any type -- could result in deficiencies that actually cause health problems. Fasting may be particularly harmful for pregnant women, children, teens and some older adults.
Finally, if you return to unhealthy eating habits or overindulge after your water fast, you will gain back whatever weight you lost. Although water fasting may jump-start a healthy eating plan, it is not a long-term weight-management strategy.