Water fasting entails drinking only water. Juice fasting is more permissive, incorporating fruits and vegetables in juiced form. Water fasts offer no nutrition, while juice fasting offers some calories, vitamins, minerals and antioxidants. Both kinds of fasts should be conducted for short periods of time, if at all.
Dr. Elson Haas, M.D., author of "The Detox Diet," says fasting has been used for centuries to heal a number of illnesses and works to remove toxins from the body. For general health, Harvard Medical School's Family Health Guide says the body is capable on its own of warding off environmental burdens and toxic elements. The guide suggests that instead of pursuing fasts or other detox regimens, healthy individuals eat nutritious food, get adequate water intake, exercise, sleep and get regular medical checkups to stay healthy.
Leon Chaitow, a naturopathic doctor, suggests going no more than 48 hours on a water fast. He notes that people with health conditions, lowered immunity or eating disorders should not fast, nor should people taking prescription medications unless under expert supervision. Chaitow recommends drinking at least a liter -- just over 4 cups -- and no more than 3 liters -- about 12 cups -- of water each day during the fast.
A study from the August 2005 issue of "Journal of Complementary and Alternative Medicine" found a seven-day juice fast in a medical setting improved the health of patients with several chronic illnesses. The fast consisted of less than 350 calories of juice per day. But fasts and severely low-calorie diets lack protein, fatty acids and other vital nutrients, and they can also lead to weight gain once the fast is over, as the body struggles to re-establish its normal metabolic rate.
Chaitow recommends pursuing a fast over the weekend or other "down time." This applies particularly to a water fast, which will only last a couple of days; a seven-day juice fast like the one mentioned in the "Journal of Complementary and Alternative Medicine" is also ideally done, if at all, during times when you can rest. In many cases, however, pursuing healthy habits like those suggested in Harvard's Family Health Guide are effective in maintaining health, with no hunger necessary.