Spiritual and Religious Fasting
Whether fasting can help rid the body of waste buildup is a matter of controversy. But fasting has been used for religious and spiritual purification for centuries.
Nearly every religious text you can name, from the Old and New Testaments of the Bible to the Quran and the Upanishads, calls upon followers to fast periodically as a rite of spiritual purification, penitence, or preparation for union with God.
Medical Reasons for Fasting
Another topic on which there is medical agreement is the benefit - actually, the necessity -- of fasting before surgery.
"You don't want the body to be digesting food as it manages the slower breathing [and other body changes] under anesthesia," says Fernstrom.
Fasting is also required to get accurate readings for certain medical tests. Short-term fasting before tests for cholesterol and blood sugar levels, for example, helps achieve a more accurate baseline count.
Fasting to Treat Disease
Fasting advocates also claim that the practice can effectively treat serious health conditions, from arthritis and colitis to heart disease and depression.
In his practice, Fuhrman tells WebMD, he has seen fasting -- combined with improving the diet before and afterward -- eliminate lupus, arthritis and chronic skin conditions like psoriasis and eczema. He says he has also seen fasting heal the digestive tracts of those with ulcerative colitis and Crohn's disease, and lower blood pressure.
"Fasting followed by a vegetarian diet interferes with the immune system's activities, especially if the immune system is overreacting, as it does with ," and other auto-immune diseases, he says. He cites half a dozen studies published in medical journals ranging from the American Journal of Physiology - Endocrinology and Metabolism to the Scandinavian Journal of Rheumatology.
Studies published in The Proceedings of the National Academy of Sciences and The Journal of Nutrition in 2003 showed that mice forced to fast every other day, while eating twice the normal amount of food on non-fasting days, had better insulin control, neuronal resistance to injury, and other health indicators than mice fed calorie-restricted diets.
Fasting may yield psychological benefits as well.
"I use very brief fasting with my patients to help them cope with stress and depression," says Agnese Barolo, a life coach in contemplative practices in New Rochelle, N.Y. "I start them with just a few hours â so they learn to say no to food. Itâs the first step in taking control of their lives."