Fasting is the process of not eating food for a specific period of time. People fast for a variety of reasons. Some religions encourage their members to fast in certain circumstances. Some health professionals believe that a short-term fast can help clear the body of toxins that build up during the processes of digestion. Others use modified fasts as a way of identifying whether a person has sensitivities to certain foods.
Best bets: Short-term fasts lasting one day or less; modified fasts such as a juice fast
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During a fast, a person purposely abstains from food for a specific period of time. Fasting has been practiced throughout the ages for both religious and therapeutic purposes. A one-day fast is unlikely to cause any harm to a healthy body. Slightly longer fasts (two to three days) are also well-tolerated by most healthy people.
No matter how short the duration, fasting is unwise and potentially dangerous for some people, including pregnant and lactating women, people with cancer, diabetes, gout, hypoglycemia, stomach ulcers, liver, kidney, or lung disease, or anyone with a compromised immune system. Some health experts caution against fasts lasting more than two to three days, even for healthy individuals—if longer fasts are practiced, they should be medically supervised.
During the first 24 hours of a fast, the body is able to utilize its stored carbohydrates—in the form of glycogen—to fuel essential body processes. When glycogen reserves are depleted, fat becomes the preferred energy source, so that protein (e.g., as found in muscle tissue) is partially spared.
However, some muscle tissue is lost, even during short fasts. Weakness, nausea, headaches, and depression can also develop during a fast, because ammonia and nitrogen are released into the blood during the breakdown of muscle tissue. Ketones, byproducts of fat metabolism, are produced once the body switches from burning carbohydrates to burning fat. Elimination of ketones is accomplished by the kidneys, which makes more work for them, so people with kidney problems should be very careful, and should only fast under the supervision of a doctor. In extreme cases, extended fasts can lead to disturbances of heart rhythm and death.
“Modified” fasts, in which fruit or vegetable juices and herbal teas are consumed, are probably easier on the body than all-water fasts. Even so, a modified fast should be limited in duration; modified fasts lasting more than a week should be supervised by a healthcare professional.
Proponents claim that environmental toxins build up in our bodies over time and need to be removed periodically through fasting to maintain optimum health. Cleansing fasts are an important part of a detoxification program and may be part of a weight-loss program.
Many religions advocate fasting in various ways. Some require believers to fast altogether during certain times of year; others restrict certain food groups at specific times as in modified fasts.
Advocates believe that fasting periodically gives the body a break from digestion and allows it to eliminate the toxins that cause disease, while promoting healing and reversing the aging process. Studies indicate that fasting helps health conditions such as rheumatoid arthritis, migraine headache, and skin diseases. Acute illnesses such as colds and flu, colon disorders, allergies, obesity, and respiratory diseases may also respond to fasting. Proponents claim a one-day fast creates a clearer mental state and increased energy. They believe a three-day fast rids the body of toxins and purifies the blood, and that a long-term fast promotes healing, alleviates food allergies, sheds pounds, and rebuilds the immune system.
Critics believe that fasting depletes the body of important nutrients, essential minerals and energy, may be unsafe, and is an ineffective weight loss aid. The few pounds that are lost in the beginning of a fast are from water, and this weight will return as soon as the fast is over. Few scientific studies have been done to back up health claims and demonstrate that fasting works by releasing toxins stored in fat.
International Association of Professional Hygienists
4620 Euclid Boulevard
Youngstown, OH 44512
(A professional organization of doctors who specialize in therapeutic fasting. Write to them for a list of certified members.)
Fasting and Eating for Health: A Medical Doctor’s Program for Conquering Disease, by Joel Fuhrman, MD, New York: St. Martin’s Griffin, 1998.
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The information presented in the Food Guide is for informational purposes only and was created by a team of US–registered dietitians and food experts. Consult your doctor, practitioner, and/or chemist for any health problem and before using any supplements, making dietary changes, or before making any changes in prescribed medications.