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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
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.
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The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2016.