Other common name(s): none

Scientific/medical name(s): none

Description

Fasting involves eating no food and drinking only water or juice for a period of one to five days or longer. Tea or broth may sometimes be part of the fasting process. Fasting is often promoted as part of a "detoxification" process in some types of metabolic therapies for cancer or other conditions.

Overview

Available scientific evidence does not support claims that fasting is effective for preventing or treating cancer. Even a short-term fast can have negative health effects, while fasting for a longer time could cause serious health problems.

How is it promoted for use?

Practitioners of a type of alternative therapy called metabolic therapy (see Metabolic Therapy) believe the body contains environmental toxins and other harmful substances that can be removed by fasting or detoxifying the body. They claim that fasting allows the body to focus energy on cleansing and healing itself. According to these practitioners, fasting helps the immune system work more efficiently, allows more oxygen and white blood cells to flow through the body, helps the body to burn more fat, helps increase energy, and allows other healing functions to improve. Some supporters claim that fasting by a person who has cancer can "starve" a tumor, leading to cell death.

Other illnesses and conditions proponents claim can be treated by fasting include acne, allergies, arthritis, asthma, non-cancerous tumors, digestive disorders, fever, glaucoma, headaches, heart disease, high blood pressure, inflammatory diseases, pain, polyps, and ulcers. Fasting is also promoted to rejuvenate the body, help maintain normal body weight, increase longevity and sex drive, and to improve mental clarity, self-awareness, and self-esteem. It is also said to be helpful in quitting or cutting back on use of tobacco, alcohol, caffeine, or non-prescription drugs. Some practitioners claim it can heighten spiritual awareness.

What does it involve?

Short fasts, lasting from 1 to 5 days, are often done at home. Other than drinking only water or juice, fasting involves a lot of rest. Sometimes other methods of detoxification, such as liver flushes or enemas, are recommended as part of the regimen (see also Juicing, Liver Flush, Colon Therapy). Longer fasts require professional supervision and often take place at a spa, resort, or similar facility.

What is the history behind it?

Ancient cultures believed fasting could purify the soul. The belief that fasting can also purify or cleanse the body is a fairly modern idea, gaining popularity in the second half of the 20th century.

What is the evidence?

Available scientific evidence does not support fasting as a treatment for cancer. Some studies in animals have suggested that long-term calorie restriction -- that is, consuming less than one's normal amount of calories each day -- may slow the growth of certain tumors, but this is not the same as fasting. In fact, some animal studies have found that actual fasting in which no food is eaten several days could actually promote the growth of some tumors. No human studies on the effects of fasting on cancer have been published in the available medical literature.

A brief fast (usually 8 to 12 hours) is often advised by medical professionals in preparation for certain diagnostic tests. In this case, the fast helps to produce more accurate test results. Fasting may also be advised for a period of time before and after surgery, especially if digestive system organs are involved. This is mainly to ensure the stomach and bowels are empty during surgery. This is important in order to avoid getting stomach contents into the lungs, since anesthesia disables the usual protections, such as swallowing and coughing, that keep a person from inhaling foreign matter into the lungs when he or she is awake. It also allows the intestines time to recover from anesthesia before reintroducing food.

As for reaching and maintaining proper weight, most experts recommend a combination of limiting portion sizes, choosing healthful foods, and being physically active instead of fasting.

Some research has suggested that short-term fasts may briefly improve the symptoms of rheumatoid arthritis. However, the benefits do not last longer than 10 days, and fasting is not a recommended component of arthritis care.

Are there any possible problems or complications?

Fasting can have short-term side effects such as headaches, dizziness, fatigue, abnormal heart rhythms, and a fruity taste in the mouth. It can also raise the risk of an attack in people with gout. Longer-term fasting can interfere with the immune system and vital bodily functions and can damage the liver, kidneys, and other organs. Fasting can be especially dangerous in people who are already malnourished, such as those with some forms of advanced cancer. Women who are pregnant or breast-feeding should not fast.

Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Additional Resources

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).

• Guidelines for Using Complementary and Alternative Methods

• How to Know What Is Safe: Choosing and Using Dietary Supplements

• The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

• Complementary and Alternative Methods for Cancer Management

• Placebo Effect

• Learning About New Ways to Treat Cancer

• Learning About New Ways to Prevent Cancer

References

Caderni G, Perrelli MG, Cecchini F, Tessitore L. Enhanced growth of colorectal aberrant crypt foci in fasted/refed rats involves changes in TGFbeta1 and p21CIP expressions. Carcinogenesis. 2002;23:323-327.

Cassileth B. The Alternative Medicine Handbook. New York: W. W. Norton & Co; 1998.

Hikita H, Nuwaysir EF, Vaughan J, et al. The effect of short-term fasting, phenobarbital and refeeding on apoptotic loss, cell replication and gene expression in rat liver during the promotion stage. Carcinogenesis. 1998;19:1417-1425.

Hikita H, Vaughan J, Pitot HC. The effect of two periods of short-term fasting during the promotion stage of hepatocarcinogenesis in rats: the role of apoptosis and cell proliferation. Carcinogenesis. 1997;18:159-166.

Legro RS, Finegood D, Dunaif A. A fasting glucose to insulin ratio is a useful measure of insulin sensitivity in women with polycystic ovary syndrome. J Clin Endocrinol Metab. 1998;83:2694-2698.

PDRhealth. Detoxification therapy. 2004. Accessed at: www.pdrhealth.com/content/natural_medicine/chapters/201160.shtml on August 4, 2005. Content no longer available.

PDRhealth. Fasting. 2004. Accessed at: www.pdrhealth.com/content/natural_medicine/chapters/201200.shtml on August 4, 2005. Content no longer available.

Sesca E, Premoselli F, Binasco V, Bollito E, Tessitore L. Fasting-refeeding stimulates the development of mammary tumors induced by 7,12-dimethylbenz[a]anthracene. Nutr Cancer. 1998;30:L25-30.

Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

Last Medical Review: 11/01/2008
Last Revised: 11/01/2008