What Is It?
How Does It Work?
What You Can Expect

Health Benefits

How To Choose a Practitioner



Evidence Based Rating Scale


What Is It?

Strictly defined, fasting is abstinence from all food and drink (except water) for a limited period of time to maintain or improve health, or to treat a specific illness. Juice fasting, a popular variation, is abstinence from all food and drink except water and vegetable and fruit juices. A modified fast includes small amounts of solid food, usually raw fruits as well as raw and steamed vegetables. Some advocates of fasting also include other modifications, such as vegetable broth, herbal teas, brown rice, and nutritional supplements. Most of the research examining the therapeutic value of fasting has explored the water-only method.

A short fast, which lasts from one to three days, is generally well tolerated by most people who are otherwise healthy and who are not pregnant or breastfeeding. An extended fast lasting more than three days should be supervised by a doctor, such as one trained in fasting therapy.

Fasting has been practiced since ancient times. In fact, there are references to it in the Bible, the Koran, and ancient Chinese and Greek medical texts. Historically, people have fasted as part of religious rituals, as a way of expressing grief, and as part of political protests. Fasting to benefit health is a relatively new practice and is generally undertaken only in prosperous Western societies.

One of the first doctors in the United States to advocate fasting was Isaac Jennings, M.D. (1788-1874) of Fairfield, Connecticut. Jennings rejected the therapeutic use of drugs to treat specific ailments and instead developed a treatment program that included periodic fasting, a vegetarian diet, pure water, sunshine, clean air, exercise, and rest. His program, which came to be known as the Natural Hygiene system, is still practiced today, and doctors who follow it usually specialize in overseeing therapeutic fasts.

Perhaps the best-known modern proponent and practitioner of therapeutic fasting was Herbert M. Shelton (1895-1985), a chiropractor and naturopath who developed a strict (water only) fasting protocol in the late 1920s. In 1928, Shelton founded his own health school, and in 1948 he helped to establish the American Natural Hygiene Society to further promote fasting and a holistic lifestyle to a lay public. In 1978, he formed a professional branch, today known as the International Association of Hygienic Physicians (IAHP). The organization publishes research on fasting and provides certification in fasting therapy to physicians in the fields of medicine, osteopathy, chiropractic, and naturopathy.

How Does It Work?

Critics of fasting therapy often confuse fasting with starvation. In the fasting state, nonessential tissue, such as Fat, is used for fuel while vital organs are spared. Starvation occurs when the body has depleted its fat stores and begins to use vital organs for fuel. Obviously, if the body does not receive food after a supervised fast, starvation and death will inevitably follow.

The series of physiologic events that occurs within the body during a fasting state has been well-studied and follows a definite sequence. Basically, the body undergoes certain changes in metabolism to conserve its energy sources but continues to function with the same degree of efficiency. For example, blood sugar levels remain fairly constant no matter how long the fast lasts.

Early in fasting, the body both manufactures glucose (gluconeogenesis) and releases stores of it from within the liver (glycogenolysis). After a few days, the body will release triglycerides from fat cells. These tryglycerides become oxidized and form acids called ketones, which are then used for energy production. All of these changes slow the overall metabolism of the body to about 75% of its normal rate. For this reason, plenty of rest (and no vigorous exercise) is routinely advised while fasting.

There is very little published evidence that fasting has any value for a healthy individual. Even so, practitioners of naturopathic medicine regularly recommend fasting as the therapeutic tool for internal cleansing, otherwise known as detoxification. Periodic fasting, naturopaths believe, helps overworked systems (the gastrointestinal tract, skin, liver, and kidneys) remove potentially damaging toxins from the body.

Not surprisingly, a naturopath's definition of what constitutes a "toxin" goes beyond that of conventional medicine. And while both camps tend to agree that certain heavy metals (lead, cadmium, mercury) and chemical compounds (pesticides, herbicides, solvents) are toxic, naturopaths expand the list to include food additives, many commonly prescribed drugs, cigarettes, recreational drugs and alcohol, and substances produced by bacteria-induced chemical reactions in the intestine.

In addition to using fasting for cleansing purposes, many healthy individuals find it a useful way of weaning themselves off of unhealthy foods. A fast of no more than three days can be used to launch a healthier diet--for example, eliminating coffee or changing to a vegetarian diet from a meat-based regimen.

A fast can also be an effective way to begin a low-Calorie diet, a signal to your body that you're altering the way you eat. But the hunger produced from a fast can lead some people to binge afterward. The "yo-yo" effect of fasting and binging can slow down metabolism, making it harder to lose weight in the long run.

What You Can Expect

If a primary-care practitioner isn't willing to supervise a fast, seek a naturopathic physician, nutritionally oriented chiropractor, nutritionist, or registered dietitian. Before beginning a fast, the practitioner should take a medical history, conduct a physical examination, and perform other tests to be sure that the patient’s body is up to the challenge of a fast.

Prepare for the fast with a day of eating light vegetarian meals, focusing on raw fruits plus raw and steamed vegetables. Throughout the fast, drink plenty of liquids--water, for a strict fast, and non-acidic juices and herbal teas for a modified fast. Continue any prescription medicines for specific conditions, but stop taking any nutritional supplements during the fast. The method of stopping a fast is also important. Ease back into solid food the same way the fast began--with light meals of fruits and vegetables. A large amount of food right away may be too much for the body to comfortably handle.

The beginning of a fast may feel energizing. Or, hunger may trigger headaches, dizziness, fatigue, and irritability. As time goes on, a calm and heightened sense of well-being and clarity of mind may set in. Sleep patterns may be disrupted, however. Be sure to nap during the day if sleep at night is lighter. In addition, the tongue may feel furry or coated, and bad breath may develop. Use a mouth rinse of plain water or water mixed with lemon juice to relieve these symptoms. If dizziness, nausea, aching limbs, or visual or hearing disturbances are bothersome, contact your practitioner.

Don't expect to pursue regular activities during a fast. For a weekend fast, stay close to home, and limit exercise to walks, stretching exercises, yoga, or tai chi. Good pastimes are meditating, napping, reading, and listening to relaxing music.

Health Benefits

Published research into therapeutic fasting first appeared in the late nineteenth century. Since that time, articles have appeared in conventional medical journals in both the United States and Europe showing the positive results of supervised fasting in treating various diseases, including obesity, cardiovascular disease, autoimmune disorders, diabetes, skin disease, gastrointestinal disease, arthritis, and allergies.


Specifically, fasting may help to:

Lose weight. The majority of published evidence regarding the health benefits of fasting is most often related to weight loss in obese patients. On average, initial weight loss during fasting has been found to be about 0.30% of body weight per day, gradually decreasing to 0.10% daily after 30 days of fasting. (1) Numerous articles published in the early and mid-1900s advocated short and long fasts as safe and effective means of losing weight. And in 1973, one of the most famous studies on obesity was published in the Postgraduate Medical Journal. In this case study, a 27-year-old man fasted without complications for 382 days and lost 276 pounds. (2) However, results from a 1976 long-term study of 132 fasting patients were not remarkably favorable. The patients underwent a long fast while supervised in a hospital, and researchers followed their weight loss between 1 to 6.5 years later. Of the 132 patients, 64 (48%) were considered to be successful upon follow-up: 37 patients had continued to lose weight, 20 patients had maintained their fasting result, and 7 patients had regained less than one-third of the weight lost during the fast. The group’s mean obesity dropped from 57% to 29%, which at the time corresponded to a 60% reduction of mortality in certain age groups. However, five patients were lost to follow-up and the remaining 63 of the 132 patients (48%) had regained more than one-third of their original weight loss. (3) In general, studies have found that fasting alone, without counseling or other lifestyle modifications, does not ensure long-term maintenance of the lower body weight achieved through fasting. A 1982 review of studies found rapid weight loss can be achieved by fasting, but long-term success is most often achieved through a combination of techniques, including counseling, behavior modification, exercise, proper nutritional instruction and a protein-sparing modified fast (for those 30% or more over their ideal body weight). (4)

Treat diabetes. Many patients with Type 2 diabetes are significantly overweight, and weight loss can provide marked improvement in their blood glucose levels. Researchers also are interested in the effect of fasting on blood glucose levels, in addition to potential weight loss from fasting. Some proponents of fasting believe it not only detoxifies cells and rejuvenates organs but also may cure conditions such as diabetes by restoring pre-diabetic conditions. However, evidence of this has thus far only been anecdotal. While fasting can be dangerous for patients with diabetes, especially in those requiring drugs to maintain healthy insulin levels, some studies are beginning to examine the potential of fasting to treat diabetes. A 1999 study investigated the effect of intermittent feeding and fasting on diabetes in rats. The rats were divided into three groups: Group 1 was the control group; food (but not water) was withdrawn for 24-hour intervals twice a week in Group 2; and food (but not water) was withdrawn for 24-hour intervals every second day in Group 3. During the study, 79% of the control group became diabetic, and 50% and 52% of groups 2 and 3, respectively, became diabetic. In the non-diabetic rats, blood glucose values at the end of the study had reduced on the altered food regimen. And intermittent feeding and fasting caused reduced weight gain in groups 2 and 3, compared to the control group. Researchers concluded that intermittent feeding and fasting reduced the incidence of diabetes in rats. (5) More recently, in 2003, laboratory mice on a regimen of fasting every other day while eating double the normal amount of food on non-fasting days had improved health indicators including insulin and blood sugar control and neuronal resistance to injury compared to mice eating 40 percent calorie-restricted diets on a daily basis. (6, 7) More research is needed to determine the effects of fasting on diabetes in humans.

Treat cardiovascular risk factors. In the 1960s, researchers began to study the effects of fasting on heart disease after earlier studies concentrating on weight loss had shown potential for improving symptoms such as hypertension and cholesterol levels. Preliminary studies showed improved reductions in serum triglyceride values, blood pressure, atheromas (swelling of arterial walls caused by cholesterol), and total cholesterol levels. For example, a case study published in the Lancet in 1966 showed that fasting for 249 days to treat obesity also increased the ratio of HDL cholesterol to total cholesterol; and the famous 1973 study published in the Postgraduate Medical Journal about a 382-day fast also noted similar improvements in cholesterol. (8, 2) And in a 2001 study of 174 patients with high blood pressure (HBP), researchers studied the effects of a water-only fast for treatment. The patients underwent a brief pre-fast period eating only fruits and vegetables, followed by a water-only fast for 10 to 11 days and a refeeding period of about six to seven days to introduce a low-fat, low-sodium, vegan diet. Almost 90% of subjects achieved BP lower than 140/90 mmHg by the end of the program, with an average reduction in blood pressure being 37/13 mmHg. In patients with stage III hypertension (systolic BP greater than 180 mmHg), the average reduction in systolic BP exceeded 60 points. This was the largest effect published to this date. (9) Nine months later, the same lead researcher studied 68 patients with HBP (over 119/91 mmHg). The patients underwent a pre-fast period of fruits and vegetables, followed by about 13 days of water-only fasting and then a six-day refeeding program similar to the previous study. About 82% of the subjects achieved BP at or below 120/80 mmHg by the end of the program, with an average ending BP of 99/67 mmHg. (10) And in a letter to the editor published in the Journal of Alternative and Complementary Medicine in December 2002, the same researcher described initial results in 30 patients with HBP participating in a residential health education program that included the supervision of water-only fasting for an average of 14 days. The BP, weight, and cost of treatment and medications were compared for the year prior to and the year after fasting. Results from the study showed improvements in BP and weight reduction had been maintained, as well as an average reduction in combined medical and drug costs of almost $2,700 per year per subject. (11)

Manage rheumatoid arthritis. Researchers have found a strong link between diet and rheumatoid arthritis (RA) – both in terms of cause and cure. This chronic inflammatory condition is often aggravated by allergenic foods such as wheat, dairy products, beef, and food additives. Eliminating the offending foods first through fasting and then reintroducing safe foods may help some patients with RA. Fasting helps to reduce the absorption of allergenic food components from the gastrointestinal tract and to reduce the levels of inflammatory mediators. (12) Preliminary anecdotal evidence from scientists indicated anti-inflammatory effects of fasting, noticeable through decreases in arthralgia, pain, stiffness, and need for medication. Consistent with those findings, a 1984 study of 43 patients with definite or classic rheumatoid arthritis found significant improvements in grip strength, pain, swelling of proximal interphalangeal joints (the finger joints closest to the hand), and functional activity after fasting for seven days. (13) Similarly, in a 1991 controlled study published in Lancet, 27 patients with RA were studied for 13 months to determine the effect of diet on their condition. The patients were divided into two groups: one group began with a 7- to 10-day liquid fast (vegetable juices, teas, broths; no fruit juices) and then were treated with a gluten-free vegan diet, and the control group continued to eat what they wanted. After the fast, the patients in that group reintroduced a “new” food item every second day. If they noticed an increase in pain, stiffness, or joint swelling within two to 48 hours, the item was omitted from the diet for at least seven days before being reintroduced a second time. If the food caused worsening of symptoms after the second time, it was omitted permanently from the patient’s diet. After four weeks, the fasting/diet group showed a significant improvement in several symptoms, including number of tender joints, number of swollen joints, pain score, duration of morning stiffness, grip strength, C-reactive protein, white blood cell count, and a health assessment questionnaire score. In the control group, only the pain score improved significantly. At one-year follow-up, all patients whose RA responded to the diet were still following it. Researchers noted the therapeutic benefit of fasting and a special diet on eliminating food allergies and improving dietary fatty acids, which act as inflammatory mediators. (14)

Test for food allergy. As with the rheumatoid arthritis study, fasting has been used as a diagnostic test to determine food intolerances. After a five-day water-fast, patients with suspected food allergies introduce suspected foods to determine when a reaction occurs. Proponents believe it is necessary to fast for at least 5 days to rid the body of all allergic responses. (15) Researchers have found that the primary therapy for food allergy in adults and children is to first eliminate the responsible food. (16-18)

Improve skin conditions such as eczema and psoriasis. The anti-inflammatory effects of fasting also may be useful in treating some skin conditions characterized by inflammation. Researchers believe fasting may improve symptoms of eczema and psoriasis, but few studies have examined this potential treatment. In a 1983 study of 20 patients who underwent a two-week modified fast followed by a three-week vegan diet, patients with eczema and psoriasis showed improvement of symptoms during the fast. Signs and symptoms of eczema and psoriasis returned in most patients during the diet phase, with the exception of some patients with psoriasis who experienced an improvement. (19) This preliminary evidence indicates potential efficacy, but the small sample size is limiting. More research is needed in this area to confirm or refute efficacy.

How To Choose a Practitioner

Because fasting is not included in conventional medical training, the number of physicians utilizing this therapeutic tool remains very small. While a primary-care physician may be willing to supervise a short fast, longer fasts should be guided and monitored by a naturopathic physician, nutritionally oriented chiropractor, nutritionist, or registered dietitian. Ask your primary-care practitioner for a referral.

Patients with a chronic medical problem interested in the benefits of fasting as a therapeutic modality specific to that condition should locate a nutritionally oriented physician or naturopath with some experience in the field.

A directory of practitioners who specialize in fasting therapy is available through the International Association of Hygienic Physicians (IAHP), in Youngstown, Ohio.


  • Even healthy individuals should not undertake an extended fast of more than three days without medical supervision.

  • Pregnant or breast-feeding women should not fast.

  • Patients with advanced cancer, a compromised immune system, diabetes, ulcers, or liver, kidney, heart, or lung disease, should never fast without medical supervision.

  • Fasting as part of the treatment for a chronic disease such as heart disease, epilepsy, arthritis, or schizophrenia should be under the supervision of a physician experienced in the field.

  • Anyone who takes prescription or recreational drugs regularly should not fast without medical supervision. Withdrawal symptoms can develop quickly during fasting.

  • It's important to break a fast carefully. Eating too much too soon can overload the digestive system, causing uncomfortable and disruptive reactions. A doctor can help determine how best to break a fast based on individual needs.


1. Shils ME. Modern nutrition in health and disease, 9th ed. Philadelphia: Lea & Febiger, 1998.
2. Stewart WK, Fleming LW. Features of a successful therapeutic fast of 382 days’ duration. Postgrad Med J. 1973;49:203-9.
3. Goschke H, Hausser R, Lauffenburger TH, et al. [Long-term results of fasting. Results from 132 consecutive patients after 1-6 1/2 years]. Schweiz Med Wochenschr. 1976 May 22;106(21):713-7.
4. Linet OI. Long-term efficacy of medical treatments of obesity. Klin Wochenschr. 1982 Feb 1;60(3):115-20.
5. Pedersen CR, Hagemann I, Bock T, Buschard K. Intermittent feeding and fasting reduces diabetes incidence in BB rats. Autoimmunity. 1999;30(4):243-50.
6. Anson RM, Guo Z, de Cabo R, et al. Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake. Proc Natl Acad Sci USA. 2003 May 13;100(10):6216-20.
7. Wan R, Camandola S, Mattson MP. Intermittent food deprivation improves cardiovascular and neuroendocrine responses to stress in rats. J Nutr. 2003 Jun;13(6):1921-9.
8. Thompson TJ, Runcie J, Miller V. Treatment of obesity by total fast for up to 249 days. Lancet. 1966;2:992-6.
9. Goldhamer AC, Lisle DJ, Parpia B, et al. Medically supervised water-only fasting in the treatment of hypertension. J Manipulative Physiol Ther. 2001;24:335-9.
10. Goldhamer AC, Lisle DJ, Sultana P, et al. Medically supervised water-only fasting in the treatment of borderline hypertension. J Altern Complement Med. 2002 Oct;8(5):643-50.
11. Goldhamer AC. Initial cost of care results in medically supervised water-only fasting for treating high blood pressure and diabetes. J Altern Complement Med. 2002 Dec;8(6):696-7.
12. Sundqvist T, Lindstrom F, Magnusson KE, et al. Influence of fasting on intestinal permeability and disease activity in patients with rheumatoid arthritis. Scand J Rheumatol. 1982;11:33-8.
13. Kroker GF, Stroud RM, Marshall R, et al. Fasting and rheumatoid arthritis: a multicenter study. Clin Ecol. 1984;2:137-144.
14. Kjeldsen-Kragh J, Haugen M, Borchgrevink CF, et al. Controlled trial of fasting and one-year vegetarian diet in rheumatoid arthritis. Lancet. 1991 Oct 12;338(8772):899-902.
15. Rinkel HJ, Randolph T, Zeller M. Food allergy. Springfield, IL: CC Thomas, 1951.
16. Grimshaw KE. Dietary management of food allergy in children. Proc Nutr Soc. 2006 Nov;65(4):412-7.
17. Fiocchi A, Martelli A. Dietary management of food allergy. Pediatr Ann. 2006 Oct;35(10):755-6, 758-63.
18. Burks W. Current understanding of food allergy. Ann NY Acad Sci. 2002 May;964:1-12.
19. Lithell H, Bruce A, Gustafsson IB, et al. A fasting and vegetarian diet treatment trial on chronic inflammatory disorders. Acta Derm Venereol. 1983;63(5):397-403.

Evidence Based Rating Scale 

The Evidence Based Rating Scale is a tool that helps consumers translate the findings of medical research studies with what our clinical advisors have found to be efficacious in their personal practice. This tool is meant to simplify which supplements and therapies demonstrate promise in the treatment of certain conditions. This scale does not take into account any possible interactions with any medication/ condition/ or therapy which you may be currently undertaking. It is therefore advisable to ask your doctor before starting any new treatment regimen.



Date Published: 04/19/2005

Previous  |  Next
> Printer-friendly Version

© 2000- 2019 ., LLC. 21251 Ridgetop Circle, Suite 150, Sterling, VA 20166. All rights reserved. Reproduction in whole or in part without permission is prohibited. Privacy Policy

Disclaimer: All material provided in the WholeHealthMD website is provided for educational purposes only. Consult your physician regarding the applicability of any information provided in the WholeHealthMD website to your symptoms or medical condition.