Water Fasting

Religious and naturopathic roots

A 2013 expert panel of German-speaking physicians, writing in a journal of complementary medicine, states that voluntary fasting traditions developed with ethno-cultural variations, either in religious and spiritual contexts or for medical therapeutic purposes. The panel describes a long tradition of naturopathy (Naturheilkunde) in Germany in which a health-promoting lifestyle, specific nutritional therapies and fasting are central. The panel members are drawn largely from fasting clinics, so this is an account from within the field.

A 2019 clinic study states that fasting in various forms appears in most religions and that Otto Buchinger's periodic fasting program is well known in central Europe. The sources reviewed for this page do not give a dated, independent history of fasting in antiquity, so claims about Hippocratic or other ancient medical fasting are not made here.

Buchinger and the German schools

The 2013 expert panel names two important schools of fasting in German-speaking countries: the fasting regimen (Heilfasten) developed by Otto Buchinger (1878 to 1966) and the medical fasting regimen according to Franz Xaver Mayr. It says Buchinger and his followers built a multidisciplinary inpatient concept in which fasting is combined with physiotherapy, nutrition, mind-body methods, psychotherapy and physical activity, and that parts of the religious fasting tradition, such as mindfulness and group support, remained components of it.

The same panel records that fasting has been taught in postgraduate medical education in Germany since 1978 and that a medical society for fasting and nutrition has granted a training certificate to physicians since 1996. Nonmedical fasting guide courses have been offered since 1986. The sources reviewed do not give the year Buchinger began his program, so the date is not stated here.

Russian fasting-dietary therapy

Russian clinics have used a supervised program often translated as fasting-dietary therapy, associated with the psychiatrist Yuri Nikolayev. No peer-reviewed or professional-body source on its history could be opened and verified for this page, and the only accounts found were popular press articles, which are not cited. Readers should treat the Russian tradition as outside what the verified sources cover.

Water-only and modified fasting

The 2013 expert panel defines fasting as voluntary abstinence from solid food and stimulants for a limited period. It notes that water-only fasting and several types of modified fasting differ, although all involve partial or total interruption of food intake, and that the terms are often mixed up. It also says the word fasting is sometimes used for weight-loss diets such as very low calorie diets, which it treats as a separate matter.

Buchinger-style fasting, as described by the panel and used in the large German clinic study, is a medically supervised modified fasting regimen with a small amount of liquid nutrition and not strictly water alone. Studies of strictly water-only fasting come mainly from a US residential center. Findings from one form should not be carried over to the other.

Therapeutic, preventive and religious fasting

The panel separates therapeutic fasting for a medical condition, preventive fasting, and fasting for healthy people without a medical intention. German usage of Heilfasten is often rendered in English with wording that implies an outcome, which this page does not adopt. Religious fasting, such as the daytime fasting of Ramadan in Islam, is a distinct practice with different timing and aims, and it is not the subject of the clinic studies discussed below.

Setting and supervision

In the 2019 clinic study, participants were inpatients at a single fasting clinic in Germany. Nurses and physicians supervised them daily, physicians examined them several times a week, and certified trainers led a moderate exercise program. The 2024 US trial of strictly water-only fasting took place in a residential fasting center with 24-hour medical supervision. Both papers describe supervision as part of the intervention being studied.

The 2013 expert panel says that for safety and quality all interventions during fasting should be guided by physicians or therapists trained and certified in fasting therapy, and that medical examination before and during fasting is expected. This is the position of the panel, whose members work in fasting clinics. Details of schedules and procedures are not reproduced on this page.

Fasting within a program

Clinic programs described in the sources place the fast between a preparatory period and a period of gradual return to food, and add exercise, rest, group support and education. The US hypertension trials combined a medically supervised water-only fast with a plant-based diet afterward, so results reflect the whole program. Return to eating after a fast is a recognized medical risk point, covered under safety.

Conditions named by fasting clinicians

The 2013 expert panel lists rheumatic diseases, chronic pain syndromes, hypertension, metabolic syndrome and other chronic conditions as indications it considers suitable for fasting therapy, and a related review by two of its members says medically supervised modified fasting is efficacious for several of these on the basis of empirical and observational evidence. These are positions of clinicians who practice and teach fasting therapy, and they cover modified fasting more than water-only fasting.

Proponents also describe fasting as a way to start lifestyle change, with the panel proposing that fasting-induced mood enhancement may support adoption of a healthier diet. This is a hypothesis stated in a review and not a tested finding.

Fasting as a start to diet change

The authors of the US hypertension studies describe medically supervised water-only fasting as a means of lowering blood pressure and prompting health-promoting behavior change. The studies are uncontrolled and the authors are affiliated with the centers that provide the program, as discussed under research.

Rheumatoid arthritis

A 2001 systematic review found 31 reports of fasting studies in rheumatoid arthritis. Only four controlled studies followed patients for at least three months after fasting, and pooling them showed a statistically and clinically significant long-term benefit for fasting followed by a vegetarian diet. The authors concluded that more randomized long-term studies were needed. Only the abstract was available to the page author, and the review predates current methods standards.

The 2013 review by Michalsen and Li states that benefit of fasting followed by a vegetarian diet in rheumatoid arthritis is supported by randomized controlled trials, and the expert panel reports the highest level of evidence for rheumatic diseases. These claims concern fasting plus a plant-based diet, and the studies used modified fasting, so they should not be read as evidence for prolonged water-only fasting alone.

Hypertension: uncontrolled series

A 2001 series of 174 consecutive inpatients with high blood pressure treated with medically supervised water-only fasting followed by a plant-based diet reported that almost 90% reached a reading under 140/90 mm Hg by the end of the program, with an average fall of 37/13 mm Hg. There was no comparison group. The first author owns the center, and only the abstract was reviewed.

A 2024 single-arm trial of 29 adults with stage 1 or 2 hypertension in a residential center reported median blood pressure of 135/81 mm Hg at baseline, 125/84 at the end of the fast and 114/78 at the end of refeeding. All 15 participants on antihypertensive medication were tapered off it during the program, and only 59% returned at 12 months. The authors list the absence of a control group and possible selection bias as limits, and one author owns the center.

Safety and wellbeing in a large clinic cohort

A one-year observational study at a German fasting clinic followed 1,422 adults and reported improved emotional and physical wellbeing, with most participants reporting no hunger. There was no control group, data were collected by clinic staff and the authors state the findings may apply only to that clinic and not to other facilities or to unsupervised fasting. Clinic physicians are among the authors.

Overall certainty

The verified sources contain no large randomized trial of prolonged water-only fasting against a sham or usual-care comparator, and no systematic review of water-only fasting specifically was found in a PubMed search for prolonged fasting systematic reviews. Evidence is mostly uncontrolled and from programs run by the groups that study them. Certainty for any outcome is low, and evidence for rheumatoid arthritis concerns a different, modified form.

Reactions and adverse events reported

In the German clinic cohort of 1,422 adults, adverse effects were reported in under 1%, including cardiac arrhythmia (0.21%), low sodium (0.21%) and low blood sugar (0.14%), and two participants (0.14%) were hospitalized. No deaths or permanent adverse effects were recorded. Among 1,311 who returned a symptom questionnaire, sleep disturbance was the most common mild symptom (14.94%).

In the US water-only trial, 453 adverse events were recorded among 29 participants: 84% grade 1, 14% grade 2 and 2% grade 3. Seven of the eight grade 3 events were hypertensive readings that resolved before the end of refeeding, and there were no serious adverse events. The expert panel lists circulatory dysregulation, mild low blood sugar, electrolyte disturbance and muscle cramps as expected reactions. These figures come from supervised settings and do not describe unsupervised fasting.

Refeeding syndrome

Refeeding syndrome is a recognized complication when food is reintroduced after a period of undernutrition. A consensus statement from the American Society for Parenteral and Enteral Nutrition defines it by falls in blood phosphorus, potassium or magnesium, or by organ dysfunction or thiamin deficiency, within five days of reintroducing calories. A systematic review of 35 observational studies in hospital patients found incidence ranging from 0% to 62% depending on definition and population and judged summary figures not meaningful. These data concern hospital patients, and no source gives a rate for fasting clinics.

Who is advised not to fast

The 2013 expert panel lists as contraindications cachexia, anorexia nervosa and eating disorders, uncontrolled hyperthyroidism, advanced cerebrovascular insufficiency or dementia, advanced liver or kidney insufficiency, and pregnancy and nursing. It lists addictions, type 1 diabetes, psychotic disorders, unstable coronary artery disease, retinal detachment, ulcer and cancer as conditions needing guidance by an experienced physician. It also names antidiabetic, antihypertensive and anticoagulant drugs among medications needing adjustment.

The German cohort enrolled only adults, and the sources reviewed give no recommendations for children. NHS Scotland material on Ramadan fasting for people using insulin warns of low blood sugar, dehydration and sudden kidney failure. The sources reviewed do not report gallstones, loss of lean mass or deaths from fasting, so those are not assessed here. This page is not a substitute for medical advice, and fasting should not delay or replace necessary care.

Training and standards

In Germany, a medical society for fasting and nutrition grants a training certificate in fasting therapy to physicians who meet its criteria, and some institutions train nonmedical fasting guides. These are the field's own professional arrangements, described in a guideline written by their members, and have not been independently audited. No registry or standard applying outside Germany was found, and legislation was not researched.