Therapeutic fasting (Buchinger): tradition, data — and the honest limits

Therapeutic fasting in the tradition of Otto Buchinger is a multi-day, severely calorie-reduced retreat: typically 4 to 21 days on around 200 to 250 kilocalories daily from vegetable broth, juices and a little honey, plus plenty of water and tea, accompanied by rest, movement and a structured setting — classically in specialised clinics or under the guidance of fasting physicians. That makes it something fundamentally different from intermittent fasting, which merely organises daily eating times and lets normal life continue.

This difference is the most important sentence of the article: intermittent fasting is an everyday tool — therapeutic fasting is a medically framed exception. Days of calorie withdrawal change fluid and electrolyte balance, blood pressure, uric acid and the effect of many medications. That is exactly why this article deliberately describes no do-it-yourself schedule: whether, how long and with what supervision someone fasts is a decision made with a doctor experienced in fasting.

The best available data source is the observational study from the Buchinger Wilhelmi clinic (2019): 1,422 participants, fasting periods of 4 to 21 days under medical supervision. Result: good tolerability, no serious incidents in the vast majority, falling blood pressure and blood glucose during the retreat, increased well-being. That is an honest safety signal for the supervised setting — but no more: without a control group and long-term follow-up, the study proves no healing effect, and values that fall during a 250-calorie week say nothing about three months later.

The new wave of trials since 2020: German fasting research around Andreas Michalsen (Charité/Immanuel Hospital Berlin) and the Buchinger Wilhelmi group has taken the important step from observations to randomised trials — with mixed, honest results. The strongest signal is the blood pressure trial by Maifeld and colleagues (2021, see above). The Buchinger Wilhelmi group's own first randomised trial (2026, a 5-day at-home fasting programme) confirmed safety and short-term metabolic improvements — the authors themselves call the effects “transient”. The two largest disease trials, by contrast (metabolic syndrome with 145 participants, rheumatoid arthritis/NutriFast), missed their primary endpoints. In short: the research is getting better — and so far it confirms both things: that fasting under supervision is feasible and much improves during the retreat, and that proof of lasting healing effects is still outstanding.

The Russian fasting tradition, which people often ask about: from the 1950s the Soviet Union treated thousands of people with “dosed fasting” (RDT) under Yuri Nikolaev, partly at state expense — a historically remarkable programme. The honest source situation: almost none of it is accessible in international peer-reviewed literature — essentially one English-language survey report from 1977; controlled trials from this tradition do not exist in the databases. That does not devalue the experiences, but it makes them scientifically unverifiable — exactly the difference between tradition and evidence that runs through this article.

The review by Michalsen and Li (2013) remains a worthwhile starting point. For the mechanisms side: the basic science on fasting, metabolic switching and cellular programmes is honestly assessed in the autophagy article — and there, too: lab enthusiasm is not human evidence.

One development deserves its own paragraph: the fasting-mimicking diet (FMD) — a multi-day, severely calorie-reduced special diet that “mimics” fasting for the body, developed around Valter Longo's group. Randomised trials are now running in serious medical contexts: in breast cancer patients undergoing chemotherapy, FMD improved tumour response to therapy in the DIRECT trial (2020) without increasing side effects; in mild-to-moderate Crohn's disease, a randomised trial in Nature Medicine (2026) showed higher response and remission rates than the comparison diet. At the same time, a 2023 meta-analysis found no evidence that fasting generally prevents chemotherapy side effects — the field is young and the results are mixed.

The framing in full clarity: these are results from strictly medically supervised trial settings — not instructions, and certainly no reason to fast on your own with an illness. Anyone with one of these diagnoses who is interested in FMD discusses it exclusively with their own care team. For this magazine, FMD is above all one thing: proof that serious fasting research is getting more exciting — we are watching the field and will update as the evidence consolidates.

No therapeutic fasting — the exclusions consistently named in the literature: a history of eating disorders (multi-day fasting is a known trigger), underweight and malnutrition, pregnancy and breastfeeding, children and adolescents, type 1 diabetes, and advanced liver or kidney disease.

Only with a medical decision and supervision: type 2 diabetes with medication and, in general, any long-term medication (blood pressure drugs, anticoagulants, psychotropics — doses can shift considerably during fasting), a history of gout (fasting raises uric acid and can trigger attacks), cardiovascular disease, older age with low muscle reserves.

And the limit that applies to healthy people too: anyone working normally, driving, training and caring for a family during a multi-day fast is not practising a fasting tradition but running an uncontrolled experiment. The tradition that therapeutic fasting invokes has always understood withdrawal from everyday life as part of the retreat.

Therapeutic fasting can be an intense experience that some people value — as a conscious, medically supervised retreat with realistic expectations: a reset for habits, distance from constant eating, for many a strong experience of self-efficacy. What it is not, on today's evidence: a proven therapy, a weight-loss method, or a "detox" (your liver and kidneys handle that daily, free of charge).

That is why it is deliberately not a feature in our app: we support intermittent fasting as an everyday tool — multi-day fasting retreats belong in experienced medical hands, not in an unsupervised app. And perhaps the most honest question before any fasting week: are you looking for a retreat — or actually for a way of eating you can sustain all year? For the latter, the unspectacular path is the more effective one.