Buchinger Therapeutic Fasting: How It Works, What Studies Show and Who It Suits
Vegetable broth, juice, a little honey and plenty of water. Buchinger fasting is not a pure water fast, but a supervised fast with around 250 kilocalories a day. Here you can read what happens inside you, what studies show and when you are better off not fasting alone.
Therapeutic fasting is often described as spring cleaning for body and soul. I see it as a medical tool that deserves to be taken seriously. A tool does not get better when you romanticize it. It gets better when you know when it fits and when it does not.
It is early March. A message pops up in your group chat: fasting week starting Monday, who's in? Three thumbs up, two hearts. Someone writes that this is her fresh start every spring.
Your circle of friends has made plans. Someone sends a recipe for vegetable broth, someone else a list of herbal teas. There is laughter and planning, and it feels a bit like a new beginning.
And you sit in the middle of it, quietly running the numbers in your head. Maybe you take something for your blood pressure. Maybe your vision sometimes goes black for a moment when you stand up quickly. Nobody in the group asks about it, and you don't dare to bring it up.
This article was written for exactly that moment. Not to talk you out of fasting. But so that you know what ground you are starting on.
This uncertainty is not a sign of weakness. It is a smart question. Can I do this? What will my circulation, my pills, my blood pressure do? These questions deserve an honest answer instead of fasting romanticism.
What you can expect in this article
- How Buchinger fasting differs from water fasting
- How relief days, fasting days and refeeding days work
- What ketosis, salt and water do to your circulation
- What 1422 and 1610 people fasting reveal about blood pressure and safety
- What randomized trials show and what remains open
- Who should fast only under medical supervision, or not at all
- The KPNI view of a fasting week
- Three levers for your decision
How I label the evidence
Clinical study Randomized trials in humans. They carry the most weight, but in therapeutic fasting they are usually small.
Human observation Cohorts, physiological studies, reviews and consensus papers. They show associations and mechanisms, not necessarily cause and effect.
Animal studies and cell studies play no role in this article. All the data cited come from humans.
What is Buchinger therapeutic fasting, and how does it differ from water fasting?
In short: Buchinger therapeutic fasting is a modified fast. Instead of water alone, you have a little vegetable broth, juice and honey every day, together around 200 to 250 kilocalories. The fasting period is framed by relief days before and refeeding days after.
When you think of therapeutic fasting, you may picture a glass of water and a week of hunger. Many people have exactly this image in mind. For Buchinger fasting, it is only half true.
The method is named after the physician Otto Buchinger, who made it known around a hundred years ago. Fasting for medical purposes has a long tradition in Europe. Today it is used in specialized fasting clinics and in departments of integrative medicine.
The German guideline on therapeutic fasting describes fasting as voluntarily going without solid food and stimulants for a limited time. You drink at least two and a half liters of calorie-free fluid a day, meaning water and herbal tea. In classic Buchinger fasting, vegetable broth, fruit or vegetable juice and a little honey are added.
Vegetable broth
Usually in the evening and warm. It brings salt and minerals from the vegetables into a day without solid food.
Juice
From fruit or vegetables, usually at midday. It supplies part of the small amount of carbohydrate.
Honey
A few teaspoons, for example in tea. The guideline names at most two to three teaspoons a day.
Water and tea
At least two and a half liters of calorie-free fluid a day are meant to support your circulation and kidneys.
In the large observational study from the Buchinger Wilhelmi clinic, this added up to an energy intake of 200 to 250 kilocalories a day. That is not much. But it is not nothing, and this small remainder is exactly what makes the difference from water fasting.
Expert consensus In 2024, in Cell Metabolism, Daniela Koppold and an international team around Charité Berlin standardized the technical terms used for fasting. Over several rounds of surveys, 38 experts from research and clinical practice reached agreement.
They define modified fasting as limiting energy intake to at most 25 percent of requirements. Prolonged fasting means fasting for four or more consecutive days.
What this means for you: Buchinger fasting is a modified and usually prolonged fast. It can only be compared to a limited extent with water fasting or 16:8.
Koppold DA et al. Cell Metab. 2024. DOI: 10.1016/j.cmet.2024.06.013Buchinger fasting
- around 200 to 250 kilocalories from broth, juice and honey
- some salt from outside via the broth
- ketosis sets in, usually somewhat milder
- set phases: relief, fasting, breaking the fast, refeeding
- in the large studies, with an exercise program and supervision
Water fasting
- no calories, only water or unsweetened tea
- no salt from outside
- ketosis usually more pronounced
- higher demands on monitoring circulation and lab values
- more on this in the article Water Fasting: Potential Benefits and Risks
Buchinger fasting is not starving with exceptions. It is fasting with a handrail. Broth, juice and honey are not cheating. They are part of a protocol designed to cushion the transition into fasting metabolism.
And now you know why Buchinger fasting is a genuine fast despite the juice and honey.
How does a Buchinger fasting week work?
In short: According to the guideline, the fasting week for healthy people lasts eight days: one relief day, five fasting days, two refeeding days. Under medical supervision, people often fast for seven to ten days, followed by three refeeding days.
Maybe you picture a fasting week like a light switch. Off on Monday, back on by Sunday. That is not how your metabolism works. It needs ramps, not toggle switches.
Imagine a staircase leading into a lake. The relief days are the steps down. The fasting days are the swimming. The refeeding days are the steps back up. And the supervision is the handrail.
Relief days
One to two days of light, mainly plant-based food. For the preparation day, the guideline names less than about 1000 kilocalories, without coffee, alcohol and nicotine.
Fasting days
Five days for healthy people, often seven to ten under medical supervision. Broth, juice, honey, plenty of water and herbal tea, plus exercise and rest.
Breaking the fast
On the last fasting day, a ripe apple is traditionally eaten, raw or steamed, and very slowly.
Refeeding days
Two to four days in which the amount of energy increases step by step. The guideline describes about 800, 1000, 1200 and 1600 kilocalories.
This is how the 2013 guideline on fasting medicine describes it. For healthy people, it names a fasting week of eight days. For medically supervised therapeutic fasting, the Ärztegesellschaft Heilfasten und Ernährung, a German medical society for therapeutic fasting and nutrition, recommends seven to ten fasting days, one preparation day and three refeeding days.
Expert consensus In 2013, Françoise Wilhelmi de Toledo, Andreas Michalsen and other experts in fasting medicine updated the German consensus guidelines on therapeutic fasting from 2002. They describe the definition, procedure, accompanying measures and safety standards.
They see the strongest evidence in rheumatic diseases. For metabolic diseases, pain syndromes, high blood pressure and other chronic conditions, they speak of preliminary clinical and observational data.
What this means for you: the fasting week is not a made-up protocol, but described and standardized. The guideline requires that fasting treatments be supervised by physicians or therapists trained in fasting therapy.
Wilhelmi de Toledo F et al. Forsch Komplementmed. 2013. DOI: 10.1159/000357602Relief days: braking before the bend
The relief days are like braking before a bend. Smaller portions, more vegetables, hardly any sugar, no alcohol. If you drink a lot of coffee, giving it up often shows up as a headache. If this withdrawal falls on the relief days, starting the fast may be easier.
There are hardly any dedicated studies on the benefit of relief days. They are clinical tradition, but physiologically well founded. In the randomized Berlin study on fasting in metabolic syndrome, the fast was also preceded by two calorie-reduced vegan days.
Bowel cleansing: tradition with a question mark
In the clinics where the large Buchinger studies come from, a laxative was part of the start of the fast. Whether this is necessary for the benefit of fasting has hardly been studied. What is clear, however, is that laxatives cost additional water and salt. If you tend toward low blood pressure, discuss this step with a physician beforehand.
Breaking the fast and refeeding days: why the ramp matters
On the last fasting day, you traditionally eat a ripe apple, raw or steamed. Slowly, bite by bite. That is a ritual. But it is also a gentle first stimulus for your stomach, gut and pancreas.
When you eat, insulin rises again. And insulin has a job that hardly anyone thinks about: it holds on to salt in the kidneys.
Human physiology In 1975, in the Journal of Clinical Investigation, Ralph DeFronzo and colleagues studied six healthy people to see what insulin does to salt excretion by the kidneys. Blood glucose was held constant during the experiment.
Under insulin, urinary sodium excretion fell from 401 to 213 microequivalents per minute. Less potassium and phosphate were excreted as well, and blood potassium fell.
What this means for you: insulin is something like a salt keeper. When it falls during fasting, more salt and water can be lost. When it rises again with eating, the body tends to hold on to both.
DeFronzo RA et al. J Clin Invest. 1975. DOI: 10.1172/JCI107996That is why the scale often shows a little more again in the first refeeding days. This is usually retained water, not fat. At the same time, more potassium and phosphate can move into the cells. In severely malnourished people, this surge can become dangerous. Experts then speak of refeeding syndrome.
The ASPEN consensus recommendations define it by a drop in phosphate, potassium or magnesium within five days of restarting calorie intake. They were developed for people in hospital, not for healthy people who fast. But the principle explains why refeeding after a fasting week should not be a feast. You can read how to plan your first meal in the article Breaking a Fast Properly.
Schematic: energy per day in a Buchinger week
Orientation based on the 2013 guideline and the clinical studies. Not an individual plan: how many refeeding days make sense depends on how long you fast and on your health.
What is often underestimated during the refeeding days
- Blood pressure can stay low. In the cohort of 1610 people fasting, the reduction persisted during the four refeeding days, even in people who had stopped their blood pressure medication.
- Reduced medications should be reviewed by a physician before they are restarted, not by gut feeling.
- Small portions, slow eating and thorough chewing give your gut time to power back up.
- A quick rise on the scale in the first refeeding days is usually water.
Many people see the fasting days as the main course and the refeeding days as an afterthought. Physiologically, both deserve the same attention. During the refeeding days, the body readjusts to eating. And that is where it is decided whether a week turns into a habit.
And now you know why a good fasting week is planned backward from the refeeding days, not forward from the first fasting day.
What happens in your body during therapeutic fasting? Ketosis, electrolytes and blood pressure
In short: After about one to two days, the liver's sugar stores are largely empty. Insulin falls, the kidneys release more salt and water, and the liver produces ketone bodies. Blood pressure often falls, and for many people hunger subsides.
Day two. Your head feels tight, your vision flickers briefly when you stand up, the night was restless. Day four. You wake up, and your hunger is surprisingly quiet. Many people experience exactly this curve. There is an explanation for it.
Imagine your energy supply like your finances. The sugar in your blood is the loose change in your pocket. The glycogen in your liver and muscles is your checking account, and it lasts about one to two days. Your fat tissue is your savings account, and in most people it is well stocked.
During fasting, the checking account runs dry first. Then your body transfers money from the savings account. The liver builds ketone bodies from fatty acids, a currency your brain accepts too. George Cahill of Harvard Medical School researched this switch for decades. He describes that it was only the brain's use of the ketone body beta-hydroxybutyrate that made it possible for humans to survive longer periods of starvation.
Sugar stores empty
In the first one to two days, the liver releases its glycogen reserves. A lot of exercise can speed this up.
Insulin falls
Without significant carbohydrates, insulin drops to a low level. The fat stores open up.
Salt and water leave
As insulin falls, the kidney's salt brake loosens. The scale drops quickly, and blood pressure often does too.
Ketone bodies rise
The liver builds ketone bodies as fuel, including for the brain. In the Buchinger cohort, they were detectable in the urine of more than 95 percent from day four onward.
A new balance
For many people, hunger subsides and circulation settles. For some, dizziness, headaches or restless sleep remain.
Human observation In 2024, in Nutrients, Franziska Grundler and the team at the Buchinger Wilhelmi clinic in Überlingen tracked the daily ketone levels of 1610 people. They fasted for 4 to 21 days following the Buchinger program.
From day four onward, ketone bodies were detectable in the urine of more than 95 percent. Those who had only broth without juice and honey took in 72 instead of 236 kilocalories. Carbohydrates fell from 56.5 to 15.6 grams, and ketosis was more pronounced. It never reached pathological levels, but with strong ketosis, uric acid rose more.
What this means for you: juice and honey do not prevent ketosis, they dampen it. Fasting ketosis is something different from the dangerous ketoacidosis of uncontrolled diabetes, with which it is often confused.
Grundler F et al. Nutrients. 2024. DOI: 10.3390/nu16121849Salt, water and blood pressure
At the same time, your salt balance shifts. When insulin falls, the salt brake in the kidney loosens. In the first days, you can therefore lose more sodium and water. Blood volume becomes somewhat smaller, and blood pressure falls.
The authors of the large blood pressure study from the Buchinger clinic name this increased salt excretion as one possible reason for the drop in blood pressure. Added to this are lower activity of the sympathetic nervous system and the weight loss.
This is where the broth comes in. It brings back a little salt every evening. In the cohort of 1422 people fasting, blood sodium fell slightly, but on average stayed in the normal range. Individual cases of mild sodium deficiency were balanced with table salt.
The dizziness when you stand up quickly can have its roots right here. Less salt, less volume in your blood vessels, a circulation that has to readjust. Standing up slowly during the fasting period is therefore not an empty phrase, but protection.
The nervous system: first the gas, then the brake
Human observation In 2025, in the International Journal of Obesity, Robin Mesnage and colleagues analyzed the daily heart rate variability of 16 people. They fasted for twelve days following Buchinger on around 250 kilocalories, and measurements were also taken one week before and after.
In the early fasting phase, the activity of the sympathetic nervous system, the gas pedal of your nervous system, rose at first. Over the whole period, parasympathetic activity, the brake, then increased, and emotional well-being improved. Sleep quality remained unchanged.
What this means for you: the exhausting first days could partly be a brief stress response. After that, the nervous system seems to switch to a calmer mode in many people. The analysis is small and exploratory, and larger randomized trials are lacking.
Mesnage R et al. Int J Obes. 2025. DOI: 10.1038/s41366-025-01843-0And hunger? In the cohort of 1422 people fasting, 93.2 percent reported feeling no hunger during the fast. For many, this is the biggest surprise of the week. For some, though, the hunger stays, and that is not a failure.
The dizziness on day two is not a test of character. It is circulatory physics. Less salt, less volume, a system finding a new balance. That is exactly what the broth, standing up slowly and supervision that keeps an eye on blood pressure and well-being are for.
And now you know why the mug of broth in Buchinger fasting is more care for your circulation than a meal.
What do studies on therapeutic fasting show about blood pressure and safety?
In short: Large observational data from fasting clinics show good tolerability and marked reductions in blood pressure, especially when starting values are elevated. Randomized trials are small and short. How long the effects last without a change in diet remains open.
Maybe you have heard that therapeutic fasting lowers blood pressure. Maybe also that it is dangerous. Both fall short. The data tell a more nuanced story.
For high blood pressure, conventional medicine rightly relies on exercise, nutrition, less salt and, where necessary, medication. From an integrative perspective, therapeutic fasting can be an additional building block. It is not a replacement for treatment.
Human observation In 2019, in PLoS One, Françoise Wilhelmi de Toledo and colleagues documented 1422 people at the Buchinger Wilhelmi clinic over the course of one year. They fasted for 4 to 21 days on 200 to 250 kilocalories a day, accompanied by a moderate exercise program.
Weight, waist circumference and blood pressure fell, blood glucose dropped into the low normal range, and ketone bodies rose. A total of 93.2 percent felt no hunger, and of 404 people with pre-existing complaints, 341 reported an improvement. Adverse effects occurred in less than one percent.
What this means for you: in a clinical setting, Buchinger fasting appears to be well tolerated by most people. There was no control group, however.
Wilhelmi de Toledo F et al. PLoS One. 2019. DOI: 10.1371/journal.pone.0209353Human observation In 2020, in the Journal of the American Heart Association, Franziska Grundler, Andreas Michalsen and colleagues analyzed the daily blood pressure readings of 1610 people. They fasted for 4 to 41 days on about 250 kilocalories.
On average, blood pressure fell by 6.5/3.8 mmHg. In untreated high blood pressure, it was 16.7/8.8 mmHg, with readings above 160/100 mmHg even 24.7/13.1 mmHg, and with normal blood pressure only 3.0/1.9 mmHg. In the group taking blood pressure medication, it was stopped in 23.6 percent and reduced in 43.5 percent.
What this means for you: therapeutic fasting seems to lower blood pressure mainly where it is elevated. If you take blood pressure medication, you therefore need supervision that adjusts the dose in time.
Grundler F et al. J Am Heart Assoc. 2020. DOI: 10.1161/JAHA.120.018649What randomized trials show so far
Observational data have one weakness. Without a comparison group, it remains open how much is due to the fasting and how much to rest, exercise and clinic routine. Randomized trials on therapeutic fasting are still rare. The few that exist are small, but revealing.
RCT In 2021, András Maifeld, Dominik Müller, Andreas Michalsen and colleagues from Berlin published a randomized trial in Nature Communications. They randomly divided 71 people with metabolic syndrome and high blood pressure into two groups. One group fasted for five days and then ate according to the DASH principle, a diet geared toward healthy blood pressure with plenty of vegetables and little salt. The other group followed DASH only.
Three months later, systolic blood pressure and body mass index were lower in the fasting group than with DASH alone, and the need for blood pressure medication had decreased more. In addition, the gut microbiome changed, including bacterial groups linked to the production of short-chain fatty acids.
What this means for you: a short fast before a change in diet could achieve more than the change alone. The study was small, and the results on the immune system and microbiome were exploratory endpoints.
Maifeld A et al. Nat Commun. 2021. DOI: 10.1038/s41467-021-22097-0Similarly small, but randomized, was a 2017 pilot study by Chenying Li and the team around Andreas Michalsen at Charité. The 46 participants had type 2 diabetes and were taking tablets or insulin. They either fasted for seven days following Buchinger on 300 kilocalories a day or received usual care with nutritional counseling, and 32 completed the study. After four months, the fasting group had lost more weight, 3.5 versus 2.0 kilograms, and blood pressure and quality of life improved more clearly. For the long-term blood sugar marker HbA1c, insulin and the HOMA index, there were only improvements that did not reach statistical significance, and no serious side effects occurred.
Rheumatoid arthritis: the most thoroughly studied field
RCT In 1991, the team around Kjeldsen-Kragh at the University of Oslo published a randomized, single-blind trial with 53 people with rheumatoid arthritis in the Lancet. Of these, 27 first fasted for seven to ten days on very little energy and then ate a vegetarian diet for one year, while 26 continued to eat as usual.
After four weeks, the fasting group showed improvements in joint swelling, pain, morning stiffness, grip strength and inflammatory markers such as CRP, among other things. The advantage was still present after one year.
What this means for you: in rheumatoid arthritis, fasting is among the most thoroughly studied applications. However, the authors point out that most people relapse after fasting alone as soon as they return to eating normally.
Kjeldsen-Kragh J et al. Lancet. 1991. DOI: 10.1016/0140-6736(91)91770-uIn 2001, a systematic review by Müller, de Toledo and Resch found a total of 31 reports on fasting studies in rheumatoid arthritis. Only four of them were controlled and had at least three months of follow-up. Taken together, they showed a clinically relevant long-term effect, but the authors explicitly called for more randomized long-term studies.
A more recent study puts this picture into perspective. In 2022, Anika Hartmann and colleagues at Charité studied 53 people with rheumatoid arthritis. They compared a fasting week followed by a plant-based diet with the recommendations of the German Nutrition Society. For the primary endpoint, everyday function after twelve weeks, there was no significant difference. The fasting group, however, improved faster and lost more weight, 3.9 versus 0.7 kilograms.
How long do the effects last?
In 2024, in Nutrition Reviews, Mark Ezpeleta, Krista Varady and colleagues at the University of Illinois Chicago summarized human studies on prolonged fasting. They looked at fasting periods of 5 to 20 days. Blood pressure fell consistently, and weight fell by 2 to 10 percent, about two thirds of which was fat-free mass. Three to four months after the fast, the metabolic benefits were no longer detectable in the studies that checked this, even when weight was maintained.
Two new randomized trials from 2026 fit this picture. In a study by the Buchinger Wilhelmi clinic, 64 healthy people either fasted at home for five days, in a modified form with around 600 kilocalories, or continued living as usual. Blood pressure fell significantly more than in the control group only after food was reintroduced. One month later, the changes in blood metabolic markers and gut flora no longer differed significantly from the control group. In the Berlin LEANER study with 38 healthy adults, a five-day fast led mainly to fat loss, which was partly maintained after twelve weeks.
| Claim | Evidence | Assessment |
|---|---|---|
| Blood pressure falls during fasting, especially when it is elevated | Large cohorts with 1422 and 1610 people fasting, small randomized trials | well supported for the fasting phase |
| Buchinger fasting is well tolerated under supervision | Cohorts with adverse effects below one percent | well supported in a clinical setting |
| Long-term benefit in rheumatoid arthritis | RCT from 1991, systematic review, newer RCT without an advantage in the primary endpoint | supported with limitations |
| Effects last for months even without a change in diet | Review: no longer detectable after three to four months | rather not supported |
| Relief days, bowel cleansing, an apple to break the fast | hardly any dedicated studies | clinical tradition |
The large cohorts come from the same clinic, and many of the authors work there. That does not make the data wrong. But it is a reason to read them as observation.
Observational studies show a temporal association, not proof of cause and effect. People who can afford and want a week in a fasting clinic probably bring different starting conditions than the average person. And rest, exercise and distance from everyday life are always part of the package there.
Therapeutic fasting is not a permanent state. It is more of a starting push than a result. The studies with the most lasting effects combined fasting with a change in diet, not with a return to old habits.
And now you know why the most exciting question in therapeutic fasting is not the fasting week, but the time after it.
Who is therapeutic fasting suitable for, and who should not fast alone?
In short: Healthy adults without long-term medication can consider a fasting week with trained guidance. With medication or pre-existing conditions, therapeutic fasting belongs under medical supervision. In eating disorders, severe underweight, pregnancy, breastfeeding and some serious illnesses, the guideline advises against it altogether.
Maybe this is the question that brought you here. It is the most important one in this article. Because the answer is not about your courage, but about the right setting.
The guideline describes fasting for healthy people as being for those who feel well, need no medication and are emotionally stable. For them, a fasting week alone or in a group is conceivable, usually guided by a trained fasting instructor. The responsibility always remains with you.
Rather suitable, with guidance
- healthy adults who feel well
- no long-term medication
- emotionally stable, no history of eating disorders
- time for rest, exercise and refeeding days
Only with medical supervision
- blood pressure medication or other long-term medication
- diabetes, especially type 1 or with insulin
- gout or elevated uric acid
- coronary heart disease, especially if unstable or severe
- cancer, a stomach or duodenal ulcer, retinal detachment
- addiction or a psychotic disorder
Do not fast
- wasting or severe underweight
- anorexia and other eating disorders
- uncontrolled overactive thyroid
- advanced liver or kidney insufficiency
- advanced circulatory disorder of the brain or dementia
- pregnancy and breastfeeding
Compiled from the 2013 guideline on therapeutic fasting, supplemented with notes from the studies on blood pressure, ketosis and diabetes. This overview does not replace a medical assessment.
Blood pressure medication and low blood pressure
In the cohort of 1610 people fasting, blood pressure medication had to be reduced or stopped in many people to avoid readings that were too low. Without medical adjustment, blood pressure can fall too low, with dizziness and a risk of falls. Conversely, blood pressure rose slightly in 69 women with starting values below 100/60 mmHg. Whether they had any symptoms is not known.
Eating disorders: why fasting is no experiment here
Eric Stice and colleagues at the Oregon Research Institute followed 496 adolescent girls over five years. Girls who went a whole day without eating to control their weight were more likely to develop binge eating and bulimic symptoms during this period. Fasting usually predicted this more strongly than dieting alone, although the difference was significant in only some of the comparisons. What this means for you: if you have ever had an eating disorder, a fasting week is not a harmless fresh start.
Diabetes, gout and medication
If you take insulin or tablets that lower blood sugar, fasting changes the conditions under which these medications were dosed. In the randomized Charité study on type 2 diabetes, no serious side effects occurred. However, that was a controlled study setting, not fasting on your own. For type 1 diabetes, the guideline requires experienced medical supervision.
With gout or elevated uric acid, it is worth checking your levels before you start. In the Buchinger cohort, uric acid rose more with stronger ketosis. This argues for planning the fast with a physician in this case.
Not being allowed to fast is not a defeat. It is information about your body. For many people there are gentler paths, such as a longer overnight break from eating, as in intermittent fasting, or medically supervised fasting in a setting that suits your health.
Self-check before the fasting week
- I take medication regularly, for example for high blood pressure or diabetes, or water pills.
- I often feel dizzy or my vision goes black when I stand up quickly.
- I have had a gout attack before or know that my uric acid is elevated.
- I have had an eating disorder at some point, or my relationship with food is difficult.
- I am pregnant or breastfeeding.
- I am clearly underweight or have recently lost weight without trying.
- I have a heart, kidney, liver or thyroid condition.
- I am currently in an emotional crisis or a very stressful phase.
If you nod at any of these points, that is first of all a yes to a conversation with a physician before the first fasting day. In pregnancy, breastfeeding, eating disorders or severe underweight, the guideline advises against fasting altogether.
And now you know why the most important preparation for a fasting week does not happen in the supermarket, but in conversation.
How does KPNI view therapeutic fasting?
Clinical Psychoneuroimmunology does not only ask what a single organ does. It asks how the nervous system, hormones, metabolism and immune system talk to each other. During therapeutic fasting, these four have a particularly lively conversation.
Nervous system
In the first fasting days, the sympathetic nervous system, the gas pedal, can briefly kick in. After that, a small Buchinger study showed more parasympathetic activity and better emotional well-being. In the large blood pressure cohort, stress scores also fell.
Hormonal system
Insulin falls, and with it the salt brake in the kidney loosens. The fat stores open up, and the liver produces ketone bodies. For people on insulin or blood pressure medication, this is crucial, because their medication needs can change within a few days.
Metabolism
Ketone bodies become a second fuel, including for the brain. With stronger ketosis, uric acid rose more in the Buchinger cohort, possibly because ketone bodies and uric acid compete for similar excretion pathways in the kidney. Juice and honey dampen ketosis without preventing it.
Immune system
In the Oslo rheumatoid arthritis study, inflammatory markers such as CRP fell with fasting followed by a vegetarian diet. An analysis of the Buchinger cohort describes a pattern that depends on the starting value: with high CRP, the value tended to fall, and with low CRP, it tended to rise slightly during fasting. This points more to a recalibration than to simple dampening, but it has been little studied so far.
From the perspective of lifestyle medicine, there is a fifth level. In their review, Andreas Michalsen and Chenying Li of Charité describe how fasting could make it easier to start eating a healthier diet in the long run. They suspect that the better mood many people experience during fasting plays a role in this. What this means for you: a fasting week can be a window in which change comes more easily.
Well supported by large observational data and small randomized trials: during fasting, blood pressure falls, especially when it is elevated. Ketosis sets in despite broth, juice and honey. Under clinical supervision, adverse effects were rare in the large cohorts.
Mechanistically plausible, still thin in humans: that increased salt excretion and a calmer sympathetic nervous system explain the blood pressure effect, and that the immune system recalibrates differently depending on the starting point.
Clinical tradition without a strong study base: relief days, bowel cleansing, the apple to break the fast and the exact number of refeeding days.
My assessment: for healthy people, a Buchinger week can be an exciting stimulus. For people with high blood pressure or metabolic problems, I see potential, but only with a plan for before, during and after.
Therapeutic fasting is not about three kilos on the scale. It is about the experience that your body has reserves and that you can trust it. This freedom does not come from holding out at any cost. It comes from a setting in which you are allowed to let go.
And now you know why I never see therapeutic fasting as just a diet, but as a conversation between four systems.
Three levers for your decision
You don't have to decide today whether you will fast. But you can decide today how you will make that decision. The following three levers are directions, not a treatment plan.
Clarify your starting point before you sign up
Have a physician look at your blood pressure, medication, kidney values and uric acid, especially if you take tablets or have had a gout attack before. Also speak openly about your relationship with food. This conversation is the most important part of your preparation.
Choose the setting based on your risk, not on the group
Healthy and without long-term medication? Then a fasting group with a trained fasting instructor can be a good setting. With pre-existing conditions or medication, the fasting week belongs under medical supervision, as an outpatient or in a clinic. You are welcome to join the fun without joining the fast.
Plan the weeks afterwards right away
The studies with the most lasting effects combined fasting with a change in diet, such as a vegetarian diet or one geared toward healthy blood pressure. Before the first fasting day, think about which habit you would like to keep afterwards. A single one is enough to begin with.
If you would like to do more than read and want to look at your situation together: below this article you will find the option to book an appointment.
And now you know why a good fasting week begins weeks in advance.
Frequently asked questions about Buchinger therapeutic fasting
What is Buchinger therapeutic fasting?
Buchinger therapeutic fasting is a form of modified fasting in which you go without solid food and stimulants for a limited time. Instead of water alone, you have about a quarter liter of vegetable broth, a quarter liter of fruit or vegetable juice and a little honey each day, plus at least two and a half liters of water and herbal tea. This is how the 2013 guideline on therapeutic fasting describes it. In large clinical studies, this added up to an energy intake of about 200 to 250 kilocalories a day. Relief days beforehand and refeeding days afterwards are an integral part of it.
How many calories does Buchinger fasting provide?
In the observational study with 1422 people fasting, intake was 200 to 250 kilocalories a day. An analysis of 1610 people fasting reports about 75 to 250 kilocalories, depending on the variant. Those who had only broth without juice and honey took in around 72 instead of 236 kilocalories and showed more pronounced ketosis. The guideline on therapeutic fasting sets the overall upper limit for fasting at about 250 to 500 kilocalories a day.
How long does a Buchinger fasting week last?
For healthy people, the guideline describes eight days: one relief day, five fasting days and two refeeding days. For medically supervised therapeutic fasting, the German medical society for therapeutic fasting and nutrition (Ärztegesellschaft Heilfasten und Ernährung) names seven to ten fasting days with one preparation day and three refeeding days. In the large clinical studies, people fasted for 4 to 21 days, and in the blood pressure study in some cases even longer. Longer fasting periods always belong under medical supervision.
What are relief days, and what are they good for?
Relief days are one to two days before fasting with light, mainly plant-based, low-calorie food. For the preparation day, the guideline names less than about 1000 kilocalories and going without coffee, alcohol and nicotine. They are meant to make the transition gentler, for example because coffee withdrawal then does not coincide with the first fasting days. There are hardly any dedicated studies on their benefit. They are mainly clinical tradition.
How do you break a Buchinger fast?
Traditionally, on the last fasting day you eat a ripe apple, raw or steamed, and very slowly. After that, the amount of energy increases step by step over several refeeding days, according to the guideline from about 800 to 1000 and 1200 up to 1600 kilocalories. The reason is physiological: when you eat, insulin rises, and insulin makes the kidneys hold on to sodium and lowers potassium in the blood. A slow reintroduction of food gives your body time to adjust.
Does therapeutic fasting lower blood pressure?
In large observational data, blood pressure falls markedly during fasting, especially when starting values are elevated. In a cohort of 1610 people fasting, it fell by an average of 16.7/8.8 mmHg in untreated high blood pressure, but only by 3.0/1.9 mmHg in people with normal blood pressure. A small randomized trial in metabolic syndrome found lower systolic blood pressure three months after five fasting days followed by a DASH diet than with DASH alone. How long the effect lasts without a change in diet remains open.
Is therapeutic fasting dangerous?
Under clinical supervision, Buchinger fasting appears to be well tolerated by most people. In the observational study with 1422 people fasting, adverse effects occurred in less than one percent. Possible mild complaints include headaches, hunger, sleep problems and dizziness when standing up quickly. It becomes risky mainly with pre-existing conditions, certain medications, low body weight or eating disorders, and with longer fasting without monitoring.
Who should not do therapeutic fasting?
The guideline lists the following contraindications: severe wasting, anorexia and other eating disorders, uncontrolled hyperthyroidism, advanced circulatory disorders of the brain or dementia, advanced liver or kidney insufficiency, as well as pregnancy and breastfeeding. Conditions in which fasting is only an option with experienced medical supervision include type 1 diabetes, addiction, psychotic disorders, unstable or severe coronary heart disease, retinal detachment, a stomach or duodenal ulcer and cancer. If you take medication regularly, you should also fast only under medical supervision.
Can I do therapeutic fasting while taking blood pressure pills?
Yes, but only with medical supervision. Because blood pressure can fall during fasting, blood pressure medication was stopped in 23.6 percent and reduced in 43.5 percent of the treated people in a cohort of 1610 people fasting. Without adjustment, blood pressure can fall too low, with dizziness and a risk of falls. Restarting the medication after the fast should also be planned with a physician.
Is Buchinger fasting the same as water fasting?
No. Water fasting provides no calories and no salt from outside. In Buchinger fasting, broth, juice and honey supply a small amount of energy, carbohydrates and salt every day. In an analysis of 1610 people fasting, this small amount of carbohydrate dampened ketosis without preventing it. According to the 2024 international consensus, this counts as modified fasting, because energy intake is limited to at most 25 percent of requirements.
How long do the effects of therapeutic fasting last?
That is the biggest open question. A review of prolonged fasting found that the metabolic benefits were no longer detectable three to four months later, even when weight was maintained. Effects lasted longer in studies that combined fasting with a change in diet, for example in rheumatoid arthritis with a vegetarian diet for one year. Therapeutic fasting can be a starting push, but it does not replace a lasting change in everyday life.
Do I lose muscle during therapeutic fasting?
Part of the weight loss is fat-free mass, but that also includes water and glycogen. In a study of 32 people who fasted for twelve days on 250 kilocalories, the volume of the calf muscles decreased by 5.4 percent. This largely matched the expected loss of glycogen and bound water, and muscle strength was preserved, including in participants over 50. For people with little muscle reserve, it is still a point for careful medical consideration.
Can I do therapeutic fasting alone at home?
For healthy people without medication, the guideline describes fasting alone or in a group, usually guided by a trained fasting instructor and always on your own responsibility. As soon as pre-existing conditions, medication or an eating disorder are involved, therapeutic fasting belongs under medical supervision. In a randomized trial with 64 healthy people, a five-day modified fast at home with around 600 kilocalories was described as safe. However, that was a structured study protocol with regular examinations.
More from the Fasting Guide
- Fasting for beginners: the gentle start
- Water fasting: potential benefits and risks
- Breaking a fast properly: the first meal
- The fasting mimicking diet (FMD) explained
- Intermittent fasting 16:8: what happens in the body
- Autophagy: when does it begin?
- Muscle loss during fasting
- Fasting, blood sugar and insulin resistance
- Fasting with type 2 diabetes
- Fasting and the gut microbiome
- Fasting and lifespan
- Fasting for women and the menstrual cycle
- Fasting during menopause
- Fasting with Hashimoto's
- Fasting with exhaustion
- Intermittent fasting and sleep
- Intermittent fasting and iron deficiency
- What breaks a fast?
- Cravings during intermittent fasting
Where this topic touches other areas
Therapeutic fasting touches on detoxification, the nervous system, exercise and the cardiovascular system. If you want to go deeper, these neighboring topics are worth a look.
Fasting, detoxification and autophagy
What fasting may have to do with detoxification and autophagy.
DetoxJuice cleanses and detox teas, critically examined
What juice cleanses and detox teas can and cannot do.
CleansingAlkaline diets and overacidification
A critical look at alkaline diets and cleansing.
Nervous systemBreathing techniques and the vagus nerve
How breathing can engage the parasympathetic nervous system.
ExerciseMoving after meals
A small lever for the refeeding days and the time after.
Heart and circulationSauna and the heart
What heat can do to blood vessels and blood pressure.
Sources
All studies were checked via PubMed, cross-checked with Consensus and linked with their DOI. The study type is given in square brackets so that you can judge the strength of the evidence yourself.
- Wilhelmi de Toledo F, Buchinger A, Burggrabe H, Hölz G, Kuhn C, Lischka E, Lischka N, Lützner H, May W, Ritzmann-Widderich M, Stange R, Wessel A, Boschmann M, Peper E, Michalsen A. Fasting therapy: an expert panel update of the 2002 consensus guidelines. Forsch Komplementmed. 2013;20(6):434-43. DOI: 10.1159/000357602 [Consensus Guideline, expert guideline of fasting medicine]
- Wilhelmi de Toledo F, Grundler F, Bergouignan A, Drinda S, Michalsen A. Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects. PLoS One. 2019;14(1):e0209353. DOI: 10.1371/journal.pone.0209353 [Cohort study, prospective, n=1422]
- Koppold DA, Breinlinger C, Hanslian E, Kessler C, Cramer H, Khokhar AR, et al. International consensus on fasting terminology. Cell Metab. 2024;36(8):1779-1794.e4. DOI: 10.1016/j.cmet.2024.06.013 [Consensus Guideline, Delphi process, 38 experts]
- Maifeld A, Bartolomaeus H, Löber U, Avery EG, Steckhan N, Markó L, et al. Fasting alters the gut microbiome reducing blood pressure and body weight in metabolic syndrome patients. Nat Commun. 2021;12(1):1970. DOI: 10.1038/s41467-021-22097-0 [RCT, n=71, exploratory endpoints]
- DeFronzo RA, Cooke CR, Andres R, Faloona GR, Davis PJ. The effect of insulin on renal handling of sodium, potassium, calcium, and phosphate in man. J Clin Invest. 1975;55(4):845-55. DOI: 10.1172/JCI107996 [Pathophysiology, clamp study, n=6]
- da Silva JSV, Seres DS, Sabino K, Adams SC, Berdahl GJ, Citty SW, et al. ASPEN consensus recommendations for refeeding syndrome. Nutr Clin Pract. 2020;35(2):178-195. DOI: 10.1002/ncp.10474 [Consensus Guideline, ASPEN]
- Grundler F, Mesnage R, Michalsen A, Wilhelmi de Toledo F. Blood pressure changes in 1610 subjects with and without antihypertensive medication during long-term fasting. J Am Heart Assoc. 2020;9(23):e018649. DOI: 10.1161/JAHA.120.018649 [Cohort study, n=1610]
- Cahill GF. Fuel metabolism in starvation. Annu Rev Nutr. 2006;26:1-22. DOI: 10.1146/annurev.nutr.26.061505.111258 [Review, human physiology]
- Grundler F, Mesnage R, Ruppert PMM, Kouretas D, Wilhelmi de Toledo F. Long-term fasting-induced ketosis in 1610 subjects: metabolic regulation and safety. Nutrients. 2024;16(12):1849. DOI: 10.3390/nu16121849 [Cohort study, n=1610]
- Mesnage R, Holley A, Grundler F, Martinez-Tellez B, Wilhelmi de Toledo F, Croisille P. Long-term fasting-induced parasympathetic and sympathetic autonomic nervous system modulation in a subgroup of the GENESIS study. Int J Obes (Lond). 2025;49(10):2125-2128. DOI: 10.1038/s41366-025-01843-0 [Pathophysiology, exploratory analysis, n=16]
- Li C, Sadraie B, Steckhan N, Kessler C, Stange R, Jeitler M, Michalsen A. Effects of a one-week fasting therapy in patients with type-2 diabetes mellitus and metabolic syndrome: a randomized controlled explorative study. Exp Clin Endocrinol Diabetes. 2017;125(9):618-624. DOI: 10.1055/s-0043-101700 [RCT, pilot study, n=46]
- Kjeldsen-Kragh J, Haugen M, Borchgrevink CF, Laerum E, Eek M, Mowinkel P, Hovi K, Førre O. Controlled trial of fasting and one-year vegetarian diet in rheumatoid arthritis. Lancet. 1991;338(8772):899-902. DOI: 10.1016/0140-6736(91)91770-u [RCT, single-blind, n=53]
- Müller H, de Toledo FW, Resch KL. Fasting followed by vegetarian diet in patients with rheumatoid arthritis: a systematic review. Scand J Rheumatol. 2001;30(1):1-10. DOI: 10.1080/030097401750065256 [Systematic review with meta-analysis, 4 controlled studies]
- Hartmann AM, Dell'Oro M, Spoo M, Fischer JM, Steckhan N, Jeitler M, et al. To eat or not to eat: an exploratory randomized controlled trial on fasting and plant-based diet in rheumatoid arthritis (NutriFast-Study). Front Nutr. 2022;9:1030380. DOI: 10.3389/fnut.2022.1030380 [RCT, exploratory, n=53]
- Ezpeleta M, Cienfuegos S, Lin S, Pavlou V, Gabel K, Varady KA. Efficacy and safety of prolonged water fasting: a narrative review of human trials. Nutr Rev. 2024;82(5):664-675. DOI: 10.1093/nutrit/nuad081 [Review, narrative, human studies]
- Grundler F, Ducarmon QR, Holley A, Knufinke M, Strathmeyer S, Heelemann S, et al. Health benefits of a five-day at-home modified fasting program: a randomised controlled trial. Genome Med. 2026;18(1). DOI: 10.1186/s13073-026-01681-3 [RCT, n=64]
- Kaufhold G, Bartolomaeus TUP, Schütte K, Schütte T, Kamboj S, Löber U, et al. Machine learning identifies microbiome and clinical predictors of sustained weight loss following prolonged fasting. Genome Med. 2026;18(1). DOI: 10.1186/s13073-026-01765-0 [RCT, waitlist control, n=38]
- Stice E, Davis K, Miller NP, Marti CN. Fasting increases risk for onset of binge eating and bulimic pathology: a 5-year prospective study. J Abnorm Psychol. 2008;117(4):941-6. DOI: 10.1037/a0013644 [Cohort study, prospective, n=496, 5 years]
- Mesnage R, Grundler F, Wilhelmi de Toledo F. Revisiting the (anti)inflammatory effects of prolonged fasting: the importance of baseline-dependent responses. Front Nutr. 2025;12:1715341. DOI: 10.3389/fnut.2025.1715341 [Review, opinion article with an analysis of the n=1422 cohort]
- Michalsen A, Li C. Fasting therapy for treating and preventing disease: current state of evidence. Forsch Komplementmed. 2013;20(6):444-53. DOI: 10.1159/000357765 [Review]
- Naëgel A, Viallon M, Ratiney H, Nguyen T, Leporq B, Kennouche D, et al. Impact of long-term fasting on skeletal muscle: structure, energy metabolism and function using 31P/1H MRS and MRI. J Cachexia Sarcopenia Muscle. 2025;16(2):e13773. DOI: 10.1002/jcsm.13773 [Pathophysiology, prospective MRI study, n=32]