Therapeutic fasting methods: comparison

Therapeutic fasting is generally understood as a deliberate, significant restriction of calories for a specific period, carried out for potential health benefits under the supervision of a specialist. In classical European schools, this typically involves 4-21 days of very low calorie intake, a specific daily routine, exercise, treatments, and medical supervision. Unlike religious fasting or spontaneous fasting when feeling unwell, therapeutic programs are positioned as a structured medical or therapeutic spa treatment. [1]

Historically, several schools of therapeutic fasting have been established: the Buchinger system, the Franz Xaver Mayr approach, and various variations of fasting-dietary therapy. These developed primarily in Europe as sanatorium treatments for patients with chronic musculoskeletal and metabolic diseases, hypertension, rheumatic diseases, and intestinal problems. Modern clinics, continuing these traditions, emphasize that this is a medical intervention for carefully selected patients. [2]

Today, several different approaches are considered therapeutic fasting. These include prolonged water fasting using only water, modified regimens with small amounts of vegetable juices and broths, Buchinger's therapeutic fasting with 200-500 kilocalories per day, and various forms of intermittent fasting, where periods of eating and abstinence alternate within a day or week. Essentially, these methods differ in duration, the depth of the energy deficit, and the degree of medical supervision. [3]

It's important to understand that the term "detoxification" has no scientific basis. A healthy body continuously detoxifies metabolic waste products through the liver, kidneys, intestines, and other systems. Modern reviews emphasize that therapeutic fasting does not "cleanse out toxins" in the conventional sense, but rather affects metabolism, hormones, inflammation, and body weight through measurable biological pathways. [4]

Several areas have attracted the greatest attention from researchers. These include excess weight and obesity, hypertension, metabolic syndrome and type 2 diabetes, chronic inflammatory diseases such as rheumatoid arthritis, as well as mental well-being and chronic pain. For these conditions, there is data of varying quality, ranging from observational studies to randomized trials. However, most experts emphasize that fasting can only be a supplement to standard treatment, not a replacement for it. [5]

The purpose of this article is to examine how the body reacts to fasting, what therapeutic fasting techniques are used, where there are proven benefits, what the risks are, and who should avoid such practices. We will also discuss how to gently utilize fasting ideas without going to dangerous extremes or using fasting as a substitute for medical attention for serious symptoms. [6]

Table 1. Therapeutic fasting: what it is and what it is not

What is this	What it is not
A medical or medical-spa procedure with a controlled calorie deficit and specialist supervision. [7]	A universal way to “remove toxins” and “completely cleanse the body” for any person. [8]
A method that may alleviate the course of some chronic diseases in carefully selected patients. [9]	Replacement of drug therapy, surgery or other standard treatments. [10]
A structured calorie reduction option in a clinical setting or under the supervision of a physician. [11]	A trendy “detox marathon” that anyone can do at home without examinations or supervision. [12]
A temporary intervention with a clearly defined timeframe and exit protocol. [13]	A lifestyle of persistent severe nutritional deficiency and chronic malnutrition. [14]

How the body reacts to fasting

In the first 12-24 hours after fasting, the body primarily uses up glycogen stores in the liver and muscles. Along with glycogen, a significant amount of water is lost, so the rapid initial "weight loss" during fasting is primarily water and intestinal contents, not burned fat. During this stage, blood glucose levels in healthy people typically remain within normal limits due to internal reserves. [15]

After 24-72 hours, fat reserves gradually become more actively utilized. The liver begins actively producing ketone bodies, which become an additional source of energy for the brain and other tissues. Clinical studies on prolonged therapeutic fasting describe controlled ketosis, which remains within the adaptive response in healthy individuals. However, if this regulation is disrupted, especially in the presence of diabetes and certain medications, dangerous ketoacidosis may develop. [16]

Studies have described changes in numerous hormones and mediators following therapeutic fasting. Insulin levels and insulin resistance are reduced, sensitivity to leptin and ghrelin is altered, and levels of chronic inflammation markers are reduced. A number of studies have demonstrated a reduction in C-reactive protein and other inflammatory markers, which is considered one mechanism for symptom relief in rheumatoid arthritis and other inflammatory diseases. [17]

At the cellular level, autophagy and stress resistance are discussed. Animal experiments show that periods of fasting can enhance "cellular housekeeping" processes, increase resistance to oxidative stress, and shift metabolism to a more energy-efficient mode. In humans, these effects are partially confirmed indirectly, but direct large-scale studies with rigorous endpoints are still extremely limited, so drawing sweeping conclusions about "rejuvenation" is premature. [18]

Psychological changes are also noted: according to observational studies, some patients experience improved mood, decreased anxiety and chronic pain, and a feeling of "lightness." On the other hand, a significant proportion of people experience weakness, irritability, headaches, insomnia, and decreased performance during fasting. Clinical programs take all of this into account when selecting the duration and depth of fasting, as well as the activity regimen. [19]

It's crucial to distinguish between short-term, moderate calorie deficits and long-term, strict fasting without medical supervision. The former can be relatively safe for a healthy person and akin to a regular calorie reduction, while the latter is considered a medical intervention with the risk of serious complications. This is why scientific data on therapeutic fasting has primarily been obtained in clinical settings, not in home experiments. [20]

Table 2. Conventional scale of the body's reactions to fasting

Time without food in a healthy adult	Main processes	What does a person feel most often?
Until 12 o'clock	Use of glucose from the last meal and glycogen stores, mild energy deficit	Mild hunger, sometimes food is not remembered due to being busy with things
12-24 hours	Active consumption of glycogen, the onset of more pronounced lipolysis, mild ketonemia	Hunger, possible irritability, thoughts about food, sometimes headache [21]
24-72 hours	Increased ketone body production, decreased insulin, changes in hunger and satiety hormones	Weakness or, conversely, a feeling of “lightness”, headaches and insomnia are possible [22]
3-10 days under medical supervision	Stable ketosis, significant calorie deficit, significant weight loss, changes in inflammatory markers	Weight loss, mood changes, sometimes improvement in pain, but also risk of side effects [23]
More than 10 days	Further increase in deficiency, increased risk of complications, especially without medical supervision	High risk of severe weakness, electrolyte disturbances and other complications, requires strict monitoring [24]

Basic methods of therapeutic fasting

Buchinger's classic therapeutic fasting involves a very low calorie diet, consuming vegetable broths, diluted juices, a small amount of honey, and plenty of fluids. Typically, it involves 200-500 kilocalories per day for 4 to 21 days under medical supervision. The program includes physical activity, breathing exercises, psychological support, and a strictly controlled exit with a gradual expansion of the diet. [25]

Water therapeutic fasting involves abstaining from all food except water. Medical centers use it for 3-10 days and sometimes longer, but only after examination and with ongoing monitoring, including monitoring of blood pressure, electrolytes, ketone bodies, and overall well-being. Reports of such programs show reductions in body weight and blood pressure, but emphasize the need for strict patient selection and an experienced team. [26]

Modified therapeutic fasting regimens include very low-calorie diets of 500-800 kilocalories per day, fasting days on kefir, vegetables, rice, and similar options. Strictly speaking, these are not complete fasting, but a form of restricted dieting. However, in terms of their effects on body weight and individual markers, they are similar to short-term therapeutic fasting programs. These are easier to ensure safety, but if you have chronic illnesses, it is also advisable to discuss such regimens with your doctor. [27]

A separate, larger group is intermittent fasting. These are regimens in which periods of eating and abstinence alternate within a day or week: a 16-hour fast and 8-hour fast, a 5-day normal diet and 2 low-calorie days, or a 4-day normal diet and 3 days of significant calorie restriction. Modern, large reviews show that such approaches produce weight loss comparable to traditional calorie restriction and improve a number of metabolic indicators. [28]

An important practical point: prolonged therapeutic fasting, especially water-based fasting, is considered a medical intervention and should be performed in a clinical setting. Intermittent fasting and gentle low-calorie regimens can be used on an outpatient basis, but require individual adjustments for those with diabetes, cardiovascular disease, or other conditions. Experimenting with multi-day fasts at home, without examination and supervision, increases the risk of serious complications and is not considered safe. [29]

Table 3. Basic methods of therapeutic fasting

Methodology	Caloric content	Typical duration	Where permissible
Buchinger's fast	200-500 kilocalories per day from juices, decoctions, and honey	4-21 days	Only specialized clinics under the supervision of a physician [30]
Water fasting	Just water, zero calories	3-10 days or more in individual cases	Medical centers, strict monitoring of the condition [31]
Modified fasting	500-800 kilocalories per day, fasting days	From 1 day to several weeks	Outpatient, but preferably after consultation with a doctor [32]
Intermittent fasting	Variable calorie deficit by day or hour	Months and years as a style of eating	Outpatient, for chronic diseases with the participation of a doctor [33]

Possible benefits of therapeutic fasting

For overweight and obese individuals, therapeutic fasting and intermittent fasting result in weight loss and fat loss. Systematic reviews show that, on average, these regimens are no better than classic continuous calorie restriction, but are also comparable in terms of weight loss. Many patients find intermittent fasting psychologically easier because it doesn't require constant calorie counting, and clinical therapeutic fasting provides a quick start and additional motivation if the person subsequently transitions to a healthier diet. [34]

In studies of metabolic syndrome and type 2 diabetes, intermittent fasting and structured therapeutic fasting have been shown to improve glycemic control, reducing glycated hemoglobin, body weight, waist circumference, blood pressure, and LDL cholesterol levels. Meta-analyses emphasize that such regimens may be considered as a dietary option for some patients, but only under medical supervision and with adjustments to the dosages of hypoglycemic medications. [35]

For inflammatory diseases of the musculoskeletal system, primarily rheumatoid arthritis, there is evidence of reduced pain and morning stiffness, as well as improved functional status, with therapeutic fasting, especially when combined with a plant-based diet. A number of studies, including the Buchinger program, demonstrate a reduction in inflammatory markers and symptoms in some patients. However, fasting does not replace standard antirheumatic therapy, but serves as an adjunctive method. [36]

Some studies have described a reduction in blood pressure and an improvement in the cardiovascular risk profile in people with hypertension and atherosclerosis risk factors. Intermittent therapeutic fasting in hospital settings resulted in significant reductions in blood pressure and body weight, as well as improvements in participants' well-being and quality of life. However, randomized controlled trials for hard endpoints such as heart attack or stroke are virtually nonexistent, so it is premature to speak of a proven reduction in the risk of events. [37]

Interesting data on the effects of therapeutic and intermittent fasting on mood, stress levels, and chronic pain are available. Observational studies and small patient series have reported improved mood, decreased anxiety, reduced pain perception, and improved sleep patterns. It is suggested that this may be due to changes in serotonin levels, endogenous opioids, and endocannabinoids. However, the risk of expectancy effects and the influence of the spa treatment format is particularly high here, so the results require cautious interpretation. [38]

However, there is no convincing evidence that therapeutic fasting in humans prolongs life, prevents cancer, or can radically "rejuvenate" the body. Most of the data on life extension with calorie restriction and intermittent fasting is obtained from animal models. In humans, we can currently only talk about the effect on risk factors, but not about a proven increase in lifespan. [39]

Table 4. Conditions for which therapeutic or intermittent fasting has been studied best

State	What the research showed	Level of evidence
Obesity, excess weight	Weight loss comparable to conventional calorie restriction, improvement in a number of metabolic parameters. [40]	Moderate: There are randomized trials and meta-analyses, but long-term data are limited.
Metabolic syndrome, type 2 diabetes mellitus	Improvement of glycemia, body weight, blood pressure and lipid profile with controlled regimens. [41]	Moderate: There are meta-analyses and randomized trials, longer follow-up is needed.
Rheumatoid arthritis and other inflammatory diseases	Reduction in pain, stiffness and inflammatory markers in some patients with therapeutic fasting, especially when followed by a plant-based diet. [42]	Limited for now: samples are small, design is not always strict.
Arterial hypertension and risk factors for atherosclerosis	Reduction of blood pressure, body weight and some risk markers during long-term therapeutic fasting in the clinic. [43]	Limited: Randomized studies with long-term follow-up are needed.
Life extension, cancer prevention	There is no direct evidence from humans, the data comes mainly from animal experiments. [44]	Low: The hypotheses are interesting, but there is insufficient clinical evidence.

Risks, side effects and contraindications

Even in clinical settings, therapeutic fasting is associated with side effects. In reviews of patient records of water fasting, the most common symptoms were weakness, headaches, dizziness, coldness, sleep disturbances, and muscle pain. Many of these symptoms were mild to moderate, but in some individuals, they required adjustments to the regimen, fluid and electrolyte intake, or early termination of the program. [45]

More serious complications include hyponatremia and other electrolyte imbalances, hypoglycemia, severe hypotension, arrhythmias, exacerbation of gout, and rare cases of ketoacidosis. Cases of fasting ketoacidosis have been described in people without diabetes after religious or excessively prolonged fasting, as well as episodes of diabetic ketoacidosis in patients with diabetes who combined fasting with certain hypoglycemic drugs, especially sodium-glucose cotransporter inhibitors.[46]

Strict contraindications for therapeutic fasting include pregnancy and breastfeeding, age under 18, severe malnutrition, active cancer with cachexia, severe chronic heart, kidney, or liver failure, uncontrolled type 1 diabetes mellitus, and type 2 diabetes on intensive insulin therapy. For patients with eating disorders (anorexia, bulimia, binge eating disorder), fasting can seriously worsen the course of the disease and is strictly not recommended. [47]

Even with relative indications and the absence of obvious contraindications, independent experiments with prolonged fasting at home pose risks. In real-life settings, people often continue taking medications without adjusting dosages, fail to monitor blood pressure and electrolytes, and don't know when to immediately stop the program and consult a doctor. Safety reviews emphasize that most serious complications occur during uncontrolled fasting, not in specialized centers. [48]

A separate issue is the psychological risks. Fasting easily triggers a mechanism of "strict" restrictions and a fixation on weight control and purity of diet. In people with a tendency toward perfectionism and anxiety, this can lead to the development or worsening of eating disorders, depression, and anxiety disorders. Psychological screening and support are considered an important part of therapeutic fasting programs in clinics, but are virtually absent in independent attempts at home. [49]

Finally, a serious problem is the delay in diagnosis and treatment under the guise of "therapeutic fasting." A person with severe fatigue, chest pain, persistent digestive problems, or a suspected serious illness may experiment with fasting for months instead of undergoing an examination. This delays the initiation of necessary therapy and sometimes leads to the disease being diagnosed at an advanced stage. [50]

Table 5. For whom therapeutic fasting is especially dangerous

Patient group	Main risks	Comment
Pregnant and lactating women	Deficiency of energy and nutrients in the mother and fetus, impaired lactation	Therapeutic fasting is not used during these periods. [51]
People with severe cardiac, renal, or hepatic insufficiency	Decompensation, electrolyte disturbances, organ dysfunction	Requires careful dietary therapy, not starvation. [52]
Patients with type 1 diabetes and complex type 2 diabetes	Ketoacidosis, severe hypoglycemia, unstable glycemia	Fasting is possible only in the form of mild restrictions and strictly under the supervision of a physician. [53]
People with eating disorders	Worsening of symptoms, relapse of the disease, increased mortality	Fasting is contraindicated; if you want to lose weight, you need to work with a psychotherapist and a doctor. [54]
Elderly, debilitated patients, cancer patients with cachexia	Rapid loss of muscle mass, worsening prognosis	The main goal should be to improve nutrition, not restrict it. [55]

How to approach the idea of therapeutic fasting safely

If someone is interested in therapeutic fasting, the first step should be a consultation with a doctor who knows their medical history. It's advisable to discuss goals such as weight loss, improved blood pressure or sugar control, or pain relief from an inflammatory condition. The doctor will help assess the risks, medications being taken, and the need for blood tests and other examinations before any significant dietary intervention. [56]

In many cases, instead of long-term therapeutic fasting, it's more appropriate to begin with simpler and safer measures. These include gradually reducing calorie intake according to a coordinated plan, changing the diet toward vegetables, whole grains, fish, and vegetable oils, and increasing physical activity based on health status. Systematic reviews show that these approaches are comparable to complex fasting regimens in terms of impact on body weight and risk factors, and sometimes even superior in terms of sustainability. [57]

Moderate intermittent fasting, such as limiting food intake to 8-10 hours per day for a healthy person, can be considered as a dietary option in the absence of contraindications. It is important that the diet remains nutritious during the permitted hours, and that the energy deficit is reasonable, not extreme. If you have diabetes, cardiovascular disease, gout, or severe liver or kidney disease, this regimen should be discussed with a doctor, as a change in treatment may be necessary. [58]

If full-fledged therapeutic fasting is being considered, it's wise to choose programs at experienced clinics with a scientific foundation, rather than "detox tours" of dubious quality. Important signs of a responsible approach include a full medical examination before beginning, clear selection and exclusion criteria, daily medical monitoring, informed consent with a description of the risks, a detailed plan for exiting the fast and long-term dietary changes. Programs that promise a "complete cure for all diseases" and do not require a preliminary examination should be viewed with caution. [59]

For those looking to "reset" their diet without drastic interventions, a short period of a gentle, low-calorie diet can be a reasonable compromise. For example, 3-7 days of abstaining from alcohol, fast food, sweets, and fried foods, with an emphasis on vegetables, moderate grains, fish or poultry, and adequate fluid intake. This approach reduces calories, improves dietary composition, and is generally safe for most healthy people, as long as you don't let yourself become extremely hungry and weak. [60]

It's important to recognize the warning signs that indicate you should immediately stop any fasting experiment. These include severe dizziness, fainting, palpitations, severe weakness, chest pain, shortness of breath, uncontrollable vomiting, intense thirst, confusion, and sharp abdominal pain. If these symptoms appear, seek medical attention as soon as possible rather than waiting for the symptoms to "cleanse the body and go away on their own." [61]

Table 6. Therapeutic fasting, intermittent fasting, and regular calorie restriction: what's the difference?

Approach	Pros	Disadvantages and limitations
Long-term therapeutic fasting in the clinic	Rapid weight loss, pronounced metabolic and anti-inflammatory effects, structured regimen and specialist support. [62]	High cost, need for selection and monitoring, unavailable for many patient groups, risk of complications even with monitoring. [63]
Moderate intermittent fasting	Weight loss comparable to a permanent deficit may be easier for some people to maintain and may improve metabolic parameters. [64]	Not suitable for some patients with chronic diseases; if used incorrectly, overeating and breakdowns are possible. [65]
Classic continuous calorie reduction and dietary changes	Well studied, accessible to most, easily adaptable, compatible with the treatment of various diseases. [66]	It requires discipline and support, the effect is less “fast and spectacular”, which reduces motivation in some people.

Frequently asked questions about therapeutic fasting

Is it possible to cure a serious illness with the help of therapeutic fasting without pills and surgery?

To date, there is no evidence that therapeutic fasting alone can cure cancer, cardiovascular disease, autoimmune disease, or other serious illnesses. The best results have been observed when fasting is used as a complement to standard therapy, not as a replacement for it. When fasting is used as a substitute for necessary medications or surgeries, the prognosis typically worsens. [67]

Is it safe for a healthy person to fast periodically for preventative purposes?

In relatively healthy adults, moderate forms of intermittent fasting and short periods of moderate calorie restriction are usually well tolerated, as long as the diet is otherwise balanced and there are no underlying medical conditions. However, even in this group, headaches, weakness, irritability, and decreased performance are possible. If any alarming symptoms appear or any chronic illnesses are present, it is advisable to first discuss any regimen with a doctor. [68]

How does therapeutic fasting differ from popular “detox diets”?

In the medical sense, therapeutic fasting has clear protocols, patient selection criteria, a monitoring regimen, and scientific data on safety and effects. "Detox diets," by contrast, are often advertised as a one-size-fits-all "cleansing" method, lacking the support of serious research and often combining dietary restrictions with unproven supplements and harsh laxatives. This is why doctors emphasize that if therapeutic fasting is to be considered, it should only be within the framework of medical programs, not just another internet challenge. [69]

How many days can you fast at home without harm?

There is no reliable, universal answer, because the risk of complications depends on the initial condition, body weight, the presence of chronic diseases, and medications taken. Even a three-day water fast in a person with undiagnosed diabetes or heart disease can result in serious problems. Current recommendations suggest that any fast longer than 24 hours with a noticeable deterioration in health requires consultation with a specialist, and long-term courses should only be undertaken under medical supervision. [70]

Does it make sense to have a “fasting day” once a week?

For some healthy people, a fasting day, which involves moderate calorie reduction and avoiding overeating, can be a psychologically comfortable way to control their diet. However, its effect on health is largely determined by the overall weekly dietary structure. If a person eats modestly for one day and overeats for the other six, there will be no benefit. However, if a fasting day is integrated into an overall healthy regimen, it can help maintain weight and avoid strict dieting. [71]

Table 7. Therapeutic fasting: myths and facts

Myth	Fact
"Fasting completely cleanses the body of toxins."	The body is constantly neutralizing metabolic products; therapeutic fasting affects metabolism, but does not “wash” the blood and organs. [72]
"Long-term fasting can be done safely at home"	Serious studies on long-term fasting are conducted in monitored clinics; at home, the risk of complications is much higher. [73]
"Intermittent fasting is always better than a regular diet."	On average, the effect on weight loss is comparable; the specific choice of regimen depends on the person and their illnesses. [74]
"Therapeutic fasting prolongs life and prevents cancer"	There is no such evidence for people; we can only talk about the influence on risk factors. [75]
"Fasting is suitable for everyone"	There are wide groups of patients for whom fasting is contraindicated or extremely risky. [76]

Ultimately, therapeutic fasting should not be viewed as a universal cure-all, but rather as a potentially useful, yet risky, tool that is only appropriate in specific situations, with a clear understanding of goals and contraindications, and under the supervision of specialists. For most people, it is more reliable and safer to prioritize sustainable dietary and lifestyle changes rather than extreme experiments with complete abstinence from food. [77]