Fasting is one of the biggest dietary trends of recent years and is promoted for its weight loss and health benefits. There are different types of fasting, such as abstaining from certain foods, eating within a specific time window, reducing calorie intake, or even completely eliminating solid food for a certain period. Some cultures and religions have practiced fasting for millennia as a way to purify body and mind. Furthermore, our bodies are adapted to periods of fasting, as even Western humans haven’t always lived in abundance and had constant access to food.
What happens in our body when we fast?
A press release from the BIH states: „During extended periods of fasting, our body gradually switches its energy metabolism from sugar and other nutrients from food to its own reserves, primarily fat.“ Therefore, if we don’t eat for a few hours before going to bed and for a few hours in the morning after waking up, and only consume calorie-free drinks like water, unsweetened coffee, and tea during this time, it’s possible to achieve a fasting period of approximately 14 hours. „A food break of at least 14 hours triggers a kind of cleaning process in our cells called autophagy. In this process, damaged cell parts are covered by a membrane and digested. This recycling program makes aged cells fully functional again and could even slow down the aging process ,“ according to a report by NDR . Furthermore, the processes of cell cleaning are also part of an effective immune defense , as emphasized in another report by ARD .
Why fast?
Before we delve into the different types of fasting and eating patterns, it’s important to mention that the term “ fasting “ can also encompass the temporary abstinence from things like sweets, media, alcohol, and meat. Despite the abstinence, which may be temporarily perceived as unpleasant, it has a positive impact on our mental health and mood, because, as the article from the University Outpatient Clinic in Witten states , „Abstinence has a beneficial effect on body and mind, can actually be a spiritual experience, and contributes to increasing our self-efficacy. „
Why not fast?
The NDR report emphasizes that anyone with pre-existing conditions and ailments such as low blood pressure, metabolic disorders, or chronic illnesses should absolutely consult a medical professional before attempting any fasting method. Intermittent fasting is unsuitable during pregnancy and breastfeeding, as well as for individuals with eating disorders and migraines. According to nutritional medicine expert Professor Hans Hauner, those seeking sustainable weight loss should primarily focus on adjusting their diet and increasing their intake of fiber and unsaturated fatty acids.
Types of Fasting
Intermittent fasting:
Intermittent fasting, also known as interval fasting, is a type of short-term fasting because the fasting period is limited to a few hours and is followed by a shorter eating window or a day on which only a fraction of the usual amount of energy is consumed. The NDR article “ Intermittent Fasting: How Healthy Weight Loss Works “ explains the three most common variations as follows:
- The 16:8 method: 16 hours have passed between the last meal of the previous day and the first meal of the current day without any energy intake in the form of food. Two meals can now be consumed within an eight-hour period.
- The 5:2 method: For five days a week, you eat normally, and on the remaining two days, your usual calorie intake is reduced to about a quarter. In her work on this topic, certified nutritionist and PhD in natural sciences Gunda Backes adds that the two fasting days should follow a fixed schedule, for example, Mondays and Thursdays.
- 1:1 method (alternating fasting): On one day you eat normally, and on the following day you consume only about a quarter of your usual calorie intake.
Conclusion: The ARD report “ Different Types of Fasting: Advantages and Disadvantages “ shows that during intermittent fasting, the body lives off its reserves: „In this short period, the metabolism is not slowed down, and muscle mass is not broken down.“ Nevertheless, it is important to understand that no excess energy should be consumed during the eating window or on a day of „normal“ eating. The article “ Nutritional Trend: Fasting: How Healthy is Abstaining from Food? “ clarifies: „The German Nutrition Society does not recommend intermittent fasting as a long-term weight management method, as, for example, concrete recommendations regarding food choices are currently lacking. Furthermore, there are no scientific studies yet on the long-term effects of intermittent fasting.“
Therapeutic fasting according to Buchinger:
This type of fasting is named after the military physician Dr. Otto Buchinger, who suffered from rheumatism and underwent a fasting cure with a colleague at the beginning of the 20th century. He used his own experience, with a focus on health promotion , to develop the therapeutic fasting concept known today.
In the press release “ How healthy is therapeutic fasting? ” from the University Hospital Leipzig, the state-certified dietician Lars Selig appears as an expert and explains that therapeutic fasting according to Buchinger is so effective because this concept is based on a structure: “There is a preparation phase, a kind of intervention phase and a final phase.”
- Preparation phase: For 1-3 days, food intake is reduced and alcohol and caffeine are excluded.
- Intervention phase: A bowel cleanse (e.g., with Glauber’s salt) marks the beginning of the therapeutic fast. On fasting days (duration determined after consultation with medical professionals), food intake is limited to water, vegetable broth, herbal tea, and freshly squeezed fruit and vegetable juices.
- Final phase: For 1-3 days, food intake is increased, starting with vegetable soups and gradually transitioning to more solid food such as steamed vegetables.
In conclusion, the article from the Witten University Outpatient Clinic succinctly states that while therapeutic fasting does lead to weight loss, it is not a suitable method for sustainable weight reduction. However, a therapeutic fast can certainly serve as a starting point for a balanced diet. Lars Selig also emphasizes: „We actually recommend that everyone who wants to fast should have a medical examination beforehand and find someone to support them. This could be a doctor or a specially trained fasting coach.“
Summary
Gunda Backes, a certified nutritionist and PhD in natural sciences, concludes: „The data available so far suggest that intermittent fasting can have a positive effect on health and weight loss, particularly on the reduction of lean body mass […].“ However, long-term data and recommendations for food choices are lacking. Since therapeutic fasting involves several days and sometimes even weeks without solid food, supervision by trained professionals is essential. No other type of fasting has yet been recognized as more effective than a balanced diet and an active lifestyle. Whether you want to try a new diet or take on a challenge for a certain period, remember that your most reliable signals regarding food and fasting are still your natural hunger and satiety cues.
Sources
Berlin Institute of Health (2024): New study shows systematic changes in the body through fasting. Bihealth.org, online at https://www.bihealth.org/de/aktuell/neue-studie-zeigt-systematische-veraenderungen-des-koerpers-durch-fasten
Backes, Gunda: Intermittent Fasting. Dge.de, online at https://www.dge.de/gesunde-ernaehrung/diaeten-und-fasten/intervallfasten/#c2276
German Heart Foundation: Nutrition trend fasting: How healthy is abstaining from food? Herzstiftung.de, online at https://herzstiftung.de/ihre-herzgesundheit/gesund-bleiben/ernaehrung/fasten
NDR (2025): Intermittent fasting: How healthy weight loss works. NDR.de, online at https://www.ndr.de/ratgeber/gesundheit/Intervallfasten-So-funktioniert-gesundes-Abnehmen,fasten224.html
ARD Gesund (2025): Different types of fasting: advantages and disadvantages. NDR.de, online at https://www.ndr.de/ratgeber/gesundheit/Verschiedene-Fastenarten-Vor-und-Nachteile,fasten262.html
University Outpatient Clinic Witten (2024): Healthy Fasting: Is There a Master Plan? Uniambulnaz-Witten.de, online at https://www.uniambulanz-witten.de/gesundes-fasten-gibt-es-den-masterplan/
Leipzig University Hospital (2024): How healthy is therapeutic fasting? Uniklinikum-Leipzig.de, online at https://www.uniklinikum-leipzig.de/presse/Seiten/Pressemitteilung_7848.aspx
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