Three fasting approaches promise success in losing weight. What are the differences, which method is right for you and what should you keep in mind?
Anyone who wants to fast today is spoiled for choice: 16:8, 5:2, “One Meal a Day”, mock fasting, therapeutic fasting according to Buchinger – the list of methods seems endless. But behind the diversity there are essentially three fundamentally different approaches: time-limited interval fasting, calorie-reduced false fasting and radical classic fasting. Lent from Ash Wednesday to Easter offers the perfect opportunity to, with the help of neurophysiologist Dr. Gerd Wirtz to find out which type suits whom. Our free fasting diary offers you orientation and structure.
Intermittent fasting offers gentle habituation instead of radical changes
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The 16:8 intermittent fasting – fasting for 16 hours, eating for 8 hours – is considered the ideal way for those who want to fast. “Intermittent fasting is trendy because it’s easy to do. You only go without food for a certain period of time, but you don’t necessarily have to reduce your calories overall during the day,” explains Wirtz in an interview. The method can be easily integrated into everyday life: Anyone who skips breakfast and only eats lunch has already won.
But be careful about starting things that are too radical. “16:8 is no longer viewed as strictly because young women in particular of childbearing age have slightly different energy requirements and for them 16 hours of fasting could be too long,” warns the neurophysiologist. His recommendation: You automatically fast for 7 to 8 hours at night. Instead of normally eating breakfast immediately after getting up, you should wait half an hour and extend this period every one to three days.
Intermittent fasting basically scores points when it comes to cardiovascular effects. According to a study (2025), blood pressure, cholesterol levels and blood sugar measurably improve. The reason is the regular meal breaks, which give the metabolism time to regenerate. However, anyone hoping for dramatic body changes in a very short time will be disappointed. A meta-analysis in the British Medical Journal (2025) shows that weight losses are no greater than with traditional diets.
Fasting diary – free PDF
Your companion through Lent: Here you can download the fasting diary as a PDF for freesave or print. Includes fasting calendar and habit tracker for reflection and motivation.
Mock fasting as a compromise between renunciation and enjoyment
The so-called false fasting or the “Fasting Mimicking Diet” (FMD) seems much more radical. “In mock fasting, there is a so-called adjustment day with 700 to 800 calories, then only 400 to 500 calories a day,” says Wirtz, explaining the method of the Italian aging researcher Valter Longo. This phase usually lasts five days.
The secret lies in the composition of the food: “You eat very little protein, take long breaks and practically completely avoid simple carbohydrates. This keeps the insulin level constantly low.” Mock fasting can be interesting for those who want to reap the benefits of fasting without completely abstaining from food.
According to an analysis (2024), the biological age should decrease by 2.5 years after three cycles. However, caution is advised: Valter Longo is co-founder of the company L-Nutra, which markets ready-made mock fasting packages under the name ProLon. This conflict of interest should be taken into account when evaluating the study results.
To person
Dr. Gerd Wirtz is a neurophysiologist, medical presenter, bestselling author and keynote speaker. He is considered one of the leading experts in digital health and longevity. In seminars and coaching, he teaches scientifically based strategies to maintain health, extend lifespan and increase quality of life. His current book “The Longevity Compass” offers practical tips for a long, healthy life.
Therapeutic fasting shows the most radical effects
Traditional water fasting or therapeutic fasting according to Buchinger shows the clearest effects on weight loss. Fasting people abstain from solid food for seven to 21 days and only consume water and tea as well as minimal calories in the form of vegetable broth and finely pureed vegetable or cream soups (without cream).
“With therapeutic fasting, the calorie reduction is a little greater,” says Wirtz, describing the method. The difference to false fasting is psychologically crucial: “With therapeutic fasting, the emotional stress is a little greater because you really don’t eat any solid food.”
Download the free PDF “Fasting Diary” with fasting calendar and habit tracker HERE.
However, it is only after three days that the major changes in the liver, kidneys and other organs begin. Blood sugar and insulin drop sharply in the first three days of fasting. But fat burning and ketone body formation peak only after 17 days. A review from 2024 confirms these hormonal cascades and shows that fasting influences a whole range of metabolic hormones.
But therapeutic fasting also has its downsides: inflammation levels in the blood increase – a warning signal that researchers do not yet fully understand. A large overview study (2025) shows that prolonged fasting often increases inflammatory markers. In addition, the kidneys work worse. A study (2018) involving 11 days of water fasting showed increased uric acid and creatinine levels. Renal function was impaired but remained within normal limits and fully recovered after fasting.
According to Buchinger, coffee is generally taboo during traditional therapeutic fasting. It is considered a luxury food and can hinder detoxification. There are exceptions in the case of severe withdrawal symptoms or as a gradual renunciation: then black coffee is permitted in small portions.
