Fasting Trends: Charité Expert Explains What Works

• In the video above: Fasting puts the body into a “better aging program” – if you avoid a mistake

Fasting is based on an ancient concept: For centuries, people have consciously abstained from eating at times – for religious, health or therapeutic reasons. Fasting is still in vogue today. One DAK Study from 2025 shows how great the interest is: 72 percent of Germans think fasting makes sense, and among 18 to 29 year olds the figure is even 84 percent.

Fasting expert Andreas Michalsen explains in an interview with FOCUS online which form of fasting is particularly useful in his opinion and classifies the study situation.

1. Mock fasting – particularly recommended

Andreas Michalsen sees mock fasting together with therapeutic fasting as a particularly suitable form of fasting. From a medical point of view, it is considered one of the most effective methods and at the same time most suitable for everyday use – with good studies.

“Today we assume that around 80 to 90 percent of the acute effects of the classic therapeutic fasting according to Buchinger can be achieved,” he explains. More on this in point number two.

This is how mock fasting works

Using a highly calorie-reduced, plant-based diet over five days, the mock fasting method puts the body into fasting mode without completely interrupting the energy supply.

The daily calorie intake is 750 kilocalories on the first day, then around 650 per day.

Basic rules for mock fasting

• Prefers low-starch vegetables and low-sugar, easily digestible fruit.
• Avoid simple carbohydrates such as bread or pasta; small amounts of whole grains are allowed.
• Avoid animal proteins such as meat or dairy products.
• Nuts and high-quality oils provide healthy fats and ensure satiety.

That’s what science says

If the body has significantly less energy available for several days, it changes its metabolism. After about two to three days, the carbohydrate stores are largely used up – then the organism increasingly uses fat reserves and forms so-called ketone bodies, which serve as an alternative energy source for the brain and muscles.

A current study from the specialist magazine shows how powerful false fasting can be “Nature Communications”. After several fasting cycles, participants showed lower insulin resistance, lower risk factors for diabetes and cardiovascular disease, and less liver and body fat. Particularly exciting: The biological age improved by an average of around 2.5 years – regardless of weight loss.

2. Therapeutic fasting according to Buchinger – useful under medical supervision and not as a quick weight loss cure

According to Buchinger, therapeutic fasting is one of the most effective forms of fasting for the fasting expert. Although the study situation is predominantly observational, the results are meaningful. For him, therapeutic fasting is a sensible medical measure, but ideally with medical supervision and not as a quick weight loss cure. This means that therapeutic fasting is not necessarily suitable for everyday life.

This is how therapeutic fasting works according to Buchinger

Therapeutic fasting means abstaining from solid food for a limited time in order to relieve the strain on the body and metabolism. The focus should not be on weight loss, but on regeneration and inner peace.

Buchinger therapeutic fasting goes back to the doctor Otto Buchinger. Drink liquids such as water, unsweetened tea or vegetable broth instead of solid food. Ideally, the treatment is accompanied by a doctor.

Typical process

In preparation, calories are reduced and alcohol, nicotine and caffeine are avoided. On the first day of fasting, the intestines are cleansed with Glauber’s salt.

On the fasting days themselves, a maximum of 250 to 500 kilocalories are consumed daily, for example:

• 250 milliliters of vegetable broth
• 250 milliliters of fruit or vegetable juice
• 30 grams of honey
• at least 2.5 liters of water or herbal tea per day

The Medical Association for Therapeutic Fasting and Nutrition (ÄGHE) recommends seven to ten days of fasting, plus a preparation day and three days of restorative food after fasting.

That’s what science says

A large observational study on Buchinger therapeutic fasting from 2019 shows that fasting noticeably reprograms the metabolism: the body switches its energy supply from sugar to fat reserves and ketone bodies. As a result, the participants lost weight and cholesterol and blood lipid levels improved. In addition, blood pressure and important diabetes markers such as blood sugar fell. Evidence suggests fasting may support cardiovascular health.

At the same time, completely abstaining from food also means stress for the body: in order to save energy, it reduces the basal metabolic rate and can also break down some protein from the muscles. Without accompanying exercise, there is a risk of muscle loss during prolonged fasting.

Nutritionist Andreas Michalsen explains it like this: “Theoretically, some protein is used at the beginning, but high-quality studies with MRI and muscle tests show: The muscle becomes smaller due to water loss, not through real breakdown. After fasting, this returns to normal. In addition, even better muscle function was shown after fasting – probably due to autophagy (Note d. Red. a self-cleaning process of the cells) in the muscle.”

The German Society for Nutrition emphasizes that therapeutic fasting is only suitable to a limited extent for long-term weight loss. However, it can serve as a possible starting point to initiate a conscious change in diet.

3. Intermittent fasting – well researched and safe, but with little effect on health and weight

Andreas Michalsen rates intermittent fasting as well-studied and fundamentally safe, but the effects on weight loss and metabolism are rather limited. Nevertheless, it can help prevent illness in the long term and is a suitable everyday introduction to a healthier diet.

This is how intermittent fasting works

Intermittent fasting, also known as “intermittent fasting”, is a form of nutrition in which fasting is carried out regularly for days or hours, i.e. in intervals.

You only eat within an eight-hour window every day. The remaining 16 hours are fasted. A large part of it falls at night, so that many periods of fasting are “overslept”. This form of fasting is particularly suitable for everyday use.

This involves fasting on two days per week. On fasting days, you may only consume around 20 to 25 percent of your normal calorie requirements. The remaining five days you eat normally, without any special instructions. A fixed rhythm makes implementation easier.

3:4-Methode (Alternate Day Fasting)

This is the strictest variant. Fasting occurs every other day of the week. On fasting days, the calorie intake is also a maximum of 20 to 25 percent of the daily requirement.

That’s what science says

A large analysis of 99 studies showsthat intermittent fasting, like classic diets, can help you lose weight and improve important cardiac and metabolic values. The differences between the individual forms of fasting are usually small. Only alternating fasting according to the 3:4 principle (Alternate Day Fasting) performed slightly better in the short term.

Other scientific studies on mice have shown that the animals that only eat within a certain time window stay slim and live longer than their counterparts who had access to food around the clock and with the same number of calories.

“There are now several large meta-analyses of intermittent fasting. They all come to the same conclusion that after three, six and twelve months there is a slight weight loss of around three to five percent of body weight. Compared to medications that can reach twelve percent or more, this is of course less – but it is safe and well tolerated. You can also see slight improvements in elevated blood pressure and better blood sugar levels in diabetics,” summarizes Michalsen.

Nutritional studies as an indication

Nutritional studies provide valuable information but are rarely considered definitive evidence because many factors such as lifestyle and individual differences influence results.

“After all, you can’t let people fast without them knowing that they’re fasting,” says Andreas Michalsen.

• Pregnant and breastfeeding women
• children and young people
• People who have or have had an eating disorder
• underweight people
• People with serious chronic diseases (heart, kidney, liver, cancer)
• elderly or physically weak people
• People who need important medication on a regular basis
• People with circulatory problems or low blood pressure
• People with gallstones or acute gout symptoms

If in doubt, always seek medical advice first.

Autophagy – the recycling program of cells

When fasting, the focus is often on autophagy – the body’s own recycling program. Damaged or old cell components are broken down and recycled. A process that can support health and strengthen the immune system.

Autophagy is activated primarily when calorie intake is significantly reduced, which is the case when fasting. The metabolism changes, switches to economy mode and uses its energy stores: glycogen, fat and protein. In this way, the body ensures that it continues to function despite the lack – and at the same time “cleanses” the cells.

Fasting expert Andreas Michalsen classifies the process: “Autophagy is an important mechanism, but not the only one. In longevity research, there are 14 hallmarks of aging. Fasting affects many of these mechanisms at the same time. It’s a beautiful picture: the cells ‘clean’ themselves. But fasting also affects insulin, inflammatory processes, repair mechanisms, new stem cell formation and much more.”