How healthy is fasting?


Fasting triggers various processes in the body after just 12 hours, which according to research, benefit our health. Although additional long-term studies are needed to prove the results conclusively, current research looks promising.

What happens in the body during fasting

First 12 hours

The first few hours of fasting see normal processes taking place in the body. The body breaks down glycogen, a glucose polysaccharide, from the liver and muscles to produce energy.

After 12– 24 hours

After 12–24 hours, after the glycogen stores are exhausted, the body's metabolism switches to fat as an energy source, a process better known as ketogenesis. During this phase, side effects such as headaches, dizziness, fatigue or muscle pain may be felt.

After 24 hours

Once these resources are also used up, the body goes from fasting into starvation mode. From then on, the body shuts down its metabolism and uses muscle tissue for energy. However, this only takes place after several consistent days of fasting.

Why fasting is healthy

Research – mostly from animal studies – shows that intermittent fasting creates physical benefits. This is because fasting impacts metabolic and cellular processes. The changes in these processes not only improve health factors such as insulin sensitivity, but also reduce blood pressure and have an anti-inflammatory effect.

Autophagy and apoptosis

Fasting is also often linked with autophagy and apoptosis. Autophagy means that cells break down and utilise their own components. Apoptosis goes one step further and leads to a form of programmed cell death, an active process that forms part of our metabolism.

In other words, these two processes help the body to cleanse itself of damaged cells and, for this reason, are also used as a form of therapy. In addition, they prevent diseases such as diabetes, Alzheimer’s and cardiovascular diseases.


Consequently, there is nothing to be said against fasting for a few days, be it for reasons of self-discovery or as a kick-start to weight loss. Sound scientific results on humans – healthy and unhealthy – are yet to be established and require further research. Prolonged fasting, on the other hand, is clearly unhealthy. Anyone choosing any form of fasting should be healthy, drink enough fluids during the fast and, under no circumstances, be pregnant or breastfeeding.

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