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Intermittent fasting (IF)

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Intermittent fasting (IF)

Table of contents

Intermittent fasting - what is it anyway?

Intermittent fasting (IF), also known as intermittent fasting, is a variant of fasting that involves stopping drinking and eating at a defined rhythm (hourly or daily). The effects of intermittent fasting include weight loss and metabolic regulation through effects on biorhythms, the gut microbiome and lifestyle (e.g. sleep). In contrast to many other forms of diet or pure calorie restriction, intermittent fasting is much easier to adhere to.

How it works

There are various forms of IF that can be used. The two best-known methods are

5:2 method
This method involves eating normally five days a week without a calorie restriction. On the remaining two days, the calorie intake is then restricted completely or to approx. 500 kcal. It is important to ensure that the two fasting days are not consecutive.
In human studies, it has been observed that this fasting method leads to a significant decrease in weight, fasting insulin levels and fasting glucose levels. Furthermore, some study participants reported a reduction in tension, anger and fatigue as well as an increase in self-confidence and mood. Studies show that it is generally much easier to adhere to fasting on alternate days than to everyday calorie restrictions.

If you limit your calorie intake to around 500 kcal on fasting days instead of completely abstaining from food, there are a few helpful tips to bear in mind:

  • Eating a large meal late in the day is easiest for most people. You may, and this is even healthier, prefer to eat early or spread your food intake over 2 meals. Try out what works best for you.
  • During these days, the focus should be on low-calorie vegetables, protein-rich foods and good fats, e.g. in the form of soups, in order to feel full. Good examples are: grilled salmon, other fish or chicken with vegetables, eggs with prawns, vegetables and olive oil, mixed salad with olive oil, avocado and salmon, chicken and vegetable soup, spinach, onions with salmon, vegetables with cashew nuts, tomato soup with prawns.

16:8 method
In this most widespread form of IF, food intake takes place in an 8-hour phase, followed by a 16-hour fasting period. The positive effects of the fasting period are already noticeable after 12-14 hours. The optimum period is 14-16 hours (max. 18 hours) without food. The charm of this method lies in its simplicity. Due to the sleeping time, during which no food is eaten anyway, most people not only find it much easier than expected to fast for 13-16 hours a day, but it also quickly becomes an integral part of their lives - especially because the many positive effects are quickly noticeable for most people.

How does it work?

  • It is best to eat your last meal early in the evening - before 8 pm in summer and before 5 to 6 pm in winter - and then not eat for 16 hours. IF also shows positive effects if you eat later in the evening. The important thing is to maintain an interval of 13 to 16 hours before the next meal.
  • During the fasting period, calorie-free drinks can be consumed, such as water, unsweetened coffee, herbs or green tea.

That was all you needed to know to get started.

Special tips:

  • Eat no more than two to three times during the eight hours and make sure you eat good food. This includes avoiding soft drinks/fruit juices, sweets, ready meals, bread and red meat on the one hand, and plenty of varied vegetables, mushrooms, fruit, good fats (such as olive oil, oily fish, avocado, nuts) and good proteins (e.g. eggs, chicken, fish and nuts etc.) on the other.
  • Ideally, you should exercise two to three times a week on an empty stomach, e.g. interval training or light endurance training. This further improves the absorption of sugar into the mitochondria - our power stations - and the production of ATP, the main energy store in our cells.

Is intermittent fasting safe?

Most, if not all, studies suggest that intermittent fasting is safe and well tolerated and can result in weight loss of 3-8% in adults who are overweight or obese, even as a permanent lifestyle form. Diabetics should only carry out intermittent fasting under medical supervision. If you have problems with your pancreas, thyroid or adrenal glands, e.g. if you are very overweight, you should start with a low-carb diet or only in consultation with your doctor. Otherwise, it is suitable for people who want to support their health or lose weight.

Impacts and effects

Weight reduction

Severe overweight and obesity in particular are a global health problem due to the risk factors they create, including cardiovascular disease and type 2 diabetes. To prevent the onset and progression of these secondary diseases, weight reduction has become a key strategy. Even several recent systematic reviews have shown that intermittent fasting leads to significant weight loss.

Metabolic regulation

Intermittent fasting also has a positive effect on a variety of markers and risk factors, such as cardiovascular disease, cardiomyopathy, inflammatory parameters, metabolic diseases, cancer, retinal damage (retinopathy), neuroplasticity, cognition and lifespan. Intermittent fasting appears to achieve more positive metabolic effects than pure calorie restriction.


Important parameters for the inflammatory status are homocysteine, interleukin 6 (IL6) and reactive C protein (CRP). Among many others, a recent study from 2019 also showed that intermittent fasting leads to a reduction in the above-mentioned parameters. One factor in excess inflammation in the body is eating too much and too often. Therefore, it is not surprising that intermittent fasting and calorie reduction are actually essential measures to reduce low-grade systemic inflammation, which is considered to be the main cause of many chronic diseases. Thus, by reducing inflammatory and autoimmune processes in the body, diseases such as cardiovascular disease, type 2 diabetes, cancer, fatty liver, type 2 diabetes and obesity, multiple sclerosis, asthma and psoriasis. In addition, calorie reduction and IF slow down the ageing process and prolong life. A 2019 study was also able to clarify more precisely how IF can reduce inflammation in the body, namely by reducing the number of circulating monocytes - these are scavenger cells or precursors of scavenger cells in the blood - as well as their metabolic and inflammatory activity. Fasting improves inflammatory diseases without impairing antimicrobial immunity. Both IF and alternate-day fasting are effective, as is limiting calorie intake to reduce insulin resistance. Insulin resistance is a major mechanism for low-grade inflammation in the body and leads to diabetes in the long term, among other things. Try out which type of fasting is easier for you. For me, 16/8 works the easiest.

Oxidative stress, mitochondria and longevity

A 2017 Harvard study found that fasting can influence the mitochondria, the powerhouses of the cell, to keep them in a "youthful" state, leading to better health and longevity.
Oxidative stress refers to an imbalance between oxidative and antioxidative processes and leads to damage to cell membranes, proteins and enzymes. It favours ageing processes and damage to genetic material. Studies have shown that IF reduces oxidative stress and has an antioxidant effect.

Fat composition

Intermittent fasting leads to a significant improvement in total cholesterol, low-density lipoprotein cholesterol (LDL) and triglycerides. These are the unhealthy fats in the body that favour the development of cardiovascular disease and inflammation of the pancreas. It is therefore very good that IF reduces these fat levels. In animal experiments, fasting days not only showed an improved blood sugar and fat value profile, but also more efficient mitochondrial respiration in the skeletal muscles. Fat burning is promoted by IF.

Circadian rhythm

Circadian rhythm is the ability to synchronise physiological processes to a period length of around 24 hours. A desynchronisation of the peripheral circadian clocks in liver, fat and muscle cells, e.g. triggered by eating at night, can increase the risk of certain chronic diseases such as diseases of the cardiovascular system and/or metabolism and cancer. Intermittent fasting, on the other hand, promotes optimal synchronisation of the hormonal response.


Initial animal models suggest that IF has positive effects on intestinal microbiotics, as our intestines are also subject to circadian rhythms. These can be better synchronised by limiting food intake to a few hours a day. Intermittent fasting can also have a direct effect on the microbiome by contributing to the diversity of the gut microflora.


Intermittent fasting improves memory and cognition in animal studies.

Health behaviour and sleep

Intermittent fasting has the potential to influence people's health behaviour. Numerous observational studies have shown that eating at night is associated with reduced sleep duration and poor sleep quality, which can lead to insulin resistance and an increased risk of obesity, diabetes, cardiovascular disease and cancer. One study found that fasting for more than 14 hours at night led to significant weight loss as well as improvements in sleep satisfaction, satiety at bedtime and energy levels.


Studies on IF suggest that it can prolong life and have a positive impact on health in general and on diseases of the cardiovascular system and/or metabolic processes in particular. However, further large-scale studies with long-term data and scientifically proven recommendations for food selection within the periods of food intake are required.
Based on the results so far, however, it seems to be worth trying out intermittent fasting and observing the changes it leads to in yourself. Especially in combination with other healthy lifestyles such as more exercise and regular breaks from sitting (see article: Sitting break), the effect of IF can be even stronger. It also makes sense to combine intermittent fasting with a diet of high-quality healthy foods (see above).

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