Intermittent fasting – a term that is slowly but surely established in our society. Longer fasting, for example in a therapeutic fasting cure, was known earlier, but the trend of interval fasting has only come to us in recent years. It is basically a matter of regularly incorporating smaller phases of fasting into everyday life. This should have positive effects on health, performance and concentration, as well as helping to lose weight. However, what the physiological justification is related to the metabolism is rarely found in the descriptions. This will now be examined in more detail here, in order to refute or possibly also question the positive effects advertised.
What are the benefits of intermittent fasting?
Part-time fasting in various variations, which are explained in more detail below, is said to have many advantages:
The intestinal health is optimized by the resting phases, chronic inflammations are reduced and the body detoxifies many harmful substances during this time. The liver and kidneys can focus on binding and excreting toxins and are not simultaneously burdened with substances from food intake. The regeneration and renewal of cells also takes place during intermittent fasting. One speaks of a self-healing process of the body. It is also said to even rejuvenate the cells and help them lose weight.
What does intermittent fasting mean? > Definition <
Compared to therapeutic fasting or fasting on bases, interval fasting is something that is built into everyday life as a fixed, long-term routine. It usually involves 12 to 24 hours during which no calories are consumed. There are however smaller exceptions, which are dealt with in more detail in the various methods. By definition, intermittent fasting is primarily about when to eat and not what1. Here however from this philosophy one advises against, because if one combines a healthy nourishing way with chamfered, the effect might be the more strongly. And even if chamfered probably has many health advantages, the body needs nevertheless the correct macro nutrients and micro nutrients, in order to be able to function.
The partly already other names mentioned such as short-term fasting, interval fasting, partial fasting and part-time fasting all mean the same generic term for the different methods.
Instructions for interval fasting - when should you fast? For whom is fasting suitable?
According to a hypothesis from the theory of evolution, intermittent fasting lies in our genes, which have not changed much in this respect since primeval times. It is assumed that our body is made for longer periods without food, because at that time there was not a supermarket on every corner and sometimes there was simply no food available2. Therefore, fasting is suitable for almost everyone. However, people who have certain illnesses and take medication should be careful. Even if short-term fasting could even minimize their problems for many of them, you should first talk to their doctor about it. Even diabetics could benefit, as fasting can improve insulin sensitivity, but there are aspects to consider that a doctor should clarify.
Women should generally fast for shorter periods than men, due to hormonal conditions often 12-14 hours are sufficient and more would often be counterproductive, because too many stress hormones can be produced. For men it should rather be at least 16 hours, as the desired processes in their metabolism take effect a little later and their body is more resistant to stress.
Pregnant women should not fast, because they need the regular food supply for the nutrient supply of their child.
With all methods, bedtime is used as a time of fasting, as there is no eating or drinking there anyway. As sleep usually takes 6-8 hours, the time immediately after or before is used to make up the missing time - or both. For example, one has the last meal in the afternoon and the next one in the morning the following day. Or you eat something in the evening and fast until noon the next day.
For how long should the fasting last?
How long one should fast depends on the method. This should be chosen individually and adapted if necessary. Basically, however, the period of fasting depends on gender, general health, stress levels, hormone release and experience. Beginners should start interval fasting rather defensively and get to know their body to find out which method is the right one in the long run. It is best to start with 12-14 hours, starting at 6 or 7 pm the evening before.
How many times a week you perform the fasting phases depends on the method and your personal possibilities and needs. Basically, the shorter the fasting period, the more often one should fast. So it makes sense to fast 12 hours a day for 12/12, other methods already specify that, for example, two full days per week should be fasted.
Weight loss through interval fasting
Especially those who want to lose weight will notice that intermittent fasting is very effective in many cases. A study with mice, for example, proved that the time-restricted feeding mentioned there allowed the animals to stay slim, although they were given the same amount of calories as the control group, who always had to eat. The fasting mice were only fed at night when it was dark and not when it was light during the day. So they fasted for 16 hours a day. The mice that were constantly eating became obese, resistant to satiety hormones, had chronic inflammation and poor liver function and also developed insulin resistance. None of these diseases occurred with the intermittently fasting mice group; on the contrary, they all remained healthy and, above all, slim12.
Unfortunately, there are no such studies on humans at present, as nutritional issues take a very long time and the topic is still too topical for that. However, there are many practical examples and sufficient physiological explanations why interval fasting has such positive effects for us too:
By emptying the digestive tract, hormonal signals are changed. Because the blood sugar level drops without glucose absorption via the intestines, insulin secretion is reduced. Insulin is the hormone that promotes the absorption of sugar into the cells. You can find more about blood sugar here.
The hormones glucagon and adrenaline, which signal the transport of stored sugar into the bloodstream, are released in increased quantities to supply the cells with energy2. In addition, fat reserves are released, which also serve as a source of energy and further processes that draw energy from amino acids begin. After already 12 hours, ketone bodies are also used in addition. These serve as a substitute for sugar, because some body cells cannot use fatty acids as energy carriers8.
Autophagocytosis – an intelligent cell purification
Intermittent fasting promotes autophagocytosis11. This is a form of programmed cell death, in which damaged cells and those affected by pathogens are destroyed and their components are then converted into energy sources and used. It is therefore a kind of recycling process in the body. It is somewhat unclear when this state begins, various sources report the onset of autophagocytosis after 12, 14 and 16 hours10,11. It can probably be assumed that it is again individually dependent, as already described earlier in the text.
Methods – models of interval fasting: 12/12 - 14/10 - 16/8 - 20/4 - 24/0 - 5/2
- 16/8 Intermittent fasting is currently the most popular method. Here, food is abstained from 16 hours ago. As already mentioned, this is usually the minimum fasting period for men in order to achieve the desired effect. It could also be considered for very fit and stress-resistant women.
- 14/10 fasting works on the same principle and is the most recommended method for women. Fasting is followed by 14 hours of fasting, so breakfast is taken late or dinner is taken early.
- 12 hours of interval fasting is a good entry method, which is suitable for almost everyone. As mentioned, this form of short-term fasting is best done daily. Here the effect is actually strongest if the fasting phase begins at least 3-4 hours before sleeping. This is because during this period the release of the sleep hormone melatonin already begins, which activates a gene that reduces insulin secretion5. As a result, blood sugar levels are raised more strongly and for longer periods when eating shortly before sleep, which has a negative effect on sleep quality and hormone secretion as well as weight loss.
- Intermittent fasting of 20 to 24 hours is already very advanced and less relevant for many, as these forms require a stable stress and hormonal system and are not always easy to integrate into everyday life. Even for people who do a lot of sport, the long fasting period can be counterproductive.
- The 5/2 method of fasting is an extended form of the latter method. Here everything is eaten 5 days a week according to your mood and two days a week (whether distributed or consecutive) only 500 to 600 calories are consumed. This can be very efficient in losing weight, but it involves the same problems or risks as the 20/4 and 24/0 method. This can also be called a diet, and these are usually not sustainable.
What is allowed during interval fasting? Coffee, tea and co.
There are different opinions on the subject of coffee and small calorie quantities. With the 5/2 method, a daily calorie amount of 500-600 Kcal is allowed, which is why misunderstandings often arise:
As for the other methods, many people understand that they are allowed to eat, for example, a Bulletproof coffee that contains fat and collagen (protein). This does not make sense, however, because it already stimulates the intestines too much.
Allowed during intermittent fasting: Water with a shot of lemon, lime and some rock salt, as well as unsweetened tea, if necessary with fresh mint.
Although coffee has a small effect on hormones, it is still popular during fasting because of its antioxidants, as long as it is drunk pure. Especially when the intestinal cells are repairing themselves during the resting phase, even a shot of milk is counterproductive as it potentially contains allergens and fat13.
Whoever does sports during the lent can also drink a portion of amino acids. These should be sugar-free and contain no additives. Because amino acids are already split proteins, the intestine has no work with them and the fasting inhibiting reactions are so minimal that the effect is still maintained13. Sport or at least moderate exercise during the fasting period is important anyway, because it keeps the muscles intact and the body breaks down fat instead2. Strength training of maximum one hour and walks are most appropriate.
The facts about interval fasting summarized
Possible advantages of interval fasting:
✔ Detoxification processes in the body are promoted
✔ Chronic inflammation is eliminated
✔ Losing weight is supported (body fat reduction)
✔ Intestinal health is optimized: Recovery and regeneration of cells and digestive enzymes
✔ Hormone balance: blood sugar, stress hormones and the body's own hormone production
✔ More concentration & performance
✔ Time saving
✔ Acid and base balance is relieved and thus balanced
Possible disadvantages & challenges of interval fasting:
✘ Additional stress factor
✘ ravenous appetite (sometimes only in the initial phase)
✘ Challenge in everyday life (less spontaneity in social life)
✘ Incorrect timing can lead to muscle loss
Conclusion on intermittent fasting
Interval fasting is not just a trend, but a process that has been around since time immemorial and has many positive effects on our health and general well-being. Combined with a healthy nutrition and sufficient movement is chamfered an additional possibility for maximum health and efficiency in the everyday life.
1 Roth, Daniel (2018): Gesund und schlank durch Kurzzeitfasten. Riva Verlag.
2 Martin, Hans Helmut (2014): Volle Energie im Fasten. UGB forum spezial. S 10-14.
3 Enck, Paul und Frieling, Thomas (2017): Darm am Hirn. Freiburg: Herder Verlag.
4 Kreutzkamp, Dr. Barbara (2020): Intermittierendes Fasten – vieles spricht dafür. In: Medical Tribune.
5 Patrick, Dr. Rhonda (2019): Late-night eating and melatonin may impair insulin response. [https://www.foundmyfitness.com/episodes/melatonin-insulin-response; 12.06.2020].
6 Organic Workout (2019): Intervall-Fasten – die Lösung für alle Probleme oder doch nur Hype?
7 Dietze, G.; Wicklmayr M. und Mehnert: Physiologie des Hungerstoffwechsels.
8 Leitzmann, Claus (2018): Ernährung und Fasten als Therapie, herausgegeben von Rainer Stange.
9 Doccheck: Programmierter Zelltod [https://flexikon.doccheck.com/de/Programmierter_Zelltod?utm_source=www.doccheck.flexikon&utm_medium=web&utm_campaign=DC%2BSearch; 12.06.2020].
10 Fasten IM und Autophagie [https://www.klosterpernegg.at/methoden/autophagie-intervall-fasten; 30.05.20].
11 Bracht, Dr. Med. Petra (2018): Intervallfasten – Für ein langes Leben – schlank und gesund.
12 Hatori, Megum et. Al (2012): Time-Restricted Feeding without Reducing Caloric Intake Prevents Metaboli Diseases in Mice Fed a High-Fat Diet.
13 Patrick, Dr. Rhonda (2019): Fasting Q&A with Dr. Rhonda Patrick and Mike Maser.