Why people fast
Not all fasts are the same, because depending on which method is chosen, it is either about abstaining from certain food groups or a general reduction in food intake, which in turn results from different motivations. For example, the fasting month of Ramadan is important for devout Muslims and is one of the five pillars of Islam. During the religious fasting period, no food or drink is consumed between dawn and sunset. This is intended to strengthen the relationship with Allah and cleanse the soul of sins, as people concentrate particularly on prayer and the Koran during this time. In Christianity, there is a period of fasting between Ash Wednesday and Easter to prepare for the feast of Jesus' resurrection. Unlike Ramadan, there are no clearly formulated rules or rituals here - how or what is fasted is usually an individual decision, which can range from fasting for several days to abstaining from certain foods or now, for example, abstaining from media consumption.
Fasting is not a modern trend, but has been part of certain religions and cultures for centuries.
Fasting for health reasons
In addition to religious reasons, fasting for health reasons is becoming increasingly popular, especially nowadays. The aim is often stated as being to come to terms with one's own body, improve intestinal health or stimulate autophagy, i.e. the body's own cell cleansing. Weight loss is also often an argument for people who fast.
Therapeutic fasting
A centuries-old method of fasting is therapeutic fasting, which in its current form can be traced back to the doctor Otto Buchinger. While Buchinger recommended a fasting period of two to four weeks, the Ärztegesellschaft für Heilfasten und Ernährung e. V. (Medical Association for Therapeutic Fasting and Nutrition ) recommends a period of seven to ten days. Therapeutic fasting begins with a reduced calorie intake of 1000 kilocalories. Addictive substances and stress should also be avoided. On the fasting days, a maximum of 500 kilocalories per day may be consumed in the form of juices sweetened with 30 grams of honey or broth. The fast is then broken by slowly increasing the calorie intake with certain, usually vegetarian, foods. According to Buchinger, therapeutic fasting also has a spiritual and psychosocial effect, as the fasting person reduces external stimuli.
Intermittent fasting
Well, where are the fasting people of the 21st century? Intermittent fasting, of course. This type of fasting has been a recurring theme in the media for several years, almost hyped, especially in relation to autophagy and weight loss. But first, we'll tell you about the best-known time slots within this form of fasting:
- The classic 14:10 or 16:8 fast means fasting for 14 to 16 hours a day, leaving an eight to ten hour window for food intake. This usually involves skipping either breakfast or dinner. Incidentally, this type of intermittent fasting is almost identical to that of Ramadan.
- The 5:2 method means that you eat normally five days a week, while two days a week you eat a maximum of a quarter of the usual amount of calories.
- In alternate-day fasting, only around 25% of the other calories are eaten every other day.
Intermittent fasting is primarily intended to stimulate autophagy. It is often argued that this occurs after twelve hours of fasting. This may be true, but it must also correlate with a consistently low insulin level. Then the glucose stores from liver and muscle cells are targeted first, then the fat cells and only at the end is autophagy used as a means of energy production. It is therefore possible that autophagy occurs after twelve to 16 hours, but the exact number of hours probably varies from person to person. In addition, the full effect of autophagy only occurs after 48 to 72 hours, during which time cell renewal also takes place. This is why the probability of autophagy occurring during a ten-day fasting cure is high, as a maximum of 500 kilocalories are consumed over a longer period of time, which inevitably keeps insulin levels low. Whether autophagy occurs even after twelve to 16 hours of intermittent fasting has not yet been conclusively proven.
Fasting: Worth the hype?
This cannot be said across the board. This is because human clinical studies in the field of fasting are not so common, as the research field is still in its infancy. While animal studies show, for example, that the risk of type 2 diabetes mellitus, cardiovascular disease and cancer can be reduced by intermittent fasting, this has not yet been proven in human studies. Rather, there are reviews on how fasting could affect health. In terms of reducing fat-free mass, however, intermittent fasting appears to be more beneficial than a "normal" diet, as more muscle mass is lost in comparison. It should be noted here that you have to be in a calorie deficit to lose weight, even with intermittent fasting. However, for many people this happens automatically, as the smaller time window for food intake means that they usually eat less.
Intermittent fasting can lead to the well-known yo-yo effect, as the basal metabolic rate decreases during the fasting period and you eat too much if you do not slowly increase your calorie intake.
However, the major claims regarding fasting, i.e. cell renewal, disease prevention, increased cognitive performance and even rejuvenation of the body as claimed by some, cannot be confirmed by nutritional science.