Overweight obese children can fast longer
Intermittent fasting: eating with a watch
What is the truth of the hype about intermittent fasting? There is hardly a kiosk that doesn't advertise it. One hopes for easier weight loss, the other also for the prevention of dementia and cancer. But the evidence for this is - as is not uncommon - rather meager if you take a closer look.
Fat mice get slim when put on a diet. Most people don't. Calorie restriction works in cages and in closely supervised clinical trials. In everyday life, diets fail with great regularity - at the latest when the dreaded yo-yo effect occurs. Intermittent fasting promises better adherence.
The principle: overweight people who want to lose weight only temporarily go without food - depending on the fasting method, 16 hours a day, 2 days a week or every other day (see box). Otherwise you can eat normally. The cabaret artist and doctor Eckart von Hirschhausen propagated intermittent fasting in Stern last year. This apparently appealed to the readers in such a way that the method was again the title in the first issue of 2019.
Intermittent fasting as an all-rounder
Intermittent fasting is so popular not least because it not only promises shedding pounds without hunger and the yo-yo effect. The effects propagated in numerous guidebooks and media reports also include protection against diabetes, cardiovascular diseases, Alzheimer's and cancer. Intermittent fasting is said to give people a longer life.
There is scientific evidence for all of these benefits of intermittent fasting - from experiments on mice, rats, and some rhesus monkeys (1). Human studies are small and rare. The most common form of intermittent fasting, the 16: 8 method, has so far been used by around 300 people. The 5: 2 method has been researched a little better - but with sometimes sobering results.
Dr. Tilman Kühn, head of the HELENA study carried out at the German Cancer Research Center in Heidelberg, reports: “There was no difference between the group that fasted intermittently and the group that followed a conventional reduction diet (2). And not only with regard to weight reduction, but also with all metabolic parameters. "
A total of 150 overweight or obese test persons had Kühn and his team followed the 5: 2 method of intermittent fasting or a conventional diet for 12 weeks. In both groups the calorie reduction was 20%. A third group of subjects served as controls. They were advised to have a balanced diet, but they did not need to reduce their caloric intake. The 12-week intervention phase was followed by 38 weeks in which the weight and health of the study participants were observed. After 12 weeks, the interval fasters had lost 7.1% of their body weight, a little more than the subjects who had been on a conventional diet (−5.2%). But after just under a year there was no longer any significant difference between the two groups.
Two other studies from Norway and Australia, also comparing a 5: 2 fasting and a conventional weight loss diet, came to identical results (3, 4).
Perseverance while losing weight
The problem is well known: “Just because something works in animals doesn't have to work in humans,” says Kühn. The Heidelberg nutrition epidemiologist sees yet another reason for the obvious discrepancy between expectation and reality: “The small human studies that have existed so far often did not include a suitable control group that followed a conventional diet. Only our study made this comparison possible. "
Kühn interprets the result positively: "The study shows that intermittent fasting is no worse than a conventional reduction diet and could be an alternative for some people who find it easier to temporarily reduce calories." goes hand in hand with better adherence?
For Prof. Dr. med. Andreas Michalsen, chief physician of the Naturopathy Department at the Charité-Universitätsmedizin Berlin, this aspect is even decisive, because: "Intermittent fasting had the same effect as a conventional reduction diet, but which is rarely followed in everyday life." goes hand in hand with better adherence, but is still open. Initially and under close supervision, the study participants did the 5: 2 fasting well, ”reports Kühn.
But in the follow-up period, hardly any of them actually adopted intermittent fasting as a lifestyle. However, this could be due to the fasting method investigated. "It is possible that 5: 2 intermittent fasting is not the optimal method of intermittent fasting", Kühn sums up from his study. In fact, the 16: 8 method currently seems to be more popular in Germany. The advantage: a large part of the daily fasting period is overslept.
This not only affects adherence, but could also influence the effectiveness of fasting: "Chronobiological mechanisms that play an important role in the positive effects of intermittent fasting are only served with the 16: 8 method," explains Michalsen. The study data on this form of intermittent fasting in humans are meager, but impressive: In 2014, Czech researchers reported on a small group of diabetes patients who received the same number of calories for 3 months either in the form of 6 meals spread over the day or in the form of 2 meals Breakfast and lunch - ate. Intermittent fasting performed better in all study endpoints - weight loss, liver fat, insulin resistance, beta cell function (5).
In contrast to diabetes, the findings on cardiovascular diseases, neurological disorders and cancer have so far been limited to experiments on mice. It was they who sparked the enthusiasm for the effects of intermittent fasting.
The fat and the thin mouse
7 years ago, US researchers published a photo of two black mice in Cell Metabolism: They were the same age, came from the same breeding line, had not moved in the same way in their lives and always received exactly the same amount of food. But one mouse was slim, the other fat.
The difference: the slim mouse was only allowed to eat its food ration for a limited period of time each day, whereas the fat mouse was allowed to eat whenever it wanted (6). Apparently, the researchers concluded, it had to be the timing of food intake that kept the animals lean or made them fat. And it got even more impressive: Several studies on mice show that animals with cancer live longer if they are allowed to fast temporarily.
At the forefront of research on intermittent fasting in cancer is the US physician Prof. Dr. med. Valter Longo from the University of California at Los Angeles. In an animal model, he showed that fasting slows tumor growth and causes differential stress resistance that protects healthy cells from the effects of high-dose chemotherapy - but not cancer cells (7).
These results made waves, even as far as Heidelberg, where Kühn's clinical colleagues were confronted with patients who asked whether they should intermittently fast during their cancer therapy. "That gave us the idea to conduct a study to investigate what is really true about intermittent fasting - initially on healthy overweight people," reports Kühn.
Fasting cancer patients is considered tricky, oncologists in particular are skeptical, as cachexia and malnutrition are common complications. And Michalsen, too, suddenly sit across from patients who want to support their cancer therapy with food abstinence or who have already started intermittent fasting on their own.
For the Berlin physician, it was "very unfortunate that intermittent fasting was very much hyped in the media before there was sufficient scientific data from human studies". Michalsen is convinced that “there is something to intermittent fasting”. In a pilot study, Michalsen's team has already succeeded in showing that cancer patients can benefit from a fasting intervention (8).
Women with breast or ovarian cancer who avoided food 36 hours before and 24 hours after chemotherapy suffered less fatigue and had a better quality of life. Two larger studies - again in patients with breast and ovarian cancer and also in patients with prostate cancer - are currently underway.
It is a careful approach to fasting in the context of cancer. Because even if the calorie intake is not restricted, any type of intermittent fasting automatically leads to a reduction in energy consumption, as Michalsen reports. With 5: 2 fasting and “alternate day fasting” by around 15–20% and with 16: 8 fasting by around 10%. For overweight people this is one of the interesting aspects of intermittent fasting, but of course not wanted for cancer patients. "In cancer, however, this does not seem to lead to weight loss; at least this was not observed in our pilot studies," explains Michalsen.
Nevertheless, unwanted weight loss is one of the safety parameters in the currently ongoing studies. For a larger study in which intermittent fasting according to the 16: 8 method is to be examined, the funds have already been applied for. In further studies, Michalsen and his working group are currently testing a combination of initial therapeutic fasting and subsequent intermittent fasting for multiple sclerosis and rheumatism. In studies, it has meanwhile become established to combine periodic fasting and intermittent fasting, explains Michalsen.
Trigger the metabolism
Ultimately, it is a matter of activating the mechanisms that are effective during fasting, namely fat breakdown, the production of ketone bodies, autophagy, the effect on the microbiome or stem cell production. And this is achieved through intermittent fasting - short-term fasting with high repetitions - as well as through periodic fasting over longer periods of time.
The health benefits of intermittent fasting will likely differ depending on the illness. "In MS, it is probably the ketone bodies, in rheumatism the autophagy and the effect on the microbiome, and in cancer the downregulation of IGF-1 and mTOR that could have a positive effect," says Michalsen.
Certainty about the extent to which patients actually benefit from intermittent or periodic fasting will ultimately only be shown by further and larger human studies that are currently starting or are already running, but whose results are only expected in 4–5 years. Nadine Eckert
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Strict and less strict intermittent fasting
Intermittent fasting can be done in different forms. In the most common form, the 16: 8 fasting, food is only consumed in a time window of 8 hours a day; the rest of the time there is no eating. The waiting period can also include the night. Often either breakfast or dinner is avoided. You should and may always drink as long as it is calorie-free.
With 5: 2 fasting, on the other hand, people eat 5 days a week without major restrictions, while food intake is limited to a small amount of around 500 calories on 2 days - a light dish made from chicken and vegetables, for example. The two fasting days should not be consecutive.
The strictest variant is the so-called Alternate Day Fasting (10 in 2), which fasts every other day, again with a maximum calorie intake of around 500 calories (graphic).
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