Is normal for 2 days

Eat only every other day : Researchers find no side effects from strict intermittent fasting

Of all the methods that promise longer and healthier lives, one is particularly promising. It's called: Eat half! But because very few manage to do this in the long term, scientists (and those willing to lose weight) are looking for other methods. One of them is intermittent fasting, i.e. not eating anything for a certain period of time. However, this is viewed critically again and again because there is little data on the long-term effects.

Scientists from the University of Graz have now put their test subjects on a strict interval diet for a study. They studied the effects over four and six months. In the journal "Cell Metabolism" they now report that the participants consumed significantly fewer calories and lost weight on such a diet. It also has health benefits. Side effects did not occur.

The researchers led by Slaven Stekovic from the University of Graz divided 60 healthy subjects of normal weight into two groups for their study. Half were allowed to eat as much as they wanted, the other 30 participants had to adhere to a rigorous diet for four weeks. They had to alternate between fasting for 36 hours - one day and two nights - after which they were allowed to eat normally for twelve hours.

To make sure they didn't eat anything during Lent, the researchers monitored the participants' blood sugar levels. To assess the safety of the method, the scientists also examined 30 other people who had been eating according to such a strict plan for at least six months.

A third fewer calories

It found that while participants were allowed to eat some of the calories lost during the fast during the twelve hours they were allowed to eat, they did not catch all of them. On average, fasting subjects consumed 37 percent fewer calories than before and lost 3.5 kilograms of body weight during the four-week test period.

In addition, blood tests found various values ​​that the researchers associate with improved cardiovascular system and increased longevity, such as lower cholesterol levels and a decrease in fat tissue in the abdominal area. Studies have shown that it is precisely this belly fat that correlates with the risk of cardiovascular diseases.

In other studies there had been indications that such a strong calorie reduction could lead to decreased bone density or weaken the immune system. In the Graz study, however, there were no side effects in the test subjects even after six months.

The researchers conclude that the method is safe (at least for this period) and speculate that alternating fasting even has the potential to become the standard in the clinic, for example when obese patients are supposed to lose weight. They also suggest it as a preventive health measure to prevent cardiovascular diseases, for example.

The big advantage over a conventional reduction in calories is not having to laboriously count calories, but can simply stick to not eating on certain days.

Criticism of the study design

Jürgen König is rather skeptical: "It was to be expected that a reduction in energy would have some positive health effects," says the head of the Department of Nutritional Sciences at the University of Vienna. Whether these effects came about through alternating fasting cannot be said on the basis of the study design.

In the study, for example, there was no control group that achieved a calorie reduction similar to that of the fasting participants through continuous (instead of intermittent) fasting. This was the only way to really make a statement as to whether the method of intermittent fasting and not the calorie reduction itself would have had the effects.
This criticism is also cited by Stefan Kabisch, study doctor at the German Institute for Nutritional Research (DIfE) in Potsdam-Rehbrücke. It has been known for decades that calorie reduction has positive effects. He criticizes the methodology of the study sharply, even attests to it "no usable new findings on intermittent fasting in humans".

Intermittent fasting could make your metabolism more flexible

Annette Schürmann, Head of the Experimental Diabetology Department at DIfE, is not that critical of the matter. It is true that one cannot deduce from the data that the effects found are really caused by intermittent fasting and not fundamentally by the reduced calorie intake. "Results from animal studies suggest, however, that breaks in intermittent fasting could have a positive effect in addition to the known effects of reduced calorie intake," Schürmann told Tagesspiegel.

For example, compounds (ketone bodies) are formed in lipid metabolism, which are said to have beneficial effects on the cardiovascular system. In addition, the body can better switch from carbohydrate to fat metabolism through the breaks, which leads to the burning of belly fat. A higher sensitivity to insulin, which is observed during intermittent fasting, can also protect against diabetes.

The data for this come mostly from animal experiments, since studies on humans - as is often the case in nutritional research - are very complex and difficult to carry out. "In this respect, it is thanks to the Graz researchers to have demonstrated the safety of this strict type of intermittent fasting," says Schürmann.

"Think about what to fast for"

Further studies should now follow, for example to check whether alternating fasting is suitable for treating overweight patients. An American study had shown in 2017 that this method of weight loss is difficult for patients to maintain in the medium term. Even after several weeks of alternating fasting, patients sometimes report that they are very hungry.
Schürmann does not advise anyone to follow such a strict intermittent fasting as in the study. You should definitely discuss this with your family doctor beforehand. Intermittent fasting in the mode 16: 8 (16 hours a day nothing to eat) or 5: 2 (five days of normal eating, two days a maximum of 600 calories) can be tried, however. However, she does not recommend this to children and adolescents without weight problems or pregnant women.

It is always important to consider why you choose intermittent fasting. "If you really want to lose weight, you shouldn't just eat fast food when you're allowed to eat," says Schürmann. Because if you get back to the normal number of calories, you won't gain anything. The researcher says: "Reducing calories is still the biggest factor in weight loss." And whether intermittent fasting helps, it differs from person to person. (with smc)

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