Intermittent fasting: is the scientific evidence for or against it?

Although there are many studies on the possible benefits of intermittent fasting on health, the lack of adequate control groups and homogeneity in the protocols makes it difficult to reach a scientific consensus on the matter. Inés Mármol, researcher at IIS Aragón, talks about this fact in this article in Heraldo de Aragón

Christmas is, for many, synonymous with joy. Reunions with loved ones, bright lights on the streets, beautifully wrapped gifts and a few days of vacation, which are always appreciated. On these holidays, good food figures prominently. We are going to snack on chocolate and churros, to the company dinner and we gather with our relatives around a roast tray with potatoes, a good handful of canapés and an assortment of nougats as the final touch.

However, this succession of delicacies can produce remorse, guilt and dissatisfaction in many people. I shouldn't have eaten that powder, I should have had less potatoes for dinnerIt would have been better to order a salad instead of the torrija with Iberian ham. The fear of gaining weight is an unpleasant gift that many find under their tree on the 25th, even if it was not included on their wish list. This anguish can overshadow the joy of the holidays and fill New Year's resolutions of 'joining the gym' and 'starting a diet.'

Regarding the latter, a diet to lose weight should be prescribed by a professional who studies each particular case. However, the most common thing is to turn to the Internet doctor. Although we can find reliable and very useful information on the Internet, there are also hoaxes disguised as science so carefully that they can confuse us. When it comes to food, in January pages and pages appear, as if brought by the Three Wise Men themselves on a camel, to help us rescue our bodies after the holidays. Purifying broths, miraculous infusions, detox smoothies and other 'detox' diets.

Intermittent fasting in the media

The benefits of intermittent fasting have been widely advertised for a few years through various media. That it is great for losing weight, that it improves blood pressure, that it helps your intestinal microbiota to be healthier... All of this supported by a lot of scientific studies. Besides, It has the advantage that doing it is very easy, since all you have to do is not eat for a while, which can be a whole day or a few hours each day. No more leaving your monthly salary on kale that you don't know how to cook.

Unfortunately, when something is presented to us in such an idyllic way, our spider sense should be activated, because it is very possible that there is a cat in the bag. In the case of intermittent fasting, the cat is the size of a Bengal tiger, since there is no scientific consensus on the matter. That is The scientific community, after analyzing all the data available to date, has not been able to reach a clear conclusion about whether it should be recommended or not.

Because yes, it is true that there are many works in which the effect of intermittent fasting on health has been investigated. And it is also true that in some of them an improvement in blood pressure or the composition of the microbiota has been observed, as well as that it can help lose weight. Yes indeed, Not all that glitters is gold.

Firstly, Most of what we know about the effects of intermittent fasting is based on experiments with laboratory animals.. Although this is not a bad thing, as experimental animals are one of the cornerstones of modern scientific knowledge, we cannot happily extrapolate the results to humans. That is to say, just because something happens to a mouse does not mean that it will happen to a person. For example, several studies using experimental animals have concluded that intermittent fasting could improve cognitive function. 

However, human studies are not as conclusive. Therefore, today and with the data in hand, It cannot be said that intermittent fasting prevents Alzheimer's or other neurodegenerative diseases. That does not prevent many media outlets that advertise intermittent fasting from including among the arguments in favor how great it is for cognitive function. They keep quiet about the fact that, for now, it has only been seen in animals. Fact kills story.

Intermittent fasting in science

Although the issue of cognitive function is still to be resolved, other studies carried out with human volunteers have managed to corroborate previous studies in animal models. For example, some studies have concluded that Intermittent fasting could help control weight and also modify the composition of the microbiota. However, even when we have studies that support a hypothesis we encounter problems. Many of these works do not have an adequate control group. That is, it is not compared to a group of volunteers who do not follow intermittent fasting. This makes it difficult to draw definitive conclusions, since one cannot be absolutely certain that these observations are due to intermittent fasting.

Another of the big problems with studies with human volunteers is the lack of homogeneity: they are not carried out under the same conditions. Each study tests one type of intermittent fasting. There is the 5:2 model, in which you fast for two days and the rest you eat normally or the 16/8 model, in which you fast for 16 hours a day and for the remaining 8 you eat and drink normally, among other options. Since the same protocols have not been followed, it is not correct to compare the results obtained in each case. This makes it difficult for a health or nutrition professional to recommend someone try intermittent fasting, because which model is the most suitable?

Finally, In each study we work with volunteers with very different characteristics. Many of them focus on evaluating the effect of intermittent fasting on people with some pathology, such as type 2 diabetes or nonalcoholic fatty liver. Therefore, it would not be correct to assume that healthy people will respond the same. And the same happens with studies carried out with healthy people, the results cannot be extrapolated to people with any disease.

Therefore, the scientific community cannot reach a consensus on whether or not intermittent fasting is beneficial for health. The first tests seem to indicate that it would be, but more studies are necessary and homogeneous protocols must be followed. That's why, Be very careful if, after the holidays, you find yourself tempted by one of those articles that sell you intermittent fasting as the solution to all your problems. Any serious nutritionist would tell you that staying healthy all year round, exercising and following a diet rich in fruits and vegetables will be much more effective than any miracle remedy. And I would also tell you to enjoy nougat and canapés without regrets, because health is a long-distance race and not a sprint: what you do the other 360 days of the year matters much more than what happens during the five days of Christmas meals .

Source: Heraldo de Aragón