In these months of isolation and “new normal” intermittent fasting has become fashionable again on social networks. And it is something that, as confirmed by health and dietetic experts, has its benefits for the body as long as it is done well and with sense. However, it can bring many problems and even be dangerous for people for whom it is contraindicated. And for everyone if it is not done well.

What exactly is intermittent fasting?

“It consists of leaving a window of time of one day in which no solid food is consumed or that provides calories in general, and another window of time, another day, in which all the necessary calories are ingested”, explains Daniel Mantas, director of NutriNour (experts in clinical, sports and personalized nutrition) and member of Doctoralia. “And there are several types of fasting 12-12, 16-8, 20/4 or 24h or 48h”

“The minimum for it to be considered that autophagy is taking place (a mechanism associated with fasting) is 12 hours of fasting,” as Mantas says. Let us examine the different modalities. These are the most common and used.

12:12 fasting (12 hours of feeding window and 12 of fasting). It is the most common, since many of us do it at night when, for example, we have dinner at 9:00 p.m. and go back to breakfast after 9:00 in the morning.
16: 8 fast or 16-hour fast, with an 8-hour feeding window and a 16-hour fast. An easy way to do this is by eating early dinner and delaying breakfast. For example, dinner at 20:00 and breakfast at 12:00. Or by cutting out dinner one day and not eating until you get to breakfast the next day.

Health benefits

As the director of NutriNour confirms, intermittent fasting can have positive effects on the body, “but it is important to know that it is not for all types of people,” he emphasizes. “It is important to assess our personal situation with a nutritionist to assess whether it may have contraindications. It is also important to say that fasting per se is not going to bring us health; It is also important what we choose at the time when we are going to eat food. ”

“That said,” Mantas continues, “during intermittent fasting there is a change in the substrate as an energy source because the body, not having glucose from food, uses triglyceride reserves.” “There is also an increase in growth hormone (this hormone decreases as we age), thus favoring the maintenance of muscle mass and bone density.” In addition, “it stimulates fasting-induced autophagy, a recycling mechanism by which cells use cellular components to obtain energy. This is related to a lower risk of contracting diseases and therefore promotes longevity ”.

“Intermittent fasting could have benefits on weight loss, cardiovascular biomarkers, aging and the intestinal microbiota,” says María Neira, nutritionist at the healthy recipes app Nooddle. “However, most of these results have been seen in animal studies. With the available human studies we cannot conclude that the practice of fasting is beneficial for health ”, he adds.

For his part, Salvador Ferrando, dietitian-nutritionist and head of the metabolic medicine unit of the Ricart Medical Institute, points out that “intermittent fasting is not suitable for people who suffer from certain pathologies or are at risk of malnutrition, but in general it is suitable for the healthy population, athletes and even type 2 diabetics. In his opinion, “it is not only good, but necessary”.

Does fasting promote weight loss?

It is especially interesting to clarify this point since many women are signing up for fasting in order to lose weight. And this can be counterproductive to your health and to the very goal of losing weight. “For weight loss, fasting can be recommended for people who are not usually hungry or for those who have anxiety about eating and tend to snack between meals, since if we propose to follow a protocol it can help us control the compulsive urge to eat” , says the director of NutriNour. “And also, by having a specific window in which we are going to eat, we can control what foods we choose and therefore improve our diet.”

In addition, Mantas points out, “a great advantage of intermittent fasting is that it is a simple strategy to carry out, easy to maintain in the long term and that we can carry out with different types of diets, that is, vegan, vegetarian, paleo …”. Although, as this expert warns, “it can cause a rebound effect if we use this protocol as a temporary thing and once the fast is over we begin to eat compulsively just because now we can do it whenever we want.”

“Fasting could promote weight loss through caloric deficit and a possible reduction in appetite, but its effects do not seem superior to those obtained through caloric restriction.” “Also, it is unclear whether periods of fasting could subsequently lead to people overeating at times of ingestion.”

According to the Nooddle nutritionist, “in the long term, the only thing that has been shown to be effective for weight loss is adherence to healthy lifestyle habits.” “Promoting strategies like intermittent fasting could distract people from what is really important: learning to eat healthy.”

Health hazards

Fasting that is too long, uncontrolled and without taking into account possible pathologies, can be dangerous for our health. “We must bear in mind that fasting does not mean not eating,” says Mantas, “it means eating the number of calories we need in a shorter window of time, and a window of time in which no solids or calories are ingested.”

“As we have seen,” this expert continues, “intermittent fasting is a very interesting practice due to the benefits it gives us, but we must be careful when we want to do it under certain conditions, such as the existence of pathologies or the performance of certain types of training. In these cases, Mantas advises you to always go to qualified professionals, such as a nutritionist dietitian. “Failure to do so can lead to some kind of fainting, general fatigue or sudden drops in blood sugar or tension” “The downside of all this is that, in addition, it can be a gateway to some types of pathologies such as anorexia nervosa, if not it does in a controlled way ”, he adds. Something that Neira also underlines: “Some studies suggest that intermittent fasting could favor eating disorders, as well as other mental pathologies such as depression, especially in people who have already suffered or who are more susceptible.”

In addition, Ferrando points out that it would also “be contraindicated for people with severe pathologies such as cancer, who suffer from type 1 diabetes or patients with pancreatic or hepatic pathology.”

For this reason, the three nutritionists point out the importance of a professional assessing whether or not it is correct to do some type of intermittent fasting. “I would not advise anyone to fasting or any type of diet without the advice and support of a dietitian-nutritionist”, Neira emphasizes.

Can you do some kind of fast that is not dangerous for your health? As Neira says, “fasts stimulated by feelings of hunger-satiety, that is, those that are born from listening to the body’s signals.” For example? “When we wake up without hunger in the morning it is better not to eat breakfast until we really feel like it. We can also put aside the idea of ​​not being able to go to bed without dinner. If there is no real hunger, the smartest and most beneficial thing to do is not do it. In this way we will be promoting a more intuitive and conscious diet, which is related to an improvement in our health ”, says the Nooddle expert.

Fasting and microbiota

The latest studies on the microbiota make it clear: our physical and emotional health depends on the bacteria in our intestines. In fact, the stomach is already referred to by experts as “the second brain.” Hence, more and more insistence from the medical and scientific field on the importance of taking care of our microbiota by eating an adequate diet and having good habits of life that keep us away from stress, a great enemy of the intestinal flora. As Xevi Verdaguer, psychoneuroimmunologist, scientific communicator, physiotherapist and author of Cuídate…. “To balance your body and transform your health, eating less and practicing intermittent fasting can promote the good state of our microbiota.” “Simply keeping a window without eating for 12 hours each day helps increase a type of bacteria that are very healthy,” he tells us.

The problem is that many times we eat too much and too badly. How does this affect our microbiota? According to Ferrando, “the problem is that we eat foods with a high glycemic load and every time we ingest less fibers, both soluble and non-soluble, which generates changes, causing firmicutes to grow and bacteroides (bacteria in our intestine) to decrease”. “This situation generates a pro-inflammatory microbiota that can greatly affect our metabolic and immune systems.”