Truths and illusions around intermittent fasting | The weekly country

The tradition of fasting goes back a long way in different cultures and religions—Lent among Catholics, Ramadan for Muslims—and even Hippocrates, the father of modern medicine, wrote: “To eat when you are sick is to feed your illness.” Caloric restriction practices have always been present in popular culture, but in recent years they have jumped from religious fiefdoms to settle on the street, sponsored by the social modism of networks and the growing scientific interest in its potential effects on health. Hello Between fashion and science, dancing in an eternal controversy, the so-called intermittent fasting is now growing, a phenomenon with healing potential on paper, but little evidence in real life.

The actress Gwyneth Paltrow, a devotee of this practice, has coffee for breakfast, bone broth at noon, and vegetables for dinner very early, as she herself explained in the podcast The art of being well (The art of being well). It is his method, but not the only one. There are different fasting patterns and each individual, within those eating programs, eats what he considers. The most common intake and abstinence models, however, are the so-called 5/2 —stopping eating two (alternate) days a week— and 8/16, which consists of concentrating meals on eight hours a day and fasting the rest It is assumed that in these alimentary dynamics there is some caloric restriction, although it may not happen if, for example, a person eats in their eight hours except the same calories that someone who does not fast takes throughout the day.

A practical diet is delivered for the benefit of health, since most of the metabolic state is, greater well-being and weight reduction. Also potential to treat diseases, such as diabetes or cancer. But beyond the noise of social networks, there are controversies and conflicting positions among the scientific community. “There is suggestive evidence in experimental models, but we have no evidence in the human case. The information that exists is interesting, but insufficient in humans”, sums up Antonio Zorzano, head of the Complex Metabolic Diseases and Mitochondria laboratory at the Barcelona Institute for Research in Biomedicine (IRB).

The hypothesis of the possible bonanzas of intermittent fasting come from animal experimentation. “There is a lot of accumulated information that, if you, an animal, restrict calories to 70% or 50% of what it used to eat, what happens is that it is metabolically healthier and lives longer,” Zorzano points out. If the animal eats less, if calories are chronically restricted, it gains less weight, has less adipose tissue, and this lower adiposity improves other parameters: it has less resistance to insulin and uses more fatty acids instead of glucose to produce energy (ketosis). ).

But all this cascade of metabolic phenomena is not so easily reproduced in humans, agrees Francisco Botella, coordinator of the Nutrition Area of ​​the Spanish Society of Endocrinology and Nutrition: “For a human being to develop ketosis, many more hours have to pass, and it is hardly ketosis is achieved with intermittent fasting cartridges.” A scientific review published in the dedicated journal New England Journal of Medicine acknowledging that while intermittent fasting “improves health throughout life” in animal models, “it remains to be determined whether people can sustain intermittent fasting for years and potentially accrue the benefits seen in animal models.”

hypertension and glucose

The experts consulted agree that where the evidence is clearest —although limited— is that with intermittent fasting you can lose some weight and, associated with it, slightly lower hypertension or glucose levels. “But this metabolic benefit has not been shown to imply a change in quality of life or mortality. There are no studies for more than a year”, adds Botella.

The lack of long-term research in humans hampers the ability to make recommendations. “The principle of prudence tells me that we wait. For example, we know that there is a relationship between muscle strength and longevity: with age, muscle mass decreases and sarcopenia arrives. [pérdida de masa, fuerza y funcionamiento de los músculos]. I would like to be sure that this type of dietary manipulation does not modify the ability to have muscular strength”, agrees Zorzano. It has been described that fasting can also cause weakness, dehydration, headaches, difficulty gaining weight, low blood pressure or fainting.

Jordi Salas-Salvadó, a researcher at the Rovira i Virgili University of Tarragona and an eminence in the study of the Mediterranean diet, adds that intermittent fasting is a practice that is “difficult to maintain over time.” Botella agrees: “It may be compatible with the new social life. Outside of rehearsals, the abandonment is very high ”.

Valter Longo, biochemist and one of the great defenders of intermittent fasting, dissected in an article in Nature Aging the available scientific evidence and highlighted that, according to human research, this dietary technique “improves sleep, attenuates the deterioration of cardiac performance induced by age and diet, and improves blood pressure and lipid accumulation.” But he noted no potential adverse effects and suggested: “The use of this type of intervention should be limited to short periods and applied only to people with conditions in which regular intermittent fasting has been shown to be effective.”

It is not valid for everyone, the voices consulted agree. It is contraindicated in pregnant women, people who have undergone bariatric or stomach surgery, people with some underlying pathology, such as kidney failure, or individuals who are vulnerable to an eating disorder. “The great danger is that someone with a contraindication practices it and we then find ourselves with malnutrition in a cancer patient, a serious accident in a diabetic person or hypoglycemia with kidney failure,” says Botella.

Starve cancer to death

Cancer is one of the fields where intermittent fasting seeks to claim itself. Longo is precisely one of the great defenders of the role of this practice in oncological conditions. His hypothesis on paper is striking: he proposes to starve cancer to death. “If a cancer patient is deprived of food before undergoing chemotherapy, normal cells will respond by putting up a protective shield; On the other hand, the tumor cells will disobey the order to protect themselves and will be vulnerable, they will allow tumor cells to be eliminated while the damage to the healthy ones is reduced ”, he refers to in his book fasting against cancer. But oncologists call for prudence.

Juan de la Haba, member of the Spanish Society of Medical Oncology, admits that mechanistic explanations are addictive, but that one must be cautious in real life. “It is justified because the tumor cells have a greater caloric need and less capacity to adapt to the restriction, and the healthy cell has a lower caloric requirement and adapts better to the caloric restriction”, he points out. But the evidence is very limited: “We have studies in rodents that justify it, there is a very good preclinical line. But in the laboratory we have cured cancer for a long time. In epidemiological studies, fasting has some relevance, but there are conflicting results. There is no solid scientific basis to make recommendations to patients.

The process is more complex than it might seem and influences many variables. “In tumors, not all tumor cells are at the same metabolic rate. Those with rapid cell growth have a high metabolic rate, but usually respond well to chemotherapy. Tumor heterogeneity and that of the population is so great that a mechanism as general as caloric restriction is a strategy doomed to failure”, settles the oncologist.

These practices can even be counterproductive for patients. Some, who already have sarcopenia and cachexia (loss of weight, muscle mass and weakness), fast and lose more weight, which can aggravate the condition. “Food also plays an important role in the state of physical, mental and emotional well-being of the patient. And, sometimes, eating a piece of cake is accompanied by a feeling of guilt because he thinks that his illness is going to get worse ”, laments De la Haba. And he adds: “It involves a personal sacrifice and is usually accompanied by the purchase of supplements that are not usually cheap.”

Salas-Salvadó agree that, in cancer, the evidence is “little and the studies are few.” And she advised: “There are many talkative people who can sometimes do harm because people with cancer are looking for a miracle.”

What happens, triumphs or is verified in the laboratory with animals is not always replicated in the lives of humans. From a biochemical point of view, the experts found, the possibilities of intermittent fasting are “tremendously exciting,” but not all of the features later translate into benefit for the patient. In the scientific world there are many doubts to be resolved. Starting with assuring whether intermittent fasting is a real benefit for the patient. And, if so, which type is the best, for how long, with what food, who would benefit… Salas-Salvadó admits his reservations: “I am completely skeptical. I seriously doubt this will have any long-term enhanced effect. But I find it super interesting.”