Intermittent fasting? Yes thank you, actually no. Talk to science
The different fasting practices conquer an ever greater space in the reality of people looking for strategies to keep fit and healthy. Intermittent fasting then has a particular charm. But here's what science thinks about it, also with regard to its social and psychological effects. Extract from an article by Camilla Orlandini of Scienza in Rete
The words "intermittent fasting" have been burning hot in the last two weeks, since the immunologist-celebrity Antonella Viola, in anticipating the contents of her new book, declared that she has been practicing a form of intermittent fasting for two years (TRE, Time Restricted Eating ) not only to regulate one's weight, but above all as a tool for well-being and longevity. But it's not just the words of Antonella Viola or nutrition experts, who have spoken out on the matter in recent days, that make intermittent fasting a topic as topical as it is controversial. Between books for the public and applications for smartphones, the various fasting practices are gaining more and more space in the reality of people looking for strategies to keep fit and healthy. Intermittent fasting then exerts a particular charm, because unlike the classic diets of continuous caloric restriction, it seems paradoxically less rigid and taxing. “It seems”, in fact: «The risk is that these fasts open the door to actions harmful to the state of health; people risk undertaking a form of fasting on their own, without the guidance of a specialist, subjecting themselves to strong caloric restrictions and then continuing to eat unbalanced or unhealthy meals, which remain harmful, despite the fasting period» comments Mauro Serafini, professor of human nutrition at the University of Teramo and member of the 2003 group for scientific research. And when it comes to nutrition, the undisputed protagonist of our daily lives, there are other factors to consider, such as the social and psychological effects: the four directors of the Medicine degree course at the University of Padua warn «Intermittent fasting is associated scientifically significant, especially in young women, to psychopathological eating disorders» and they add how skipping dinner several times a week corresponds «to depriving a family of an important ritual (…) with possible deleterious implications for children and the family itself. Not having dinner together to adhere to diets that involve skipping the evening meal risks creating isolation ».
But in a world where obesity and overweight affect 39% of the population , intermittent fasting is attracting interest, including from the scientific community, as a potential intervention strategy; the question that arises is: how much – and “only” – potential?
Intermittent fasting: an identity problem
The term intermittent fasting indicates different types of nutritional interventions that are "freely" inspired by the concept of fasting, i.e. the total abstention from food, and any caloric intake, continued over time. Thus a real (or prolonged) fast is distinguished when the 48 hours of abstention are exceeded, and an intermittent fast, when the intervals are shorter. In particular, the latter is divided into three main categories: fasting on alternate days (or alternate day fasting , ADF); fasting for two days a week, consecutive or not, (also known as the 5:2 diet); and Time Restricted Eating (TRE, or TRE), which involves getting your entire daily caloric intake in a narrow window of the day (from 10 hours with 14 hours of fasting, to the most demanding 4 hours with 20 hours of fasting). But the differences don't end there; the THREE can refer to a precise interval of time in which to eat, such as in the morning or in the afternoon, or to leave the person free to choose. There are also versions of interventions where, in the fasting window, a minimum caloric intake is still prescribed (from 400 to 800 kcal).
It therefore appears evident, as in all these different declinations, the term "intermittent fasting" is lost and confused in meanings. This variety follows a characteristic inherent in the literature on the subject: in a still "adolescent" scientific field, the trials on human beings that support or refute the beneficial effects of fasting rarely agree on terminology, returning for each "intermittent fasting" a collection rather scarce and contradictory data, which struggles to be evaluated collectively.
Promises from the animal world
After almost a century of research on animal models, calorie restriction, understood as a 20-30% reduction in daily intake, is definitively associated with an improvement in overall health, from mice to non-human primates. The reduced caloric intake over time reduces the major risk factors and the incidence of cardiovascular, metabolic, neurodegenerative diseases and certain oncological diseases. As far as the different forms of intermittent fasting are concerned, the positive results , although “younger”, are similar: alternate day fasting, 5:2 and TRE fasting report clear and consistent results with regards to weight loss, the reduction of risk factors and the improvement of the glycemic, lipid and inflammatory profile.
And that's not all: a restricted diet in 8 hours (with 16 hours of fasting) and aligned with the period of greatest activity of the animal, seems to have positive and protective effects in mice regardless of weight loss. The results are in line with the logic of circadian rhythms: organisms have evolved by developing an internal clock that organizes physiological, metabolic and hormonal responses so that each process is implemented in the optimal time interval; therefore there is a time to eat, move and concentrate and a time to repair and rest. Aligning caloric intake with the moment of activity, in which the metabolic response is most efficient, seems like a sensible logic to get the most out of nutrients, and the data prove it. And yet, with the human being the story – and the physiology of the organism – becomes more complicated.
And in the human being? Inconsistent data
Given the promising results in animal models, scientific research has moved to humans, conducting trials to verify the effectiveness of interventions both on weight loss and on the improvement of cardiometabolic risk factors. Several reviews and meta-analyses of the scientific literature conducted in recent years, performed taking into consideration only randomized controlled trials (the gold standard of scientific research) all report the same result: there is not enough data; the subjects are few and the intervention period is too short (often involving from one to three months, rarely reaching six or twelve). “The number of diet books encouraging the incorporation of fasting into our lives is several orders of magnitude greater than the number of trials examining whether fasting should be encouraged in general,” write the authors of a 2020 review on the effects of intermittent fasting on metabolic health.
The current scientific literature, for its part, reports conflicting results. In most of the trials , but not in all, the different fasting strategies lead to a reduction in body weight, since they are often associated with a consequent caloric restriction, but on the contrary, in isocaloric conditions, i.e. if subjects undergoing intermittent fasting (every other day, 5:2 or THREE) consume the same amount of calories as a control group, in most cases the effects on weight seem to disappear. Even with regard to cardiovascular or metabolic risk markers (such as triglycerides, cholesterol, insulin or blood sugar) the results differ: «According to some studies there would be a significant improvement compared to control groups, while others find no differences or only identify some effects » explains Mauro Serafini, who comments: «This variability could be linked to the categories of intervention: when the subjects are of normal weight and have normal values, fasting has no noteworthy effects, while if the population has altered baseline values and a excessive body weight, interventions lead to significant results.
However, when you compare alternate day fasting, 5:2 and THREE with a typical 20-25% calorie restriction, the data becomes even more conflicting. According to a meta-analysis published in 2022 in Frontiers in Nutrition , which analyzes 43 randomized trials, with a total of 2483 participants, the different forms of intermittent fasting lead to an improvement in body weight and insulin response compared to a control group without intervention , while they show no difference when compared to a calorie restriction. As regards weight loss in obese subjects, however, a meta-analysis also published in 2022, reports how both alternate day fasting and the 5:2 diet have proven to be more effective than the classic caloric restriction in decreasing the weight of the participants, but without influencing dyslipidemia or glycemic response. In its conclusions, a recent meta-analysis by Nature Endocrinology with respect to the effects of different forms of intermittent fasting declares: «The degree of weight loss is equal to that obtained with traditional calorie restriction approaches. The impact on cardiovascular and metabolic risk parameters is still uncertain. While some studies have shown improvements in blood pressure, LDL, cholesterol, triglycerides and insulin resistance, others have shown that these positive effects do not occur.
Even considering only Time Restricted Eating (TRE), the data remain equally conflicting: A 2023 meta-analysis including only randomized trials of 16-, 14-, and 12-hour fasting TRE interventions in overweight participants reported that the only differences between the intervention group and the control (who assumed the same caloric intake) were greater weight loss and better diastolic blood pressure, with no effect on metabolic risk factors or reduction in dyslipidemia, while the New England Journal of Medicine last year he wrote how, after a THREE with 16h of fasting, no parameter, not even weight loss, was better than a continued calorie restriction. Furthermore, if the TRE intervention, even more extreme with 20 or 18 hours of fasting, is carried out on people of normal weight, it does not seem to lead to any significant improvement, either in terms of weight or in terms of health, especially if in the evening. The only rather recent results , which seem to be consistent with each other , concern a TRE intervention in which the morning eating window, associated with a calorie restriction, in prediabetic male patients, seems to improve glycemic response and insulin resistance compared to simple calorie restriction.
One question emerges clearly: the much vaunted scientific evidence is not so solid, at least not yet. For both alternate day fasting, 5:2 and Time Restricted Eating , the scientific evidence in humans seems very promising in some cases but still not conclusive. In all meta-analyses, the authors underline the need for trials conducted for longer periods (at least one year), according to well-defined and shared intervention protocols, and on certain categories of patients (normal weight or obese, prediabetic or healthy, men or women – because there seems to be an influence of sex in the response to fasting) in order to be able to draw truly indicative data.
Between meals and fasting: what happens
Although differently declined, intermittent fasting in its variants refers to a fundamental concept: to restore a lost metabolic balance. If on the one hand every living being is looking for food for survival, in the same way the body has evolved to adapt and make the most of unwanted periods of fasting, creating a natural alternation of anabolic phases, in which the organism , satiated and enriched with nutrients, it is dedicated to synthesis, cell growth and storage; and catabolic phases, where the lack of nutrients allows the body time to return to a basal state and pushes it to use the energy reserves set aside. If the lack of resources continues, the body responds and adapts: thus it activates defense mechanisms which make the cells more resistant to metabolic and oxidative stress, it slows down the metabolism, devotes itself more to repairing or removing damaged components, increases the quality control of the synthesis processes and triggers autophagy, i.e. a controlled cell death, an altruistic suicide, in which the components of old cells become available materials for new structures. Although it takes very little to interrupt this defense process, it is not clear however how many hours of fasting are needed to trigger it, if the 16 hours of the TRE are sufficient or if at least 24 hours of fasting are used every other day; also the metabolic switch, therefore the passage from glucose to fats, as a source of energy for the body, can vary, requiring from 12 to 36 hours of fasting to trigger.
But without disturbing autophagy, the problem also arises for the first catabolic phase: «A meal, especially if unbalanced and with a high energy content, represents a stressful event for the body, which must digest, absorb, control of glucose in the blood and storing the excess resources in fatty acids, processes that are accompanied by a typical postprandial inflammatory state» explains Mauro Serafini. “If the glycemic and lipid response of one meal resolves within a few hours, ingestion of a subsequent equally stressful meal, without an adequate interval of fasting time, lengthens the process, overloading the system. So on a day of continuous, high-calorie eating, we spend most of the 24 hours in a chronically inflamed, lipogenic postprandial state." The situation then worsens if the caloric load is taken in the evening (the later it is, the worse it is) when, in line with human circadian rhythms, insulin sensitivity decreases, worsening glycemia control and the inflammatory postprandial reaction increases, signals of a body preparing for rest and shelter. These results are in line with the data that has been demonstrating for some time now that the night shift , i.e. the reversal of daily activities between night and day, is associated with an increase in inflammation, risk factors for cardiovascular, metabolic and diabetes and a greater tendency towards obesity .
Buffering this situation is essential, but a form of intermittent fasting is not necessarily necessary, which by imposing the skipping of meals has more than one implication, both socially and psychologically. Strengthened by robust scientific evidence, physical exercise and a diet that does not exaggerate in calories, avoids constant snacking and is low in processed foods and rich in vegetables, unsaturated fats and complex whole carbohydrates, are able to maintain a beneficial state , even if every now and then it "goes wrong". This diet, aimed at reducing the post-prandial inflammatory response and respecting human circadian rhythms, is the heart of the dossier Immunonutrition, lifestyles and well-being , published last July by the 2003 Group for scientific research and whose fundamental concepts they are told to us by Mauro Serafini in the podcast dedicated to immuno- and chrononutrition.
However tempting such practices may seem, therefore, they may not prove to be as effective as we hope, especially in terms of general health, especially if we fast the wrong 16 hours (daytime) but in the remaining 8 we eat unbalanced or high-calorie meals. However, there is no doubt that with the obesity epidemic that today's society is facing and which seems to be on the rise, reducing body weight and improving the relative cardiovascular and metabolic parameters becomes a real necessity. The ways of science are endless, just get help from doctors or nutritionists to find your own.
(Excerpt from an article published in Science on the Net )
This is a machine translation from Italian language of a post published on Start Magazine at the URL https://www.startmag.it/sanita/digiuno-intermittente-si-grazie-anzi-no-parola-alla-scienza/ on Sat, 20 May 2023 05:20:11 +0000.