WHAT STUDIES SAY ABOUT INTERMITTENT FASTING Fasting (voluntary periods of abstinence from food and liquids) is an ancient practice, found in many religious practices. In recent years, a secular adaptation, that of intermittent fasting / IF / time restricted feeding, has become increasingly popular, being associated in the media with increasing longevity, weight loss, efficiency in cancer, diabetes, diseases cardiovascular and other chronic diseases.
In parallel with the public interest, the number of scientific articles on this subject is constantly increasing. However, human experimental studies are few at this time, also having a small number of participants. Most information on the potential benefits of intermittent fasting is based on animal studies (performed on male rats). Human studies have generally been limited to observational studies of different religious customs, such as Ramadan, cross-sectional studies of eating habits, and experimental studies with a small number of participants.
In this ebook, we will analyze the current evidence on the effects of IF, from the molecular level to the clinical results.
Human metabolism: the post-feeding cycle In order to understand the differences between the approaches in the IF position and the mechanisms of the clinical effects it is necessary to know the main actors of the energy metabolism and how they change during the periods of fasting.
Glucose is the main energy source for most tissues. Fatty acids (AG) are an alternative source used during fasting. To explain their dynamics, Randel proposed in 1963 a theory of energy metabolism in which glucose and fatty acids compete for oxidation ("burns" for energy). The fast-food cycle goes through 4 stages depending on the time elapsed since the last meal. These are the stage:
Feeding (0-3h) Food digestion causes an increase in blood sugar, which results in an increase in insulin
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Insulin inhibits lipolysis (fat degradation) Glucose is used as an energy source, the excess is stored either as glycogen, until it reaches storage capacity in this form, or as AGs stored in adipose tissue. Post-absorption / early post (3-18h) A decrease in glucose causes a decrease in insulinemia Glycogen deposits are used and glucose is synthesized from other sources through the process of gluconeogenesis. Lipolysis begins, thus increasing the level of AG From post (18-48h) Insulin continues to drop Metabolic shift: The main energy sources used are AG and their derivatives, the ketone bodies Lipolysis increases the concentration of AGL (free fatty acids) Catabolism of muscle proteins Increases the release of glucagon and corticosteroids (hormones that increase blood sugar) Long-term job (over 48h) Insulin continues to drop The levels of ketone bodies increase Catabolism of certain amino acids is inhibited to save proteins Glucose oxidation in muscles is inhibited
What is intermittent fasting? IF represents the drastic or total limitation of the caloric intake in a certain period of time. There are many variants depending on the number of calories allowed, the duration of the job and the type of alternation of the periods of work with those of feeding. The various IF regimes can be divided into three classes:
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Alternate day fasting - alternating the days of fasting (caloric intake of maximum 25% of the required) with those of normal feeding: example 5/2 program - 5 days of unrestricted feeding and 2 days of fasting Time restricted fasting - limiting the power window to several hours per day (common windows / food: 6/18, 8/16) Fasting periodically - fasted up to 24 hours, 1-2 times a week, unrestricted food for the rest of the days Thus, the limitation of the supply window includes the first two phases of the feeding-post cycle, and the other two variants of IF, the first three phases.
Is IF an effective method of weight loss? An effective nutritional intervention for weight loss is one that promotes long-term adherence and positively influences metabolic markers. In general, such interventions maintain satiety, respect the minimum nutritional needs, determine a maximum decrease of adipose tissue with the preservation of muscle mass, are easy to administer and monitor.
But intermittent fasting is much more effective at helping you lose weight than calorie deficiency. If you want to find out more about it, read the article Intermittent Fasting vs. Eating Less – Which One is Better?
The circadian rhythm The functioning of organisms is cyclical. Internal mechanisms work so that physiological processes take place at optimal times .In humans, the suprachiasmatic nucleus of the hypothalamus is the "central clock", being sensitive to light stimuli. However, it also receives information from peripheral structures such as the liver ("clock" sensitive to food intake). Thus, the time of day influences energy metabolism, hormonal secretion, physical coordination, coordination capacity and many other physiological processes.
Changes in normal circadian rhythm have been associated with a number of disorders such as increased insulin resistance, prevalence of cardiovascular disease and cancer.
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Fasting variants that dramatically reduce or exclude energy intake during the evening and night could help resynchronize the circadian rhythm. This resynchronization is a proposed mechanism for reprogramming energy metabolism and improving body weight control. Studies in mice have shown a positive effect of the same type of intervention (feeding animals only at night, these being nocturnal) on the microbiome. Disorders of intestinal flora have been associated with multiple pathologies and problems with maintaining normal body weight.
Another important element influenced by the circadian rhythm is sleep .Multiple observational studies have linked late meals with reduced sleep duration and quality.
Immunity Calorie restriction regimens and IF protocols have been associated with positive effects in the prevention, but not the treatment of autoimmune diseases such as multiple sclerosis, autoimmune diabetes or rheumatoid arthritis .A potential mechanism of IF is the destruction of abnormal cells during fasting, followed by regeneration of the affected tissues during the refueling period.
Multiple studies are currently underway in which IF is used to increase the efficacy and decrease the adverse reactions of chemotherapies .The types of cancer, tumor stage and chemotherapies with which the addition of IF would have the greatest effect are not yet known, most of the studies completed being in animal models.
So what do IF studies say? Studies in laboratory animals such as rats support the hypothesis that intermittent fasting, in keeping with the normal dietary window, improves metabolic profile and reduces the risk of obesity and chronic diseases such as diabetes and cancer. However, data from human studies are limited. They suggest that intermittent fasting is not physically or mentally harmful to healthy adults, with normal or above normal body weight .In other categories of people, this regimen may have side effects (for example, type 2 diabetics increase the risk of hypoglycemic episodes).
Intermittent fasting is just as effective as other weight loss methods studied, when comparing interventions that cause a similar caloric deficit. Because the success of losing weight and maintaining
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the new weight is closely linked to long-term adherence, there is a subgroup of people who will have better results using this approach.
The effects of intermittent fasting on sleep, physical activity or clinical outcomes such as diabetes, cardiovascular disease, cancer or other chronic diseases, are still being studied, the current data being insufficient.
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