A scoping review of intermittent fasting, chronobiology, and metabolism

Abstract

Intermittent fasting (IF) has emerged as a flexible strategy whereby both delayed and early eating windows have shown clinical benefits-with several IF protocols improving glycemic and lipid profiles, as well as inducing weight loss-although early eating windows are better aligned with circadian rhythms. As discussed in this review, however, IF does not appear to be more effective than traditional diets at the group level and its effects largely depend on energy restriction. As such, health professionals can consider IF programs a potential route at the individual level but, based on the current evidence, need not advocate these programs for the population at large. Chronobiology plays a crucial role in modulating many physiologic systems in which there is nutritional synergism with meal timing. Given that intermittent fasting (IF) has grown as a flexible dietary method consisting of delayed or early eating windows, this scoping review addresses the effects of IF protocols on metabolism as they relate to clinical nutrition and the circadian system. Although nocturnal habits are associated with circadian misalignments and impaired cardiometabolic profile-and nutritional physiology is better orchestrated during the day-most findings are based on animal experiments or human studies with observational designs or acute meal tests. Well-controlled randomized clinical trials employing IF protocols of delayed or early eating windows have sometimes demonstrated clinical benefits, such as improved glycemic and lipid profiles, as well as weight loss. However, IF does not appear to be more effective than traditional diets at the group level, and its effects largely depend on energy restriction. Thus, efforts must be made to identify patient biological rhythms, preferences, routines, and medical conditions before individual dietary prescription in clinical practice.