The effects of intermittent energy restriction on metabolic and cardiovascular function and overall health

A novel model of dietary intervention is attracting increasing scientific attention. This is intermittent energy restriction (IER), which is based on the intermittent restriction of caloric intake, with shifts between periods of reduced caloric intake and periods of unrestricted ad libitum feeding. The most carefully studied regimens of IER are those of energy restriction on two consecutive days per week, alternate day energy restriction by 60-70%, and complete fasting on alternate days (intermittent fasting, IF). This is a review of the evidence to date, critically highlighting the lack of high-quality scientific data to demonstrate the superior or equal long-term safety and efficacy of intermittent dietary regimens compared with continuous hypocaloric diets. The few available randomized studies comparing intermittent dietary regimens with continuous hypocaloric diets in overweight and obese patients, report equal efficacy in terms of weight loss for a period of up to 6 months. To date, no studies suggest that intermittent diets are able to prevent weight gain in normal-weight subjects. The data concerning the impact of intermittent diets on ectopic fat stores, adipocyte size, fat-free mass, insulin resistance and metabolic flexibility, are heterogeneous. Some studies in normal-weight subjects have shown detrimental effects of intermittent diets on fat distribution and metabolic homeostasis, raising safety concerns and the need for further investigation. In view of the knowledge gaps highlighted in this review, the popularity of various intermittent diets underscores the vital need for rigorous research in the field of intermittent dieting, with appropriately designed, long-term, randomized studies in several subgroups of patients.