Effects of Intermittent Fasting on Cardiometabolic Health: An Energy Metabolism Perspective

Abstract

This review summarizes the effects of different types of intermittent fasting (IF) on human cardiometabolic health, with a focus on energy metabolism. First, we discuss the coordinated metabolic adaptations (energy expenditure, hormonal changes and macronutrient oxidation) occurring during a 72 h fast. We then discuss studies investigating the effects of IF on cardiometabolic health, energy expenditure and substrate oxidation. Finally, we discuss how IF may be optimized by combining it with exercise. In general, IF regimens improve body composition, ectopic fat, and classic cardiometabolic risk factors, as compared to unrestricted eating, especially in metabolically unhealthy participants. However, it is still unclear whether IF provides additional cardiometabolic benefits as compared to continuous daily caloric restriction (CR). Most studies found no additional benefits, yet some preliminary data suggest that IF regimens may provide cardiometabolic benefits in the absence of weight loss. Finally, although IF and continuous daily CR appear to induce similar changes in energy expenditure, IF regimens may differentially affect substrate oxidation, increasing protein and fat oxidation. Future tightly controlled studies are needed to unravel the underlying mechanisms of IF and its role in cardiometabolic health and energy metabolism.

Keywords: 5:2 diet; Ramadan; alternate-day fasting; cardiovascular health; energy expenditure; exercise; fasting-mimicking diet; fat oxidation; metabolic rate; modified periodic fasting; time-restricted eating; twice-weekly fasting.

Figure 1

Different types of intermittent fasting. The green and red shading within the battery symbols illustrate the energy intake during the eating and fasting periods, with one battery symbol representing 100% of energy needs. The alternative-day modified fasting, twice-weekly fasting, and modified periodic fasting approaches do not typically restrict food intake to a specific time during the fasting days; therefore, the reduced food intake during these days can be consumed within a single meal (darker blue areas) or various meals (lighter blue areas). The blue areas within the circles indicate the eating window. The areas shaded in red in the calendar tables indicate fasting periods, while the green areas indicate eating periods. * Fast days in the twice-weekly fasting may be consecutive or not.

Figure 2

Dynamic changes of blood energy substrates (Panel (A)) and blood hormones (Panel (B)) during a 72 h fasting period after consuming a meal following an overnight fast.

Figure 3

Dynamic changes of whole-body substrate utilization (Panel (A)) and metabolic provenance of energy (Panel (B)) during a 72-h fasting period after consuming a meal following an overnight fast.