ABSTRACT
Intermittent fasting is a dietary pattern that encompasses the 5:2 diet, alternate day fasting (ADF), and time restricted eating (TRE). All three involve alternating periods of fasting and ad libitum eating. Like other dietary strategies, intermittent fasting typically induces loss of both fat mass and lean mass. Exercise may thus be a useful adjuvant to promote lean mass retention while adding cardiometabolic, cognitive, mental, and emotional health improvements. In this narrative review, we summarize current evidence regarding the combination of intermittent fasting and exercise and its impacts on body weight, body composition, cardiometabolic risk, and muscular and cardiorespiratory fitness. A PubMed search was conducted to identify all trials lasting >4 weeks that combined 5:2, ADF, or TRE with any modality exercise and had body weight as an endpoint. A total of 23 trials (26 publications) were identified. Evidence suggests that combining intermittent fasting with exercise leads to decreased fat mass regardless of weight status. However, evidence is equivocal for the impact on other aspects of weight loss and body composition, fat free mass and cardiometabolic risk factors and may be dependent on weight status or exercise dosages (i.e., frequency, intensity, duration, and modality). Higher-powered trials are needed to determine the efficacy of combining exercise and intermittent fasting for benefits on bodyweight and cardiometabolic risk. Current evidence suggests that intermittent fasting does not impair adaptation to exercise training, and may improve explosive strength, endurance, and cardiopulmonary measures such as maximal oxygen consumption. Additionally, we discuss limitations in the current evidence base, and opportunities for continued investigation. Future trials in this area should consider interventions that have 1) increase sample size, 2) longer intervention duration, 3) broadened inclusion criteria, 4) objective measures of diet and exercise adherence, and 5) diversity of sample population.
