Effects of Intermittent Energy Restriction Compared with Those of Continuous Energy Restriction on Body Composition and Cardiometabolic Risk Markers – A Systematic Review and Meta-Analysis of Randomized Controlled Trials in Adults

The interest in intermittent energy restriction (IER) diets as weight loss approach is increasing. Different IER protocols exist, including time-restricted eating (TRE), alternate-day fasting (ADF), and the 5:2 diet. This meta-analysis compared the effects of these IER diets to continuous energy restriction (CER) on anthropometrics and cardiometabolic risk markers in healthy adults. Twenty-eight trials were identified that studied TRE (k=7), ADF (k=10), or the 5:2 diet (k=11) for 2 to 52 weeks. Energy intakes between intervention groups within a study were comparable (17 trials), lower in IER (5 trials) or not reported (6 trials). Weighted mean differences (WMD) were calculated using fixed- or random-effects models. Changes in body weight (WMD: -0.42 kg; 95% CI: -0.96 to 0.13; p=0.132) and fat mass (WMD: -0.31 kg; 95% CI: -0.98 to 0.36; p=0.362) were comparable when results of the three IER diets were combined and compared to those of CER. All IER diets combined reduced fat free mass (WMD: -0.20 kg; 95% CI: -0.39 to -0.01; p=0.044) and waist circumference (WMD: -0.91 cm; 95% CI: -1.76 to -0.06; p=0.036) more than CER. Effects on body mass index (BMI), glucose, insulin, homeostatic model assessment for insulin resistance (HOMA-IR), serum lipids and lipoproteins, and blood pressure did not differ. Further, TRE reduced body weight, fat mass, and fat mass more than CER, while ADF improved HOMA-IR more. BMI reduced less in the 5:2 diet compared to CER. In conclusion, the three IER diets combined did not lead to superior improvements in anthropometrics and cardiometabolic risk markers compared to CER diets. Slightly greater reductions were however observed in fat free mass and waist circumference. To what extent differences in energy intakes between groups within studies may have influenced these outcomes should be addressed in future studies. This meta-analysis was registered at PROSPERO as CRD42022350008.