Introduction
Intermittent energy restriction (IER) diets, including alternate day fasting (ADF), time-restricted eating (TRE), and the 5:2 diet, are dietary approaches to lose body weight. The superior effects of IER compared to continuous energy restriction (CER) diets are however controversial. Therefore, this systematic review and meta-analysis compared the effects of IER to CER on changes in body weight and composition.

Methods:
A systematic search was performed in Embase, PubMed, and Cochrane in February 2022 to identify articles that compared side-by-side the effects of IER diets - ADF, TRE or the 5:2 diet - to CER diets in healthy adults. Outcomes included body weight, body mass index (BMI), fat and fat-free mass, and waist circumference (WC).

Results
Twenty-three studies were included. No overall significant differences were reported between IER and CER for changes in body weight, BMI, and fat and fat-free mass (p>0.05). WC was more reduced in IER compared to CER (weighted mean difference (WMD): -1.24 cm, 95% CI: -2.08 to -0.40, p=0.004). Effects of the three different IER diets were comparable to CER, except for changes in BMI and WC in the 5:2 diet. The between-group decrease in energy intake during the intervention period within studies was comparable for eleven studies, different for five studies, and not reported for four studies. After excluding studies that did not report energy intake, weight loss was greater in IER compared to CER, but no differences were observed between subgroups in which the reduction in energy intake was comparable (WMD: -0.82 kg, 95% CI: -1.31 to -0.32, p=0.001) or different (WMD: -1.07 kg, 95% CI: -1.89 to -0.26, p=0.009).

Conclusion
Reductions in body weight and composition were comparable between the diets. The results should be interpreted with caution, as differences in energy intake between the dietary regimens may have influenced the overall findings