The influence of fasting and energy-restricted diets on leptin and adiponectin levels in humans: A systematic review and meta-analysis

Background & aims: Fasting and energy-restricted diets have been evaluated in several studies as a means of improving cardiometabolic biomarkers related to body fat loss. However, further investigation is required to understand potential alterations of leptin and adiponectin concentrations. Thus, we performed a systematic review and meta-analysis to derive a more precise estimate of the influence of fasting and energy-restricted diets on leptin and adiponectin levels in humans, as well as to detect potential sources of heterogeneity in the available literature. Methods: A comprehensive systematic search was performed in Web of Science, PubMed/MEDLINE, Cochrane, SCOPUS and Embase from inception until June 2019. All clinical trials investigating the effects of fasting and energy-restricted diets on leptin and adiponectin in adults were included. Results: Twelve studies containing 17 arms and a total of 495 individuals (intervention = 249, control = 246) reported changes in serum leptin concentrations, and 10 studies containing 12 arms with a total of 438 individuals (intervention = 222, control = 216) reported changes in serum adiponectin concentrations. The combined effect sizes suggested a significant effect of fasting and energy-restricted diets on leptin concentrations (WMD: ?3.690 ng/ml, 95% CI: ?5.190, ?2.190, p ? 0.001; I2 = 84.9%). However, no significant effect of fasting and energy-restricted diets on adiponectin concentrations was found (WMD: ?159.520 ng/ml, 95% CI: ?689.491, 370.451, p = 0.555; I2 = 74.2%). Stratified analyses showed that energy-restricted regimens significantly increased adiponectin (WMD: 554.129 ng/ml, 95% CI: 150.295, 957.964; I2 = 0.0%). In addition, subsequent subgroup analyses revealed that energy restriction, to ?50% normal required daily energy intake, resulted in significantly reduced concentrations of leptin (WMD: ?4.199 ng/ml, 95% CI: ?7.279, ?1.118; I2 = 83.9%) and significantly increased concentrations of adiponectin (WMD: 524.04 ng/ml, 95% CI: 115.618, 932.469: I2 = 0.0%). Conclusion: Fasting and energy-restricted diets elicit significant reductions in serum leptin concentrations. Increases in adiponectin may also be observed when energy intake is ?50% of normal requirements, although limited data preclude definitive conclusions on this point. 2020 Elsevier Ltd and European Society for Clinical Nutrition and MetabolismThis work was supported financially by the National Nutrition and Food Technology Research Institute , Shahid Beheshti University of Medical Sciences , Tehran, Iran (Grant Number: 1000328 ).Scopu