The influence of fasting and energy restricting diets on IGF-1 levels in humans: A systematic review and meta-analysis

Abstract

Background: Fasting and energy restricting diets have a potential means of delaying or preventing the onset of a range of age-related metabolic and neoplastic diseases. Consistently at the centre of this effect appears to be a significant reduction in circulating IGF-1 levels. The aim of the current systematic review and meta-analysis was to determine the influence of fasting and energy restriction on IGF-1 levels in human subjects. Methods: A comprehensive systematic search was conducted from onset of the database to February 2019 in Embase, MEDLINE/PubMed, and SCOPUS to identify randomized clinical trials that investigating the impact of fasting or energy restriction circulating IGF-1 levels. Effect size was reported as weighted mean difference (WMD) and 95% confidence intervals (CI) using a random-effects models. Subgroup analysis was performed to identify the probable source of heterogeneity among trials. Results: Total pooling of fasting and energy restriction randomised controlled trials in WMD analysis revealed no significant effect on circulating IGF-1 levels (WMD: −16.41 ng/ml, 95% CI: −35.88, 3.07). Sub grouped analysis fasting regimens appeared to substantially reduce IGF-1 (WMD: -28.87 ng/ml, 95% CI: −43.69, −14.05, I2=00%), energy restricting regimens failed to do the same (WMD: -10.98 ng/ml, 95% CI: −33.08, 11.11, I2=90%). Within this final subgrouping, it was observed that only energy restriction regimens of 50% or greater of normal daily energy intake were capable of significantly reducing IGF-1 levels (WMD: -36.57 ng/ml, 95% CI: −59.19, −13.95, I2=00%). Finally, a meta regression were noted in which the percentage restriction of daily energy intake inversely correlated with plasma IGF-1 levels (p=0.04). Conclusion: This study uncovered that fasting significantly reduced levels of IGF-1, while energy restriction diets were successful only when intake was reduced by 50% or more.