Inconsistencies exist with regard to influence of fasting and energy-restricting diets on markers of glucose and insulin controls. To address these controversial, this study was conducted to determine the impact of fasting diets on fasting blood sugars (FBSs), insulin, homeostatic model assessment insulin resistance (HOMA-IR) and hemoglobin A1c (HbA1c) levels. A comprehensive systematic search was carried out in electronic databases, i.e., Scopus, PubMed, and Web of Science through June 2019 for RCTs that investigated the impact of fasting and energy-restricting diets on circulating FBS, insulin, HOMA-IR and HbA1c levels from. Weighted mean difference (WMD) with the 95% CI were used for estimating combined effect size. The subgroup analysis was applied to specify the source of heterogeneity among articles. Pooled results from 30 eligible articles with 35 arms demonstrated a significant decrease in FBS (WMD): -3.376 mg/dl, 95% CI: -5.159, -1.594, p < 0.001), insulin (WMD: -1.288 muU/ml, 95% CI: -2.385, -0.191, p = 0.021), HOMA-IR (WMD: -0.41 mg/dl, 95% CI: -0.71, -0.10, p = 0.01) levels following fasting or energy-restricting diets. Nevertheless, no significant changes were observed in serum HbA1c levels. The subgroup analyses showed that overweight or obese people with energy restricting diets and treatment duration >8 weeks had a greater reduction in FBS, insulin and HOMA-IR level compared with other subgroups. The evidence from available studies suggests that the fasting or energy-restricting diets leads to significant reductions in FBS, insulin and HOMA-IR level and has modest, but, non-significant effects on HbA1c levels.