Effects of Intermittent Fasting and Carbohydrate-Restricted Diets on Insulin Resistance and Glycemic Control Markers: A Systematic Review and Meta-Analysis

Background: Intermittent fasting and carbohydrate-restricted dietary strategies have been investigated for improving insulin resistance and glycemic control, but interventions and study populations differ substantially. Objective: To summarize reported effects on fasting insulin, HOMAIR, fasting glucose, HbA1c, and the GH/IGF-1 axis in adults with excess weight or metabolic disorders. Methods: A systematic review of controlled dietary interventions was described using searches of PubMed, ScienceDirect, and Google Scholar for reports published from January 2016 to March 2026. Random-effects standardized mean differences (SMDs) were transcribed from the corresponding supplementary forest plots. Results: The available plots include eight estimates for insulin (SMD -0.79; 95% CI -1.03 to -0.56; I² 22.17%), seven for HOMA-IR (-0.84; -1.10 to -0.58; I² 26.21%), 13 for fasting glucose (-0.60; -0.84 to -0.35; I² 62.66%), and seven for HbA1c (-0.81; -1.17 to -0.44; I² 64.15%). Only one study supplied GH/IGF-1 findings. The source PRISMA diagram and descriptive study table disagree on the number of included entries, preventing confirmation of a unique participant total from the supplied documents. Conclusions: The reported summaries favor lower markers of insulin resistance and glycemic exposure during the evaluated dietary interventions. Their clinical interpretation is limited by mixed protocols, incomplete outcome reporting, uncertainty about the precise within-study contrasts, and the absence of a documented study-level risk-of-bias evaluation.