Physiological and Biochemical Effects of Intermittent Fasting on Insulin Sensitivity and Glucose Metabolism: A Systematic Review

OBJECTIVES This study aimed to review the physiological and biochemical effects of intermittent fasting on insulin sensitivity and glucose metabolism in human studies published between 2019 and 2025. METHODOLOGY A literature search was conducted in electronic databases, such as PubMed, Google Scholar, ScienceDirect, SpringerLink, Wiley Online Library and Cochrane Library, for original human studies from January 2019 to December 2025. The studies included in the analysis were randomised controlled trials, randomised clinical trials, open-label randomised trials, randomised crossover trials and prospective interventional trials of intermittent fasting or time-restricted eating. There were no reviews, meta-analyses, narrative articles, case reports, animal or in vitro studies, nor pilot studies. The following data were collected for study characteristics, insulin sensitivity, glucose metabolism, physiological outcomes, biochemical markers, and risk of bias. RESULTSTwenty-one original studies were included. Most studies reported favourable effects of intermittent fasting on glucose regulation, fasting insulin, HOMA-IR, HbA1c, continuous glucose monitoring outcomes, body weight, waist circumference, lipid profile, and cardiometabolic markers. Benefits were more consistent among adults with obesity, metabolic syndrome, type 2 diabetes, polycystic ovary syndrome, and increased diabetes risk. Early time-restricted eating and 8–10-hour eating windows showed more promising metabolic effects than less structured fasting patterns. However, the magnitude of benefit varied across studies. CONCLUSION Intermittent fasting may improve insulin sensitivity, glucose metabolism, and related physiological and biochemical outcomes, especially in metabolically high-risk adults. However, heterogeneity in fasting schedules, intervention duration, population characteristics, and outcome measures limits direct comparison. Larger long-term randomised trials are needed to identify the safest and most effective fasting protocols.