Effect of Intermittent Fasting on Weight Loss in Overweight and Obese Adults: A Systematic Review of Clinical Trials

Intermittent fasting (IF), an alternative calorie restriction strategy, supports weight management and may enhance cardiovascular health, improve glycemic control, and offer potential protective effects against cancer, alongside other possible health benefits. The objective of this systematic review is to study the impact of intermittent fasting on weight loss among overweight and obese adults. The original research articles were searched in four electronic databases: PubMed, Cochrane Library, Google Scholar, and ScienceDirect, with specific time frame restrictions. After going through an organized process of screening and eligibility, 26 out of 2307 studies fitting the inclusion criteria were identified. The established methodological procedure observed in this review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines to ensure transparency and credibility in the approach. All the included studies demonstrated statistically significant reductions in body weight resulting from intermittent fasting interventions over durations ranging from 3 to 50 weeks. However, several trials exhibited comparable effectiveness between intermittent fasting and continuous calorie restriction. The findings suggest that intermittent fasting is an effective approach for weight loss, contributing to favorable changes in body composition, including a decrease in fat mass, an improvement in lean mass, and a reduction in waist circumference. These outcomes collectively contribute to improvements in body mass index (BMI) and overall metabolic health. The risk of bias was assessed using the Cochrane Risk of Bias 2.0 (RoB2) tool for 24 RCT studies, resulting in 16 studies with a low risk of bias, 1 study with a high risk, and 7 studies showing a moderate risk. While two included non-randomized controlled studies were assessed using the MMAT tool. Different forms of intermittent fasting including TRE (16:8, 20:4, 14:10, and 18:6), Alternate Day Fasting (ADF), and IF (5:2) appear promising for sustainable weight management. Among these, ADF and TRE (particularly 16:8 protocols) demonstrated the most consistent evidence of weight reduction across included studies, with no evidence of statistically significant differences in comparison with continuous calorie restriction. Moreover, future studies should compare different protocols, such as time-restricted eating and alternate-day fasting, while exploring underlying physiological mechanisms to guide healthcare professionals in creating effective, personalized dietary strategies for managing overweight and obesity.