Impact of Intermittent Fasting vs. Continuous Calorie Restriction in Type 2 Diabetes Management: A Systematic Review

Background: Type 2 diabetes mellitus (T2DM) affects more than 830 million people globally as of 2022. Diet remains central to its management. Intermittent fasting (IF) and continuous calorie restriction (CCR) are two common strategies used to improve glycemic control. Their comparative effectiveness in real-world settings remains uncertain. Objective: To critically examine and compare the metabolic outcomes of IF and CCR in adults with T2DM, with attention to blood glucose, weight, insulin sensitivity, and adherence. Methods: This review followed PRISMA 2020 guidelines. We searched PubMed, Scopus, and the Cochrane Library through April 2025. Eligible studies included adults with T2DM who followed IF (alternate-day fasting, time-restricted feeding, or 5:2 diet) or CCR. Outcomes assessed were HbA1c, fasting glucose, body weight, and insulin resistance. We included only randomized controlled trials (RCTs) and systematic reviews with interventions lasting at least eight weeks. Risk of bias was evaluated using RoB 2 and AMSTAR 2. Results: Twelve studies met the inclusion criteria: eight systematic reviews, three RCTs, and one network meta-analysis. Both IF and CCR showed modest improvements in HbA1c (0.3%–1.2% reduction) and weight (2–6 kg loss). IF may offer better short-term glucose control and may be easier to follow in some cases. However, major limitations exist. Protocols varied widely, follow-up periods were short, and adherence was poorly tracked. Only one study had strong methodological quality. Conclusion: IF and CCR can both improve metabolic markers in T2DM. Current evidence is insufficient to recommend one approach over the other. The limited quality and consistency of existing research weaken the strength of the conclusions. Longer, high-quality studies are needed. Dietary plans should align with patient habits and clinical profiles.