Context: The effectiveness of intermittent energy restriction (IER) and periodic fasting (PF) in the management of type 2 diabetes (T2D) remains a subject of discussion.

Objective: The aim of this systematic review is to summarize current knowledge of the effects of IER and PF in patients with T2D on markers of metabolic control and the need for glucose-lowering medication.

Data sources: PubMed, Embase, Emcare, Web of Science, Cochrane Library, CENTRAL, Academic Search Premier, Science Direct, Google Scholar, Wiley Online Library, and LWW Health Library were searched for eligible articles on March 20, 2018 (last update performed November 11, 2022). Studies that evaluated the effects of IER or PF diets in adult patients with T2D were included.

Data extraction: This systematic review is reported according to PRISMA guidelines. Risk of bias was assessed through the Cochrane risk of bias tool. The search identified 692 unique records. Thirteen original studies were included.

Data analysis: A qualitative synthesis of the results was constructed because the studies differed widely in terms of dietary interventions, study design, and study duration. Glycated hemoglobin (HbA1c) declined in response to IER or PF in 5 of 10 studies, and fasting glucose declined in 5 of 7 studies. In 4 studies, the dosage of glucose-lowering medication could be reduced during IER or PF. Two studies evaluated long-term effects (≥1 year after ending the intervention). The benefits to HbA1c or fasting glucose were generally not sustained over the long term. There are a limited number of studies on IER and PF interventions in patients with T2D. Most were judged to have at least some risk of bias.

Conclusion: The results of this systematic review suggest that IER and PF can improve glucose regulation in patients with T2D, at least in the short term. Moreover, these diets may allow for dosage reduction of glucose-lowering medication.

Systematic review registration: PROSPERO registration no. CRD42018104627.