Effect of the Mediterranean diet on glycated haemoglobin A1c levels in adults with type 2 diabetes: A Systematic Review

Abstract

Background: Type 2 diabetes is a chronic disease with an increasing prevalence worldwide. The Mediterranean diet has become well known owing to its possible health benefits. The aim of this systematic review was to investigate the effect of the Mediterranean diet on glycated haemoglobin A1c (HbA1c) levels in adults with type 2 diabetes. Methods: Two databases (Web of Science and PubMed) were systematically searched for relevant studies without language restriction. The search was performed from July to August 2021. The inclusion criteria were studies published between 2010 and 2021 that assessed the effect of the Mediterranean diet on HbA1c levels in adults aged >18 years with type 2 diabetes. The Cochrane tool was used to assess the risk of bias. Results: Of 155 studies identified, seven met the inclusion criteria, of which four were randomised controlled trials (RCTs), two were cross-sectional studies, and one was a descriptive observational study. Three of the RCTs reported a significant reduction in HbA1c level in the Mediterranean diet group compared with the control group, whereas one RCT reported a marked reduction in HbA1c level, but the effect diminished over 2 years. In observational studies, higher adherence to the Mediterranean diet was found to be associated with reduced HbA1c levels. Conclusion: The results suggest that the Mediterranean diet had a favourable effect on the HbA1c levels of the patients with type 2 diabetes in this study. Owing to the limited number of included studies, more intervention trials are warranted to examine the long-term effect of the Mediterranean diet.