Type 2 diabetes mellitus (T2DM) is a chronic disease increasing in global prevalence. While habitual consumption of walnuts is associated with reduced risk of cardiovascular disease, there is inconsistent evidence for the impact of walnut consumption on markers of glycaemic control. This systematic review and meta-analysis aimed to examine the effect of walnut consumption on markers of blood glucose control. A systematic search of Medline, PubMed, CINAHL and Cochrane databases (to 2nd March 2019) was conducted. Inclusion criteria were randomised controlled trials conducted with adults which assessed the effect of walnut consumption on: fasting blood glucose and insulin, glycated haemoglobin, and Homeostatic Model Assessment of Insulin Resistance. Random effects meta-analyses were conducted to assess the weighted mean differences (WMD) for each outcome. Risk of bias in studies was assessed using the Cochrane Risk of Bias tool 2.0. Sixteen studies providing 18 effect sizes were included in the review. Consumption of walnuts did not result in significant changes in fasting blood glucose levels (WMD: 0.331 mg/dL [95% confidence intervals: -0.817, 1.479]) or other outcome measures. Studies were determined to have either 'some concerns' or be at 'high risk' of bias. There was no evidence of an effect of walnut consumption on markers of blood glucose control. These findings suggest that the known favourable effects of walnut intake on cardiovascular disease are not mediated via improvements in glycaemic control. Given the high risk of bias observed in the current evidence base, there is a need for further high quality randomised controlled trials.
Available for download on Wednesday, April 21, 2021