The effect of walnut consumption on cardiometabolic profiles of individuals with abnormal glucose homoeostasis: a systematic review and meta-analysis of clinical trials.

Findings on the effect of walnut consumption on cardiometabolic profiles in individuals with abnormal glucose homoeostasis are conflicting. We summarised earlier data in this regard. A systematic literature search of relevant reports published in Medline/PubMed, ISI web of Science, EMBASE, SCOPUS and Google Scholar up to October 2020 was conducted. Randomised trials that enrolled individuals with abnormal glucose homoeostasis in which the main intervention was walnut consumption were included. Abnormal glucose homoeostasis was defined as a spectrum of impaired glucose tolerance or pre-diabetic status that is associated with insulin resistance. Twelve studies were included in systematic review and eight in meta-analysis. No significant effect of walnut consumption on anthropometric measures, including weighted mean difference (WMD: -0·13; 95 % CI -0·64, 0·39 kg), BMI (-0·08; 95 % CI -0·47, 0·32 kg/m) and waist circumference (0·01; 95 % CI -0·50, 0·52 cm) was observed. Although walnut intake did not influence on lipid profiles (including TAG, total- and HDL-cholesterol levels), individuals in the intervention group tended to have lower levels of LDL-cholesterol than those in the control group (-0·10; 95 % CI -0·20, 0·01 mmol/l; = 0·06). Other cardiometabolic factors including markers of glycaemic control (fasting blood glucose and HbA1C levels), blood pressure and stimulus-adjusted response measure (a parameter of endothelial function) were not significantly affected. However, walnut consumption resulted in a significant increase in flow-mediated dilation (FMD) (0·93 %; 95 % CI 0·16, 1·71 %). Summarising earlier evidence, we found that walnut consumption might influence FMD and LDL-cholesterol levels in individuals with abnormal glucose homoeostasis. It did not affect other cardiometabolic profiles in these individuals.