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

Findings on the effect of walnut consumption on cardio metabolic profiles in individuals with abnormal glucose homeostasis are conflicting. We summarized 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. Randomized trials that enrolled individuals with abnormal glucose homeostasis in which the main intervention was walnut consumption were included. Abnormal glucose homeostasis 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 weight [WMD: -0.13; 95% CI: -0.64, 0.39 kg], BMI [-0.08; -0.47, 0.32 kg/m2] and waist circumference [0.01; -0.50, 0.52 cm] was observed. Although walnut intake did not influence on lipid profiles (including triglyceride, 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; -0.20, 0.01 mmol/L; P=0.06]. Other cardio-metabolic factors including markers of glycemic control [fasting blood glucose and hemoglobin A1C 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 [0.93%;: 0.16, 1.71%]. Summarizing earlier evidence, we found that walnut consumption might influence FMD and LDL-cholesterol levels in individuals with abnormal glucose homeostasis. It did not affect other cardio-metabolic profiles in these individuals.