Benefits of Short-Term (4-Week) Daily Walnut Consumption in Middle-Aged Adults at Risk for Metabolic Syndrome: Outcomes of a Randomized Controlled Trial

<b>Background:</b> Epidemiological research has shown that regular walnut (from <i>Juglans regia</i> L.) consumption is associated with a reduced risk of cardiovascular disease (CVD), potentially attributable to their antioxidant and anti-inflammatory properties. The vascular cellular adhesion molecule-1 (VCAM-1), a protein upregulated in CVD, has been previously examined in relation to walnut consumption. However, the clinical findings regarding the effects of walnuts on endothelial function among middle-aged individuals susceptible to metabolic syndrome (MetS) remain inconclusive. <b>Objective:</b> This study examined the effects of daily walnut consumption over a four-week period on cardiometabolic parameters (lipid and glycemic profiles, as well as soluble VCAM-1 levels) and anthropometric measurements in middle-aged individuals with at least one altered MetS parameter and no medication. <b>Methods:</b> In a randomized controlled cross-over trial, 22 eligible Caucasian participants (48.81 ± 4.3 years) were selected and randomly assigned to receive either 45 g of walnuts per day or no walnuts within a controlled diet. There were two 28-day intervention periods, with a one-month washout period in between. Clinical and biochemical evaluations were conducted at the beginning and end of each intervention period. <b>Results:</b> A total of 20 participants completed the intervention and were analyzed, with walnuts being well tolerated. A significant decrease in waist circumference (<i>p</i> = 0.049) and a slight change in fasting blood glucose (<i>p</i> = 0.089) were noted following walnut intake. <b>Conclusions:</b> Short-term (4 weeks) dietary supplementation with walnuts resulted in a statistically significant reduction in waist circumference while not impacting the overall health status of participants. Longer-term studies are necessary to investigate the benefits of daily walnut consumption and its impact on the onset and development of MetS in this age group.