Although nut consumption has consistently been linked to a lower risk of cardiovascular diseases, its effect on endothelial function, “a prognostic marker” of cardiovascular disease (CVD), is less clear.
Endothelial dysfunction is an event in the early-stage of atherosclerosis and an independent predictor of future CVD events.
As such, 10 randomised controlled trials (RCTs), using flow-mediated dilation (FMD) as a measurement of endothelial function, were assessed to determine the effects of nuts in adults aged 18 and above.
Walnuts in particular were said to have a “beneficial effect”, significantly enhancing FMD unlike other types of nuts.
"This might be explained by the small number of trials which used other nuts in the intervention," wrote scientists from China and Hong Kong. "Among 10 trials, six were conducted with walnuts, whereas one each with almonds and hazelnuts and two with pistachios. Another explanation may be due to the different nutrient profiles of walnuts than other nuts."
While nuts in general are rich in monounsaturated and polyunsaturated fatty acids, “walnuts contain greater amounts of plant n-3 fatty acid ALA”, which could increase the membrane fluidity of endothelial cells and reduce endothelial inflammation.
Though blood pressure and lipid profile are known to be traditional risk factors in cardiovascular diseases, endothelial dysfunction “has also been found as a marker of susceptibility to future cardiovascular events”, and these risk factors have been shown to interact. LDL cholesterol is a direct cause of endothelial dysfunction, and nuts — especially walnuts — can help to mitigate these factors.
Furthermore, walnuts are rich in α-tocopherol and γ-tocopherol, which are strong antioxidants that lessen the severity of atherosclerosis.
The study concluded that “walnut consumption may improve endothelial function measured by FMD."
It added that "more studies examining the effect of nuts other than walnuts on FMD are needed” and that “large-scale randomised trials with a longer duration are warranted."
Source: Clinical Nutrition
“Effect of nut consumption on vascular endothelial function: A systematic review and meta-analysis of randomized controlled trials”
Authors: Yunjun Xiao, et al.