Key Findings:
West and co-workers have reported that diets high in ALA from walnuts and flaxseed oil significantly reduce C-reactive protein (CRP) and several markers of inflammation and endothelial dysfunction in adults with high cholesterol. This study is the first to show significant reductions in systemic vascular resistance with diets high in both omega-3 and omega-6 fatty acids. In healthy adults with elevated LDL-cholesterol, an LA diet (which contained walnuts and walnut oil, but no flax oil) significantly reduced blood pressure and vascular resistance, both at rest and during acute stress. Adding more ALA from flax resulted in reductions in CRP and increases in flow mediated dilation (FMD). The degree of changes were correlated which suggests that improvement in vascular endothelial function may result from the anti-inflammatory effects of ALA. On the LA diet only, there was an inverse correlation between change in serum EPA (C20:5 n3) and change in systolic blood pressure. Changes in serum ALA and the LA-ALA ratio were not significantly correlated with vascular or blood pressure responses to the diets. The authors note that the anti-inflammatory effects of ALA may not be solely due to conversion to long chain omega-3 fatty acids. Significant reductions in systemic vascular resistance were noted with ALA suggesting an acute beneficial effect on endothelial function. Subjects with larger increases in serum concentrations of PUFA exhibited larger decreases in diastolic blood pressure. Improvements in endothelial function and cardiovascular responses to stress would be expected to significantly reduce the risk of CVD.
ABSTRACT:
Polyunsaturated fatty acids (PUFA) have beneficial effects on cardiovascular risk, although the mechanisms are incompletely understood. In a previous article, we showed significant reductions in low density lipoprotein cholesterol and several markers of inflammation with increasing intake of alpha-linolenic acid (ALA) from walnuts and flax. To examine effects of ALA on cardiovascular responses to acute stress, flow-mediated dilation (FMD) of the brachial artery, and blood concentrations of endothelin-1 and arginine-vasopressin (AVP). Using a randomized, crossover study design, cardiovascular responses to acute stress were assessed in 20 hypercholesterolemic subjects, a subset of whom also underwent FMD testing (n =12). Participants were fed an average American diet (AAD) and 2 experimental diets that varied in the amount of ALA and linoleic acid (LA) that they contained. The AAD provided 8.7% energy from PUFA (7.7% LA, 0.8% ALA). On the LA diet, saturated fat was reduced, and PUFA from walnuts and walnut oil provided 16.4% of energy (12.6% LA, 3.6% ALA). On the ALA diet, walnuts, walnut oil, and flax oil provided 17% energy from PUFA (10.5% LA, 6.5% ALA).The ALA and LA diets significantly reduced diastolic blood pressure (22 to 23 mm Hg) and total peripheral resistance ( -24%), and this effect was evident at rest and during stress (main effect of diet, p< 0.02). FMD increased (+34%) on the diet containing additional ALA. AVP also increased by 20%, and endothelin-1 was unchanged. These results suggest novel mechanisms for the cardioprotective effects of walnuts and flax, and further work is needed to identify the bioactives responsible for these effects. (Author’s abstract)