Effects of Diets High in Walnuts and Flax Oil on Hemodynamic Responses to Stress and Vascular Endothelial Function

January 1, 2010 Human Health and Nutrition Data 0 Comments

Effects of Diets High in Walnuts and Flax Oil on Hemodynamic Responses to Stress and Vascular Endothelial Function

Year: 2010
Authors: West, S.G. Likos Krick, A. Cousino Klein, L. Zhao, G. Wojtowicz, T.F. McGuiness, M. Bagshaw, D.M. et. al.
Publication Name: Journal of the American College of Nutrition
Publication Details: Volume 29; Number 6; Pages 595 – 603.


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)
These researchers have previously reported that diets high in PUFA from walnuts and flax significantly reduce C-reactive protein (CRP) and several markers of inflammation and endothelial dysfunction in adults with high cholesterol. Flax oil and walnuts are a concentrated source of alpha-linolenic acid (ALA), an omega-3 fatty acid that may be responsible for improvements in lipids and endothelial function. In some epidemiologic studies, higher consumption of ALA is associated with lower diastolic blood pressure and lower risk of ischemic heart disease. Several small studies have reported significant reductions in neuroendocrine and cardiovascular responses to psychological stress after treatment with omega-3 fatty acids from marine or plant sources. Attenuated cardiovascular reactivity to stress may be an additional mechanism through which ALA reduces coronary risk. In this study, the diet-related change in blood pressure and total peripheral resistance responses to standardized laboratory stressors, serum fatty acid concentrations, and vasoactive hormones in 20 adults with elevated LDL-C  enrolled in a randomized, controlled feeding study in which the ALA levels were manipulated were examined. The FMD of the brachial artery was assessed at the end of each diet period in a subset of patients.  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 LDLC, the 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 FMD. Furthermore, the magnitude of changes was correlated, and this suggests that improvements in vascular endothelial function may result from the anti-inflammatory effects of ALA or other constituents of flax oil. The findings suggest that the effects of ALA on endothelial function and CRP are dose
dependent, although dose and the source of ALA. After both of the experimental diets, reductions in diastolic blood pressure were proportional to the increase in serum concentrations of DPA (C22:5 n3). 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. It appears that the anti-inflammatory effects of ALA are not entirely dependent on conversion to long chain omega-3 fatty acids. There is also evidence that ALA improves endothelial function acutely. Reductions in blood pressure following a diet high in ALA resulted from significant reductions in systemic vascular resistance. Subjects with larger increases in serum concentrations of PUFA exhibited larger decreases in diastolic blood pressure. This article identifies novel mechanisms for the cardiovascular benefits of PUFA contained in walnuts and flax. Taken together with reductions in LDL-C and inflammation, these improvements in endothelial function and cardiovascular responses to stress would be expected to significantly reduce the risk of CVD. (Editor�s comments)

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