Article

Acute Effects of High-Fat Meals Enriched With Walnuts or Olive Oil on Postprandial Endothelial Function

Departament de Medicina, Universitat Autònoma de Barcelona, Barcelona, Spain.
Journal of the American College of Cardiology (Impact Factor: 15.34). 11/2006; 48(8):1666-71. DOI: 10.1016/j.jacc.2006.06.057
Source: PubMed

ABSTRACT We sought to investigate whether the addition of walnuts or olive oil to a fatty meal have differential effects on postprandial vasoactivity, lipoproteins, markers of oxidation and endothelial activation, and plasma asymmetric dimethylarginine (ADMA).
Compared with a Mediterranean diet, a walnut diet has been shown to improve endothelial function in hypercholesterolemic patients. We hypothesized that walnuts would reverse postprandial endothelial dysfunction associated with consumption of a fatty meal.
We randomized in a crossover design 12 healthy subjects and 12 patients with hypercholesterolemia to 2 high-fat meal sequences to which 25 g olive oil or 40 g walnuts had been added. Both test meals contained 80 g fat and 35% saturated fatty acids, and consumption of each meal was separated by 1 week. Venipunctures and ultrasound measurements of brachial artery endothelial function were performed after fasting and 4 h after test meals.
In both study groups, flow-mediated dilation (FMD) was worse after the olive oil meal than after the walnut meal (p = 0.006, time-period interaction). Fasting, but not postprandial, triglyceride concentrations correlated inversely with FMD (r = -0.324; p = 0.024). Flow-independent dilation and plasma ADMA concentrations were unchanged, and the concentration of oxidized low-density lipoproteins decreased (p = 0.051) after either meal. The plasma concentrations of soluble inflammatory cytokines and adhesion molecules decreased (p < 0.01) independently of meal type, except for E-selectin, which decreased more (p = 0.033) after the walnut meal.
Adding walnuts to a high-fat meal acutely improves FMD independently of changes in oxidation, inflammation, or ADMA. Both walnuts and olive oil preserve the protective phenotype of endothelial cells.

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    • "A sample size of 40 subjects per each of the three centers (120 in total) was determined based on endothelial function as the primary outcome. Endothelial function was intended to be assessed by flow mediated dilatation (FMD) The anticipated difference in means was 20% and the standard deviation was 1.35 [34]. Aforementioned sample size was sufficient to detect this difference with a power of 0.8 at a significance of 0.05. "
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    • "On the other hand, studies that tested the postprandial effect of nuts consumed in the context of a meal usually showed antioxidant effects [23,27]. In addition, walnut meals were shown to acutely improve endothelial function [48] and reduce the postprandial inflammatory response in mononuclear cells in humans [24]. "
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    • "A number of studies have investigated the effect of isoenergetic meals of different fatty acid composition on measures of vascular function and substantial differences in study design has led to difficulties in drawing conclusions [8]. In addition, some studies tested healthy subjects [38,44-48] whilst other investigated hyercholesterolaemic patients [49], type two diabetics [50,51] or adults with the metabolic syndrome [52]. The overall evidence suggests a moderate decrease in vascular function following a SFA-rich meal [8] but the data are less consistent when SFA is replaced by MUFA. "
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