Palmolein and olive oil consumed within a high protein test meal have similar effects on postprandial endothelial function in overweight and obese men: A randomized controlled trial
Introduction
Reducing saturated fatty acid (SFA) intake has been a key dietary strategy for lowering coronary heart disease (CHD) risk based primarily on its cholesterol raising effects [1], [2]. However, recent evidence suggests this relationship may not be as straightforward [1], [3] and may be affected by co-consumption of other dietary components. Meals or foods high in SFA may contain other constituents that counteract its CHD potential [1]. Furthermore, dietary effects on CHD risk are mediated through multiple pathways; it is therefore insufficient to base dietary recommendations solely on its lipid modulating effects and evaluating the effects of SFA on multiple biomarkers will assist to characterize its CHD potential [1].
Endothelial dysfunction, involving increased endothelial permeability to lipoproteins and other plasma constituents, reduced vasodilatation and activation of thrombotic and inflammatory pathways has been proposed as the earliest identifiable event in the atherosclerosis process and therefore represents an important clinical target for cardiovascular disease (CVD) prevention through dietary interventions [4], [5]. To date, the effects of SFA on vascular function have not been well-researched [2], [6]. Considering most humans spend the majority of their day in the postprandial state, it is important to investigate the acute effects of fat-containing meals on endothelial function. High-fat meals have previously been shown to impair postprandial vascular function as indicated by reduced brachial artery flow-mediated dilatation (FMD) [6], a recognized marker of endothelial dysfunction [7], and increased markers of vascular function such as cell adhesion molecules including vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1) and E-selectin [8]. This effect may be ascribed to increased inflammation and oxidative stress mediated by elevated non-esterified fatty acids and postprandial triglyceride rich lipoproteins [6]. However, evidence for the differential postprandial effects of SFA vs. unsaturated fatty acids on vascular function is inconclusive [6] and may be dependent on other concurrent meal components such as protein. Westphal et al. [9] showed that consumption of SFA from dairy (whipped cream) had a neutral effect on FMD postprandially when consumed with a 50 g protein load (soy protein, caseinate). This response may be due to the presence of the amino acid l-arginine in the meals [10]. This suggests consumption of SFA in combination with a high protein and/or l-arginine load provided by dietary sources such as fish, meat (beef, poultry, pork), seeds, nuts and soy [11] may not impair FMD and endothelial function.
Palmolein, derived from dry fractionation of palm oil is a rich source of both SFA (42%) and unsaturated fat (47% monounsaturated fatty acids (MUFA), 12% polyunsaturated fatty acids (PUFA)) (Table 1). It's inherent stability and resistance to oxidation makes it a popular choice for food manufacturers and as replacement for trans fats [12], [13]. Hence, assessing its health effects is important.
The aim of this study was to assess postprandial effects of typical meals high in protein containing either palmolein or olive oil on endothelial function in overweight or obese men, a target group with high prevalence globally [14] with increased risk of endothelial dysfunction [15]. We hypothesized that palmolein relative to olive oil, in the context of a high protein meal, will have similar effects on endothelial function as assessed by FMD as primary outcome. Secondary outcomes were circulating markers of endothelial function including serum adhesion molecules (VCAM-1, ICAM-1 and E-Selectin), endothelium derived fibrinolytic factors (plasminogen activator inhibitor-1 [PAI-1], tissue plasminogen activator [tPA]), a marker of oxidative stress (nitrotyrosine formation), insulin, glucose and triglycerides.
Section snippets
Methods
The dietary intervention (http://www.anzctr.org.au; ACTRN12613000136707) was conducted at CSIRO's Nutrition and Health Research Clinic, Adelaide, South Australia between September and December 2013 according to the guidelines of the National Health and Medical Research Council National Statement on Ethical Conduct in Human Research. Ethical approval for the trial was obtained from the CSIRO Human Ethics Committee reference 12/13 and written informed consent was obtained from all participants.
Results
The participant flow through the study is summarized in Fig. 1. A total of 28 participants completed both treatments and were included in the statistical analysis. Participant baseline characteristics are summarized in Table 2. FMD levels were similar to those previously reported in overweight/obese populations [20], [21].
The postprandial effects of the test meals on FMD are illustrated in Fig. 2. The postprandial FMD response did not change, and there were no differences in FMD responses
Discussion
This study showed consumption of a high protein meal containing fats differing in saturated fat, palmolein or olive oil, had no effect on postprandial FMD and markers of vascular function (serum ICAM-1, E-selectin) and similar increases in triglycerides. Both meals decreased plasma tPA and PAI-1 which may have been related to a diurnal response [22], unrelated to meal consumption. Plasma nitrotyrosin, a marker of oxidative stress, transiently increased 1 h after consumption of the olive oil
Contribution of authors
WS: Main author of the manuscript; managed the conduct of the research; performed statistical analysis.
GB: Designed research (project conception, development of overall research plan, study oversight); oversight of statistical analysis; critical revision of the manuscript and approval of the final version.
MN: Designed research (project conception and development of overall research plan, and study oversight); critical revision of the manuscript and approval of the final version.
Funding source
Malaysian Palm Oil Board (Kuala Lumpur, Malaysia) provided funding and palmolein. The funder had no influence over the study design, conduct of the research, analysis and report of the data.
Disclosures
None of the authors had any conflict of interest in relation to this manuscript.
Conflicts of interest
WS, GB, MN do not have any conflict of interest.
Acknowledgments
The authors would like to thank all supporting staff and the participants of the study.
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