Twice weekly intake of farmed Atlantic salmon (Salmo salar) positively influences lipoprotein concentration and particle size in overweight men and women

Abstract

The US Dietary Guidelines for Americans recommend twice weekly fish intake. Farmed Atlantic salmon is a good source of omega-3 (n-3) fatty acids which have positive lipid modifying effects; however, it is unknown whether these responses are dose-dependent. Our primary research objective was to determine the effect of dose-dependent intake of farmed Atlantic salmon on lipoprotein particle (P) size and concentration. We hypothesized that low-density lipoprotein (LDL)–P and high-density lipoprotein (HDL)–P size and concentration would increase with salmon intake in a dose-dependent manner. Overweight, adult participants (n = 19) were enrolled in a cross-over designed clinical trial evaluating intake of farmed Atlantic salmon. In random order, participants were assigned to 90, 180, or 270 g of salmon twice weekly for 4-week dietary treatments. Following a 4- to 8-week washout, participants crossed over to another dose of fish intake until all treatments were completed. Plasma lipid concentrations were determined and serum lipoprotein concentrations and particle size were determined by nuclear magnetic resonance. Intake of salmon reduced plasma and serum triglyceride (TG) concentrations and increased plasma HDL-C concentrations. The concentrations of large very low-density lipoprotein (VLDL)–P and chylomicron (CM)–P were reduced. Large LDL-P concentrations were increased in a dose-dependent manner. The mean size of VLDL-P was reduced and that of LDL was increased. Total TG was reduced as was the TG content of VLDL-P and CM-P. Twice weekly intake of farmed Atlantic salmon portions influences lipoprotein particle size and concentration in a manner associated with cardiovascular disease risk reduction.

Introduction

Clinically, lipoprotein concentrations are evaluated to determine the risk of atherosclerosis [1]. Elevated concentrations of high-density lipoprotein cholesterol (HDL-C) and low concentrations of low-density lipoprotein cholesterol (LDL-C) are associated with reduced risk. Elevations in fasting and/or postprandial TG concentrations are seen to be atherogenic [2]. The lipoproteins responsible for transport of lipids include chylomicron (CM), very low-density lipoprotein (VLDL), LDL, and HDL with the classifications based upon the relative content of lipid and protein in each. The composition and physical structure of lipoprotein molecules is in constant flux and changes as the core contents are taken up by peripheral tissues The cholesterol and TG composition within the lipoprotein classes vary among individuals as a result of genetics [3], [4], lifestyle [5], [6], including diet [7], [8], and drug therapy [9], [10].

Elevated total and LDL-C and TG are associated with cardiovascular disease (CVD) risk; however, disease occurs among people with normal lipid levels [1]. Variation in the concentration and size of lipoprotein particles (P), particularly LDL-P and HDL-P, has an impact on their function and relationship to atherosclerosis development [11], [12]. Individuals who have normal concentrations of cholesterol that are distributed in small, dense LDL-P may be at increased risk of coronary heart disease [13]. LDL-P size is an important CVD risk factor that correlates inversely with sub-clinical atherosclerosis as measured by intima-media thickening [14]. Although the total HDL-C concentration is associated with reduced CVD [15], it has been shown that, like LDL-P, small dense HDL-Ps are positively associated with increased risk of CVD [16] while an increased concentration of large HDL-Ps is considered protective [17], [18]. VLDL-Ps are positively associated with CVD risk but a lower concentration of large VLDL-P is associated with reduced risk [16].

Consuming fatty fish and fish oil is associated with reduction of fatal coronary events [19]. The protective effect of fatty fish intake is ascribed to their content of the long-chain (LC) omega-3 (n-3) fatty acids [20] eicosapentaenoic acid (EPA) (20:5n-3) and docosahexaenoic acid (DHA) (22:6n-3). Supplementation with LCn-3 is an accepted therapy for the reduction of elevated blood TG levels [21], [22] although it typically also results in increases in total cholesterol, HDL-C and LDL-C concentrations [23]. Controlled feeding studies show that fish intake increases large HDL-P concentrations [24], [25]. Fish oil supplementation increases the content of large HDL-P and large LDL-P and reduces the size and concentration of VLDL-P [26], [27], all changes that are associated with reduced risk of CVD [12].

The research objective of this study was to determine whether the intake of farmed Atlantic salmon (Salmo salar) would modify lipoprotein particle size and concentration in a manner associated with reduced CVD risk. Specifically, we hypothesized that LDL-P and HDL-P concentration and size would increase with salmon intake in dose-dependent manner. To test this hypothesis we performed an analysis of lipoprotein particle size and concentrations in a randomized, crossover-designed trial in which participants were fed 90 g, 180 g, and 270 g of farmed Atlantic salmon twice weekly in 4-week treatments.