Applied nutritional investigationDifferential plasma postprandial lipidomic responses to krill oil and fish oil supplementations in women: A randomized crossover study
Introduction
Marine oils containing long chain ω-3 fatty acids are common supplements available over the counter. The estimated total worldwide sales of these supplements in 2016 amounted to $33 billion [1]. There are several major sources of long chain ω-3 fatty acids, including fish oil (FO), krill oil (KO), and algal oils. KO differs from FO in the major lipid classes [2]. Indeed, in FO, triacylglycerols are the predominant lipid class (>98%), whereas in KO the lipid classes include phospholipids (mostly phosphatidylcholine [PC]), triacylglycerols, and free fatty acids (FFA). Furthermore, ω-3 fatty acids are found in all three of these lipid classes in KO [3].
There have been many studies on the incorporation of ω-3 fatty acids into blood and tissue lipids from marine oils, with a number of them, but not all, concluding that there is greater incorporation of ω-3 fatty acids into blood lipids from KO compared with FO [4], [5], [6], [7], [8], [9], [10], [11]. In fact, advertising for KO often mentions a greater bioavailability than FO, without a specific indication of whether this refers to ω-3 fatty acids or other components in the oils, such as carotenoids [12].
Four postprandial studies have investigated the incorporation of long chain ω-3 fatty acids into plasma from KO compared with FO [6], [7], [8], [9]. Two of these studies compared KO with reesterified triacylglycerols (TG) from FO or ethyl-ester concentrates of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from FO [6], [7]. The other two studies compared KO with FO [9] and krill meal [8]. The findings from these studies have not been consistent. The postprandial studies by Schuchardt et al. [7] and Yurko-Mauro et al. [6] reported that the incorporation of EPA and DHA into plasma phospholipids from KO was not significantly greater than FO. These studies also suggested that substantial variability between participants may have limited their capacity to detect significant differences between the study oils. Kohler et al. [8] reported a significantly greater incorporation of ω-3 fatty acids into the plasma phospholipids from KO than that of FO. Sung et al. [9] found that a lower dose of EPA from KO (70% of that provided from FO) resulted in a similar incorporation of EPA into plasma total lipid fatty acids. Moreover, out of three longer-term studies that compared KO with FO [6], [10], [11], only one [11] reported a significantly higher incorporation of EPA into plasma lipids from KO than that of FO.
All the studies referred to here used gas chromatography of the fatty acid methyl esters derived from the plasma lipid classes (TG, PL, total fatty acids) to compare KO with FO. Because KO and FO contain distinctly different lipid classes, a more effective approach to compare the incorporation of the two oils is to examine a wider plasma lipidome, enabling the detection and identification of hundreds of different lipid species, including the classes of interest [13], [14].
There have been no clinical studies comparing the postprandial incorporation of ω-3 fatty acids from KO and FO into different lipid molecular species; in other words, comparing the resulting postprandial plasma lipidomes. In recent years lipid analysis techniques have become increasingly available through the use of ultra-high-performance liquid chromatography, electrospray ionization–tandem mass spectrometry (UHPLC ESI-MS/MS) [15], [16]. This methodology gives greater detail about temporal patterns of fatty acid uptake into molecular species of lipids and allows more detailed understanding of the relative significance of the biochemical pathways being followed by the fatty acids [17], [18], [19]. The aim of this study was to examine the postprandial incorporation of long chain ω-3 fatty acids into different molecular species of plasma lipids after the ingestion of KO compared with FO. We hypothesized that the plasma lipidome would be differently affected by intakes of KO compared with FO.
Section snippets
Study participants
Ten healthy premenopausal women aged 18 to 45 y within a body mass index range of 20 to 30 (kg/m2) were recruited via e-mails to all Victoria University staff and students, and flyer advertisements in the Nutritional Therapy Teaching Clinic of the university, community centers, and local medical practices. Participants were screened for their suitability using a medical questionnaire and anthropometric measurements before enrolling into the study. The study was undertaken at Victoria University
Participant characteristics and intake of dietary long chain ω-3 PUFA at baseline
Ten healthy women completed the crossover study with KO and FO supplementations. Baseline measurements (mean ± standard deviation) included participant's age (28.5 ± 9.3 y), systolic blood pressure (113.0 ± 10.9 mm Hg), diastolic blood pressure (70.8 ± 9.9 mmHg), and a body mass index of 25.8 ± 3.6 (kg/m2). All participants completed a 24-h dietary recall on each study day, which was analyzed using FoodWorks Version 8. The daily intake of long chain ω-3 PUFA was 106 ± 91.0 mg. There was no
Discussion
The principal aim of this randomized crossover study was to compare the postprandial lipidomic responses to supplementation with KO and FO in healthy women over a 5-h postprandial period to understand the dynamic metabolism of the plasma lipids at the molecular species level. It is recognized that the amounts of long chain ω-3 fatty acids in the two study oils were not identical for practical reasons as stated in the Methods section (mainly blinding of participants). It is acknowledged that the
Conclusions
There were clear differences between KO and FO supplementations in the postprandial period, which were most noticeable in the changes in diacyl-phospholipids and ether-phospholipids. It is not known whether the changes identified in the short term translate to changes in the longer term. Further studies are required to validate the findings from this postprandial study through larger longer-term studies and to determine the potential health benefits associated with KO supplementation.
Acknowledgments
The authors are thankful to the study participants for their time and efforts to participate in the study. They would like to thank Mina Brock at CSIRO Tasmania for her assistance with the Iatroscan thin-layer chromatography–flame ionization analysis of the study oils. They also thank Dr Agus Salim (La Trobe University) for his invaluable help in setting up the linear mixed models.
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This work was supported by the College of Health and Biomedicine, Victoria University, Melbourne, Australia and the Operational Infrastructure Support scheme of the Victorian State Government, Victoria, Australia.
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P.J.M. and X.Q.S. are co-senior authors.