Key Findings
For fatty acids (FA) to be utilised as biomarkers to predict dietary intake, dose–response curves that cover a spectrum of FA intake are required. Longer-term studies have found ALA, EPA and docosapentaenoic acid (DPA) increased in FA biomarkers with an increase in ALA intake with the data for DHA being less clear. In this study, the effect of short-term (14 days) supplementation with EPA and DHA (given as fish oil), across a range of doses, on plasma phosphatidylcholine (PC) n-3 FA levels and plasma lipid concentrations, along with the effect of short-term (14 days) ALA supplementation on plasma PC n-3 FA status in young, healthy women. An assessment of changes in plasma phosphatidylcholine (PC) n-3 FAs was conducted. The results demonstrate the FA composition of plasma PC to be a sensitive biomarker of n-3 LCPUFA intake, with small increases in EPA and DHA intake (from fish oil) being reflected within 14 days, in a dose-dependent fashion. EPA and DPA, two FA formed by the metabolic interconversion of ALA, were also increased with flaxseed oil supplementation, whilst DHA content remained unchanged. The synthesis of ALA to EPA, DPA and DHA occurs primarily in liver endoplasmic reticulum where there is competition between n-6 and n-3 FA for the same elongase and desaturase enzymes. The conversion of ALA may be downregulated by increased availability of conversion products; consumption of a fish compared to a beef-based diet decreased conversion of DPA to DHA. The discrepancy in findings between studies may be partly due to the higher doses of EPA plus DHA in the present study. The results show the dose-response relationship between EPA and DHA intake and plasma PC EPA and DHA mol% and μmol/L after 14 days of supplementation, in young healthy women. It was found that per g intake per day increases in EPA results in a 1.5 mol% or 76 μmol/L increases in plasma PC EPA abundance whilst per g intake per day increase in DHA results in an increase of 1.1 mol% or 61 μmol/L in plasma PC DHA abundance. These data highlight that even modest changes in dietary fat intake are reflected rapidly by plasma PC n-3 FA. In long term studies where n-3 FA biomarkers are only measured at the study beginning and end to determine compliance, it may be difficult to distinguish true compliers from noncompliers if measuring plasma lipid pools. The data highlight that short-term supplementation with ALA is reflected rapidly by plasma PC.
ABSTRACT
Although assumed, it remains unclear that fatty acid (FA) biomarkers of n-3 long-chain PUFA reflect wide ranges of intake. However, to be utilised as biomarkers, to predict dietary intake, dose-response curves that cover a spectrum of intakes are required. The aim of the study was to investigate whether the FA composition of plasma phosphatidylcholine (PC) is a sensitive biomarker of n-3 FAs from fish oil, across a range of supplementation doses, and alpha-linolenic acid (ALA) supplementation, in young, healthy women. A total of 303 young women were randomised to intakes ranging between 0.33 and 4.50 g EPA+DHA/day from fish oil (not all doses used in each year) or flaxseed oil (5.90-6.60 g/d) daily for 14 days in a series of trials, over 5 years. Fasting blood was collected at baseline (day 0) and day 14 and plasma PC FA composition, total and HDL-cholesterol and triglyceride concentrations measured. Fourteen days supplementation with fish oil significantly (P < 0.01) increased, in a dose-dependent fashion, plasma PC EPA, DPA and DHA at all doses except 1 and 3 mL/day. For the combined group of women who consumed any fish oil there was a 16% (P < 0.01) decrease in plasma triacylglycerol concentrations after 14 days supplementation. Flaxseed oil supplementation for 14 day resulted in significant (P < 0.01) increases in ALA, EPA and DPA, whilst DHA remained unchanged. Our data demonstrate plasma PC is a sensitive biomarker of n-3 FA intake and reflects changes within 14 days across a range of intakes.
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