Circulating fatty acids as biomarkers of dairy fat intake: Data from the Lifelines Biobank and Cohort Study.

Background: C14:0, C15:0, C17:0 and trans-C16:1(n-7) are often used as biomarkers for dairy fat intake. Trans-C18:1(n-7) and CLA, two fatty acids which are also present in dairy, have hardly been explored. We investigated whether trans-C18:1(n-7) and CLA can enrich the existing biomarker portfolio.Methods: Data were obtained from Lifelines (n=769). Dairy fat intake was determined by FFQ. Fatty acids were measured in fasting plasma triglycerides (TG), phospholipids (PL) and cholesterol esters (CE).Results: Median (25th-75th percentile) intakes of dairy and dairy fat were 322(209-447) and 12.3(8.4-17.4) g/d respectively. A pilot study showed that trans-C18:1(n-7) and CLA were only detectable in TG and PL. Of the established markers, TG C15:0 was most strongly associated with dairy fat intake (standardized (std.)=0.286, R-2=0.111). Of the less established markers, TG trans-C18:1(n-7) was most strongly associated with dairy fat intake (Std.=0.292, R-2=0.115), followed by PL CLA (Std.=0.272, R-2=0.103) and PL trans-C18:1(n-7) (Std.=0.269, R-2=0.099). In TG, a combination of C15:0 and trans-C18:1(n-7) performed best (R-2=0.128). In PL, a combination of C14:0, C15:0, trans-C18:1(n-7) and CLA performed best (R-2=0.143).Conclusion: Trans-C18:1(n-7) and CLA can be used as biomarkers of dairy fat intake. Additionally, combining established with less established markers allowed even stronger predictions for dairy fat intake.