Plasma fatty acids: Biomarkers of dietary intake?

OBJECTIVE: To our knowledge, there is currently no consensus in the literature on the association between dietary fatty acids and circulating levels in plasma. The aim of this study was to assess the association of the intake of fatty acids with their relative plasma concentrations. METHODS: We conducted a study with 300 adults from the population-based health survey in São Paulo city (ISA-Capital 2008). We assessed demographic, lifestyle and anthropometric data, biochemical measurements, and two 24-h dietary recalls collected on non-consecutive days. Intake distribution was adjusted for intrapersonal variance to give usual dietary intake using the multiple source method (MSM). Percentage of fatty acids in plasma were analyzed by gas chromatography. The κ statistic, Spearman's correlation, and multiple linear regression (adjusted for confounders) and ratio limits of agreement were employed to determine the relationship between plasma and dietary measurements. RESULTS: Low correlation and agreement were found between dietary and plasma fatty acids. Docosahexaenoic acid (ß = 0.25; P < 0.001) and saturated (ß = 0.19; P = 0.048) fatty acids exhibited an association for means of intake adjusted by the MSM and for confounding variables. A large mean difference, with a large variation of "ratio limits," were observed between the measurements. CONCLUSION: Plasma and dietary polyunsaturated and saturated fatty acids exhibited low correlation and agreement, as well as weak association between each other. No association between intake and plasma concentrations of monounsaturated fat was found. Plasma fatty acids are not good biomarkers of food intake.