Validation of the omega-3 fatty acid intake measured by a web-based food frequency questionnaire against omega-3 fatty acids in red blood cells in men with prostate cancer

BACKGROUND/OBJECTIVES: The objective of this study was to evaluate the ability of a web-based self-administered food frequency questionnaire (web-FFQ) to assess the omega-3 (omega-3) fatty acids (FAs) intake of men affected with prostate cancer (PCa) against a biomarker. SUBJECTS/METHODS: The study presented herein is a sub-study from a phase II clinical trial. Enrolled patients afflicted with PCa were included in the sub-study analysis if the FA profiles from the red blood cell (RBC) membranes and FA intakes at baseline were both determined at the time of the data analysis (n = 60). Spearman's correlation coefficients were calculated to estimate the correlations between FA intakes and their proportions in the RBC membranes. RESULTS: Intakes of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were highly correlated with their respective proportions in the RBC membranes (both r(s) = 0.593, P<0.0001). Correlation between alpha-linolenic acid (ALA) intake and its proportion in RBC was not significant (r(s) = 0.130, P = 0.332). Correlations were observed between fatty fish intake and total omega-3 FAs (r(s) = 0.304, P = 0.02), total long-chai omega-3 FAs (r(s) = 0.290, P = 0.03) and DHA (r(s) = 0.328, P = 0.01) in RBC membranes. CONCLUSIONS: This study has shown that the web-FFQ is an accurate tool to assess total long-chain omega-3 FAs, EPA and DHA but not ALA intake in clinical trials and epidemiological studies carried out in men with PCa.