a1 Lehrstuhl für Ernährungslehre, Department für Lebensmittel und Emährung, Technische Universität München–Weihenstephan, Alte Akademie 16, D-85350 Freising, Germany
a2 Deutsches Krebsforschungszentrum, Abteilung für Klinische Epidemiologie, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany
Objective: The habitual intake of the conjugated linoleic acid (CLA) isomer C18:2 c9t11 (rumenic acid, RA) was assessed and compared with plasma biomarkers.
Design: The newly developed food-frequency questionnaire (FFQ) comprised 46 food items and was validated by means of a 7-day estimated record (7-d ER). Additionally, the dietary intake results of the FFQ, 7-d ER, the last day (1-d ER) and the last two days (2-d ER) before blood sampling of the 7-d ER were compared to the content of C18:2 c9t11 in plasma phospholipids (PL) and triglycerides (TG) as possible biomarkers.
Setting: Metabolic unit of a university institute.
Subjects: Fifty-seven students completed both dietary instruments. From all participants fasting blood samples were taken.
Results: Mean daily intake of rumenic acid was 246 mg day−1 and 323 mg day−1 as measured by the FFQ and the 7-d-ER, respectively. The degree of correspondence between both assessment methods was acceptable; this is indicated by a total kappa value of κ = 0.31 (P < 0.01) and a Pearson correlation coefficient of r = 0.46 (P < 0.01). Rumenic acid content in plasma triglycerides was twice as high as found in phospholipids. The correlation between the intake results gained with the 7-d ER and the plasma PL contents of C18:2 c9t11 was statistically significant; this was also true for the C18:2 c9t11 values in plasma TG compared with the intake results of one or two days before blood sampling.
Conclusions: Regarding RA intake, the FFQ data revealed an acceptable degree of correspondence with the 7-d ER data but failed to show significant correlations to the potential biomarkers. However, with respect to the results of the 7-d ER, the RA content in plasma PL and TG are possible biomarkers of short-term and medium-term intake, respectively.
(Received January 29 2001)
(Accepted June 15 2001)