The occurrence of trans-18 : 1 isomers in plasma lipids classes in humans

Objective: The aim of this study was to examine the distribution of trans f atty acids (TFA) in plasma lipid classes and the relationship with dietary intake of TFA. Design: After a 2 week baseline (habitual) diet, all subjects consumed a mo derate fat (MF) diet for 3 weeks with the fat being derived mainly from mar garine and the rest from lean beef, and then a very low fat (VLF) diet for 3 weeks with the TFA being derived only from the lean beef. Blood samples w ere collected 2 days prior to the end and also on the last day of each diet ary period. Setting: Deakin Institute of Human Nutrition, Deakin University, Geelong, A ustralia. Subjects: Ten free-living mildly hypercholesterolaemic subjects aged 22-66 were recruited in Geelong. Outcome measures: TFA intake was calculated from analyses of Australian mar garines, butter, lean meat and animal fat. The TFA in plasma lipid fraction s were separated by AgNO3 thin-layer chromatography and quantitated by capi llary gas-liquid chromatography using internal standards. Results: The phospholipid (PL) fraction contained more than 60% of the tran s-18:1 isomers in the plasma lipids in all subjects. On the baseline diet, the predominant positional isomer of trans-18:1 in PL was Delta 11, whereas in the other lipid classes it was the Delta9 isomer. The concentration of the Delta9 isomer increased on the MF diet, particularly in the PL fraction , while the concentration of the Delta 11 isomer decreased in all fractions . On the VLF diet, the total TFA level decreased by approximately 50%, main ly due to decreases in the TFA isomers in the PL and TG fractions. Changes in plasma total and PL TFA, PL Delta9. Delta 10 and Delta 11 were strongly correlated with dietary TFA intake (P < 0.0001). There were also significan t association between dietary TFA intake and PL <Delta>12 (P = 0.003), tria cylglycerol Delta9 (P = 0.009), Delta 11 (P = 0.0005), total triacylglycero l (P = 0.023) and free fatty acid TFA (P = 0.042). Conclusions: The results suggest that the measurement of trans-18:1 in plas ma PL and TAG, and plasma total TFA could be used to estimate the intake of TFA. Sponsorship: Meat Research Corporation of Australia.