Trans fatty acid isomers in Canadian human milk.

The fatty acid composition, total trans content (i.e., sum of all the fatty acids which may have one or more trans double bonds) and geometric and positional isomer distribution of unsaturated fatty acids of 198 human milk samples collected in 1992 from nine provinces of Canada were determined using a combination of capillary gas-liquid chromatography and silver nitrate thin-layer chromatography. The mean total trans fatty acid content was 7.19 +/- 3.03% of the total milk fatty acids and ranged from 0.10 to 17.15%. Twenty-five of the 198 samples contained more than 10% total trans fatty acids, and thirteen samples contained less than 4%. Total trans isomers of linoleic acid were 0.89% of the total milk fatty acids with 18:2 delta 9c,13t being the most prevalent isomer, followed by 18:2 delta 9c,12t and 18:2 delta 9t,12c. Using the total trans values in human milk determined in the present study, the intake of total trans fatty acids from various dietary sources by Canadian lactating women was estimated to be 10.6 +/- 3.7 g/person/d, and in some individuals, the intake could be as high as 20.3 g/d. The 18:1 trans isomer distribution differed from that of cow's milk fat but was remarkably similar to that in partially hydrogenated soybean and canola oils, suggesting that partially hydrogenated vegetable oils are the major source of these trans fatty acids.