trans Fatty acids in milk produced by women in the United States

Background: trans Fatty acids (FAs) have been identified as negatively affecting human health. The trans FA composition of human milk fat must be examined to establish its influence on the nutritional quality of milk consumed by infants. Objective: We sought to ascertain the individual and total trans FA isomers (sum of FAs containing at least one trans double bond) in human milk and to identify relations between individual FAs and milk fat concentration (% by wt). Design: The FA composition of milk samples (n = 81) from women living in the southwestern United States was ascertained. The individual 18:1t isomers were separated. Correlations between each FA, total trans FAs, groups of similar FAs, and milk fat concentrations were examined. Results: The mean total trans FA concentration was 7.0 ± 2.3% (range: 2.5-13.8%). The concentration of total 18:1t was 5.1 ± 2.0% (range: 1.5-11.6%), and Δ10t (range: Δ9-12t) was the most abundant isomer. Conclusions: Milk fat from women living in the United States contains concentrations of trans FAs similar to those in milk from Canadian women but greater than those reported in milk from women in other countries. In decreasing order of concentration, the Δ10t, Δ11t, Δ9t, and Δ12t isomers represented 78.9% of the total 18:1t. These FAs generally originate from partially hydrogenated vegetable oils and ruminant fat in the diet. No relation was found between the concentration of total trans FAs and milk fat concentration.