trans Fatty acids in human milk are inversely associated with concentrations of essential all-cis n-6 and n-3 fatty acids and determine trans, but not n-6 and n-3, fatty acids in plasma lipids of breast-fed infant

Background: Human milk fatty acids vary with maternal dietary fat compositi on. Hydrogenated dietary oils with trans fatty acids may displace cis n-6 a nd n-3 unsaturated fatty acids or have adverse effects on their metabolism. The effects of milk trans, n-6, and n-3 fatty acids in breast-fed infants are unclear, although n-6 and n-3 fatty acids are important in infant growt h and development. Objective: We sought to determine the relations between trans and cis unsat urated fatty acids in milk and plasma phospholipids and triacylglycerols of breast-fed infants, and to identify the major maternal dietary sources of trans fatty acids. Design: We collected milk from 103 mothers with exclusively breast-fed 2-mo -old infants, blood from 62 infants, and 3-d dietary records from 21 mother s. Results: Mean (+/-SEM) percentages of trans fatty acids were as follows: mi lk, 7.1 +/- 0.32%; infants' triacylglycerols, 6.5 +/- 0.33%; and infants' p hospholipids, 3.7 +/- 0.16%. Milk trans fatty acids, alpha-linolenic acid ( 18:3n-3), arachidonic acid (20:4n-6), docosahexaenoic acid (22:6n-3) (P < 0 .001), and linoleic acid (18:2n-6) (P = 0.007) were each related to the sam e fatty acid in infant plasma phospholipids. Milk trans fatty acids were in versely related to milk 18:2n-6 and 18:3n-3, but not to milk or infant plas ma 20:4n-6 or 22:6n-3. trans Fatty acids represented 7.7% of maternal total fat intake (2.5% of total energy); the major dietary sources were bakery p roducts and breads (32%), snacks (14%), fast foods (11%), and margarines an d shortenings (11%). Conclusions: There were comparable concentrations of trans fatty acids in t he maternal diet, breast milk, and plasma triacylglycerols of breast-fed in fants. Prepared foods were the major dietary source of trans fatty acids.