Dietary trans fatty acids affect the essential fatty-acid concentration of rat milk

Increasing efforts have been made to determine the distribution and concentration of trans fatty acids in milk, due to the importance of lipids in infant growth and development. In general, trans fatty acid concentration of milk reflects trans fatty acid intake, but insufficient data are available to assess the effects of dietary trans fatty acids on maternal milk. Thus, controlled studies are needed to establish whether there is a dose-response relationship and whether trans fatty acids could affect the concentration of essential fatty acids (EFA), long-chain polyunsaturated fatty acids (PUFA) and the (n-6)/(n-3) ratio in milk. Three groups of six rats each were fed for 10 wk one of three diets differing in trans fatty acid concentration (Control, 0 mol/100 mol; high trans concentration (H), 14.5 mol/100 mol; very high trans concentration (VH), 30 mol/100 mol), but containing the same proportions of linoleic and alpha-linolenic acids and a ratio of 18:2(n-6)/18:3(n-3) of about 7:1. Trans fatty acids were incorporated into maternal milk in a dose-dependent manner. In addition, rats fed trans isomers had greater linoleic acid levels than controls. The proportion of alpha-linolenic acid in milk was lower in the VH group, and the (n-6)/(n-3) cis PUFA ratio in milk of the VH group was greater than that in controls. Total long-chain PUFA levels did not differ among groups. These results suggest that high intakes of trans fatty acids affect the EFA concentration but not that of long-chain PUFA of rat milk, provided that EFA are supplied in sufficient amounts.