Cis-9, trans-11 conjugated linoleic acid is synthesized from vaccenic acid in lactating women

We studied the incorporation of the trans-11 vaccenic-1-C-13 acid (C-13-VA) into milk and endogenous synthesis of cis-9, trans-11 conjugated linoleic acid (CLA) in lactating women. Subjects (n = 4) were 247 +/- 30 d postpartum, weighed 70.8 +/- 3.7 kg, breast-fed at least 6 times/d and consumed self-selected diets. After an overnight fast, they consumed the 13C-VA (2.5 mg/kg body wt). Milk samples were obtained by complete breast expression at 0, 2, 4, 8, 12, 18, 24, and 48 h Post-C-13-VA ingestion. Lipid was extracted using chloroform: methanol. Fatty acids were methylated and converted to dimethyl disulfide and Diels-Alder derivatives before analysis by gas chromatography mass spectrometry. The mean 13 C-enrichment of milk VA was 3.1% at 8 h and reached maximal enrichment of 7.6% at 18 h. The 13 C enrichment of milk cis-9, trans-11 CLA reached a maximum of 0.4% at 18 h, confirming its conversion of VA to the Delta 9-desaturase enzyme product. In the subjects examined, a portion (< 10%) of the cis-9, trans-11 CLA present in milk was endogenously synthesized from VA.