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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Cis-9, Trans-11 Conjugated Linoleic Acid Is Synthesized from Vaccenic Acid in Lactating Women¹

² Department of Animal and Veterinary Science, College of Agricultural and Life Sciences, University of Idaho, Moscow, ID 83844–2330 and ³ Department of Food Science and Human Nutrition, Washington State University, Pullman, WA 99164–6376

^* To whom correspondence should be addressed. E-mail: mmcguire{at}uidaho.edu.

We studied the incorporation of the trans-11 vaccenic-1-¹³C acid (¹³C-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-¹³C-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 ¹³C-enrichment of milk VA was 3.1% at 8 h and reached maximal enrichment of 7.6% at 18 h. The ¹³C enrichment of milk cis-9, trans-11 CLA reached a maximum of 0.4% at 18 h, confirming its conversion of VA to the 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.