Trans-vaccenic acid (TVA) is a natural trans fatty acid found in ruminant food produce. It is converted to the cis-9, trans-11 isomer of conjugated linoleic acid (c9, t11-CLA) by the action of stearoyl-CoA desaturase (SCD) in tissue. c9, t11-CLA has been associated with anti-inflammatory effects and also affects lipid metabolism. The aim of the present study was to determine if TVA is bioconverted to c9, t11-CLA in intestinal epithelial cells and to ascertain whether TVA has effects similar to c9, t11-CLA on markers of inflammation relevant to inflammatory bowel disease. The present study demonstrated that TVA treatment led to significant bioconversion into c9, t11-CLA in Caco-2 cells. Treatment with both TVA and c9, t11-CLA resulted in alteration of cellular fatty acid profile and SCD activity in the Caco-2 cell line. However, CLA, but not TVA, significantly modulated transcription of TNF-α, IL-12, IL-6 and production of IL-12 by these cells. Thus the present study established that TVA treatment can alter SCD desaturation indices and induce compositional changes in the fatty acid profile of the Caco-2 cell model of the human intestinal epithelium but this is not associated with functional effects on markers of the inflammatory response.

The aim of the present study was to find out whether the incorporation of organic dairy and meat products in the maternal diet affects the contents of the conjugated linoleic acid isomers (CLA) and trans-vaccenic acid (TVA) in human breast milk. To this purpose, milk samples from 312 breastfeeding mothers participating in the KOALA Birth Cohort Study have been analysed. The participants had documented varying lifestyles in relation to the use of conventional or organic products. Breast milk samples were collected 1 month postpartum and analysed for fatty acid composition. The content of rumenic acid (the main CLA) increased in a statistically significant way while going from a conventional diet (no organic dairy/meat products, 0·25 weight % (wt%), n 186) to a moderately organic diet (50–90 % organic dairy/meat, 0·29 wt%, n 33, P = 0·02) and to a strict organic diet (>90 % organic dairy/meat, 0·34 wt%, n 37, P ≤ 0·001). The levels of TVA were augmented among the participants with a moderately organic diet (0·54 wt%) and those with a strict organic diet (0·59 wt%, P ≤ 0·001), in comparison with the conventional group (0·48 wt%). After adjusting for covariables (recruitment group, maternal age, maternal education, use of supplements and season), statistical significance was retained in the group of the strict organic dairy users (P < 0·001 for rumenic acid). Hence, the levels of CLA and TVA in human milk can be modulated if breastfeeding mothers replace conventional dairy and/or meat products by organic ones. A potential contribution of CLA and TVA to health improvement is briefly discussed.

The aim of this human intervention study was to evaluate the Δ9-desaturation of trans-11–18:1 (trans-vaccenic acid; tVA) to cis-9,trans-11–18:2 (c9,t11 conjugated linoleic acid; CLA) and of trans-12–18:1 (t12) to cis-9,trans-12–18:2 after a short-term (7d) and a long-term (42d) supplementation period. The conversion rates of both trans-18:1 isomers were estimated by lipid analysis of serum and red blood cell membranes (RBCM). Subjects started with a 2-week adaptation period without supplements. During the 42d intervention period, the diet of the test group was supplemented with 3g/d of tVA and 3g/d of t12. The diet of the control group was supplemented with a control oil. Serum tVA and t12 levels in the test group increased by fivefold and ninefold after 7d, respectively, and by eight- and 12-fold after 42d, respectively, when compared with the adaptation period (p≤0·002). The serum c9,t11CLA levels increased by 1·7- and 2·0-fold after 7d and 42d, respectively (p≤0·001). After 42d, the test group's RBCM c9,t11CLA content was elevated by 20% (p=0·021), whereas in the control group it was decreased by 50% (p=0·002). The conversion rate of tVA was estimated at 24% by serum and 19% by RBCM. No increase in c9,t12–18:2 was observed in the serum and RBCM, and thus no conversion of t12 could be determined. In conclusion, the endogenous conversion of dietary tVA to c9,t11CLA contributes approximately one quarter to the human CLA pool and should be considered when determining the CLA supply.