The aim of this human intervention study was to evaluate the D9-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 (7 d) and a long-term (42 d) 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 42 d intervention period, the diet of the test group was supplemented with 3 g/d of tVA and 3 g/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 7 d, respectively, and by eight-and 12-fold after 42 d, respectively, when compared with the adaptation period (P#0·002). The serum c9,t11 CLA levels increased by 1·7-and 2·0-fold after 7 d and 42 d, respectively (P#0·001). After 42 d, the test group's RBCM c9,t11 CLA content was elevated by 20 % (P¼ 0·021), whereas in the control group it was decreased by 50 % (P¼ 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,t11 CLA contributes approximately one quarter to the human CLA pool and should be considered when determining the CLA supply.

Dietary supplementation with conjugated linoleic acid (CLA) has been shown to reduce body fat mass. To investigate the effects of individual CLA isomers on the fatty acid profiles of lipogenic (liver and white adipose) and lipid sensitive (erythrocyte) tissues, BALB/c mice were fed with 1 of 2 diets supplemented with either a c9,t11-CLA-enriched and t10,c12-CLA-free or a CLA-mixture containing both isomers in equal amounts (1% w/w of the diet) for 5 weeks. A control group was fed with a diet enriched in sunflower oil to energy balance the CLA. Compared to the t10,c12-CLA-free and the control diets, we observed a significant reduction of adipose tissue accompanied by fatty livers in the CLA-mix-fed group. These alterations in body fat distribution entailed a conspicuous shift of the fatty acid profiles of adipose tissue and livers. Liver enlargement was mainly caused by accumulation of C18 monoenes that accounted for 67 ± 1% of total fatty acid methyl esters. The significant reduction of the 18:0/18:1 desaturation index in the liver upon CLA-mix diet indicated high stearoyl-CoA desaturase activity. In contrast, reduction in white adipose tissue was largely driven by percental reduction of monounsaturated fatty acids (p ≤ 0.001). 16:0/ 16:1 and 18:0/18:1 desaturation indices for white adipose tissue significantly increased, suggesting an inhibition of stearoyl-CoA desaturase upon CLA-mix diet. The fatty acid profile of the erythrocytes widely reflected that of livers, depending on the supplemented diet. These profound changes in fatty acid composition of lipogenic organs due to t10,c12-CLA intake may be the consequence of function- al alterations of lipid metabolism.

In 3 experiments with a total of 113 growing pigs, supplements of 1,000 to 9,000 IU vitamin A or 2 to 100 mg beta-carotene to vitamin A and beta-carotene free grains soyabean-meal-diets were tested. The liver samples were taken by biopsy or after slaughtering. The error of biopsy sampling was defined in preliminary experiments. The initial liver vitamin A depots were checked by slaughtering of 5 piglets of each group. The vitamin A content was analyzed by the anhydromethod or fluorometrically. In all 3 experiments, the different vitamin or provitamin intake did not influence feed intake and growth at any time. Highly significant linear relations were found between the intake of vitamin A or beta-carotene and the storage in the liver. Due to the higher relative liver weight, younger animals had a lower vitamin A concentration in this organ. Related to the tested beta-carotene dose of 2, 4, 8, 50 and 100 mg/kg feed, a vitamin A activity of 360, 320, 290, 130 and 80 micrograms retinol equivalents per mg beta-carotene was found. The conversion of beta-carotene into vitamin A decreases inversely to the beta-carotene intake. The vitamin A activity of synthetic beta-carotene which is higher than the beta-carotene analyzed in feedstuffs is discussed.