Effect of dietary conjugated linoleic acid (CLA) on metabolism of isotope-labeled oleic, linoleic, and CLA isomers in women

The purpose of this study was to investigate the effect of dietary CLA on accretion of 9c-18:1, 9c, 12 c-l 8:2, 10t,12 c-l 8:2, and 9c,11t-18:2 and conversion of these FA to their desaturated, elongated, and chain-shortened metabolites. The subjects were six healthy adult women who had consumed normal diets supplemented with 6 g/d of sunflower oil or 3.9 g/d of CLA for 63 d. A mixture of 10t,12c-18:2-d(4), 9c,11t-18:2-d(6), 9c-18:1-d(8), and 9c,12c-18:2-d(2), as their ethyl esters, was fed to each subject, and nine blood samples were drawn over a 48-h period. The results show that dietary CLA supplementation had no effect on the metabolism of the deuterium-labeled FA. These metabolic results were consistent with the general lack of a CLA diet effect on a variety of physiological responses previously reported for these women. The H-2-CLA isomers were metabolically different. The relative percent differences between the accumulation of 9c,11t-18:2-d(6) and 10t,12c-18:2-d(4) in plasma lipid classes ranged from 9 to 73%. The largest differences were a fourfold higher incorporation of 10t,12c-18:2-d(4) than 9c,11t-18:2-d(6) in 1-acyl PC and a two- to threefold higher incorporation of 9c,11t-18:2-d(6) than 10t,12c-18:2-d(4) in cholesterol esters. Compared to 9c- 18:1-d8 and 9c,12c-18.2-d(2), the 10t,12c-18:2-d(4) and 9c,11t-18:2-d(6) isomers were 20-25% less well absorbed. Relative to 9c-18:1, incorporation of the CLA isomers into 2-acyl PC and cholesterol ester was 39-84% lower and incorporation of 10t,12c-18:2 was 50% higher in 1-acyl PC. This pattern of selective incorporation and discrimination is similar to the pattern generally observed for trans and cis 18:1 positional isomers. Elongated and desaturated CLA metabolites were detected. The concentration of 6c,10t,12c-18:3-d(4) in plasma TG was equal to 6.8% of the 10t,12c-18:2-d(4) present, and TG was the only lipid fraction that contained a CLA metabolite present at concentrations sufficient for reliable quantification. In conclusion, no effect of dietary CLA was observed, absorption of CLA was less than that of 9c-18:1, CLA positional isomers were metabolically different, and conversion of CLA isomers to desaturated and elongated metabolites was low.