Background: Dietary conjugated linoleic acid (CLA) represents a group of positional and geometric isomers of conjugated dienoic derivatives of linoleic acid. The effects of dietary CLA on blood lipids and body composition in humans remain controversial.
Objective: To examine whether consumption of milk enriched naturally or synthetically with cis 9, trans 11 (c-9, t-11) and trans 10, cis 12 (t-10, c-12) CLA isomers alters blood lipid indices, including concentrations of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triacyglycerol; indices of liver function including plasma alanine transaminase and total bilirubin; C-reactive protein; tumor necrosis factor-alpha; and body weight and composition in moderately overweight, borderline hyperlipidemic humans.
Design: A randomized, 3-phase, crossover, single-blind clinical trial was carried out in moderately overweight, borderline hyperlipidemic individuals who consumed (1) milk naturally enriched in CLA (4.2%) containing c-9, t-11 only providing 1.3 g/d of CLA; (2) milk enriched with a 4.2% synthetic mixture of t-10, c-12 and c-9, t-11 CLA isomers providing 1.3 g/d of CLA; or (3) untreated milk as a control providing 0.2 g/d CLA. Dietary phases were each 8 weeks in duration and were separated by 4-week washout periods. Plasma lipid levels were measured in blood samples collected at the beginning and end of each dietary phase. Magnetic resonance imaging was carried out at the beginning and end of each dietary phase to assess any changes in regional body fat composition.
Results: Compared with the control intervention, consumption of the two CLA-enriched milks failed to alter plasma total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, or triacyglycerol concentrations; body weight; or fat composition. CLA consumption did not significantly affect plasma alanine transaminase, total bilirubin, C-reactive protein, or tumor necrosis factor-alpha concentrations.
Conclusion: Results from this study fail to support the role of milk enriched naturally with CLA containing c-9, t-11 or synthetically with c-9, t-11 and t-10, c-12 CLA isomers in modulation of lipid profiles or body composition in moderately overweight, borderline hyperlipidemic individuals.