Association of conjugated linoleic acid consumption and liver enzymes in human studies: A systematic review and meta-analysis of randomized controlled clinical trials

Abstract

Objective: The aim of this study was to systematically review the association of conjugated linoleic acid (CLA) consumption in two forms of foods enriched or supplemented with CIA on serum liver enzymes in human studies. Methods: We searched PubMed, Google Scholar, Cochrane Library, ScienceDirect, ProQuest, and Ovid up to January 2015. Studies that examined the effect of CIA supplementation or foods enriched with CIA on liver enzymes concentrations among healthy adults were included. The mean difference and SD of changes in serum liver enzymes between the intervention and control groups were used as effect size for the meta-analysis. Results: The analysis demonstrated that CIA supplementation led to slight and nonsignificant decreases in alkaline phosphatase (ALP) levels (mean difference MD -0.216; 95% confidence interval CI, -0.60 to 0.17; P = 0.28). CIA intake can nonsignificantly increase alanine transaminase (ALT) levels (MD = 0.107 U/L; 95% CI,-0.29 to 0.244; P = 0.124) and can significantly increase aspartate aminotransferase (AST) levels (MD = 0.171 U/L; 95% CI, 0.034-0.307; P = 0.01). Subgroup analysis based on CIA source showed that CIA supplementation or foods enriched with CIA did not significantly alter ALT levels. Subgroup analysis showed that CIA supplementation led to significant increases in AST levels (MD = 0.224 U/L; 95% CI, 0.071-0.376; P = 0.004). However, foods enriched with CIA did not have any significant effects on AST levels. Conclusion: CIA supplementation was associated with a significantly increased circulating AST without any significant effect on ALP and ALT levels. Prospective studies are necessary to assess the clinical outcomes of the association between CIA and liver enzyme concentrations. (C) 2016 Elsevier Inc. All rights reserved.