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

•Conjugated linoleic acid (CLA) supplement or foods enriched with CLA did not significantly alter alanine transaminase levels.•CLA supplementation led to a significant increase in aspartate aminotransferase levels.•CLA supplementation did not significantly alter alkaline phosphatase levels.

ObjectiveThe 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 CLA on serum liver enzymes in human studies.MethodsWe searched PubMed, Google Scholar, Cochrane Library, ScienceDirect, ProQuest, and Ovid up to January 2015. Studies that examined the effect of CLA supplementation or foods enriched with CLA 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.ResultsThe analysis demonstrated that CLA 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). CLA 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 CLA source showed that CLA supplementation or foods enriched with CLA did not significantly alter ALT levels. Subgroup analysis showed that CLA 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 CLA did not have any significant effects on AST levels.ConclusionCLA 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 CLA and liver enzyme concentrations.