Effect of Conjugated Linoleic Acid as a Supplement or Enrichment in Foods on Blood Glucose and Waist Circumference in Humans: A Metaanalysis

Background: Controversy persists regarding the effect of mixtures of conjugated linoleic acids (c9, t11- and t10, c12-CLA) in fasting blood glucose (FBG) and waist circumference (WC) in humans. Objective: The aim of this meta-analysis is to explore the effect of CLA on FBG and WC. Method: PubMed, Google Scholar, Cochrane Library, Science Direct, Pro-Quest and Ovid were searched up to January 2015. Studies that examined the effect of CLA supplementation or foods enriched with CLA on FBG and WC in healthy adults were included. Studies in animals or unhealthy individuals and studies other than clinical trials were excluded. Of the 3,095 articles initially retrieved, 32 eligible randomized clinical trials were included in this systematic review. The mean difference and standard deviation of changes in FBG and WC in the intervention and control groups were used as effect size measures for the meta-analysis. Results: Subgroup analysis showed that CLA supplement consumption did not significantly influence FBG (standardized mean differences [SMD] = 0.075 mg/dL; 95% confidence interval (CI) = −0.099 to 0.249; p = 0.399) or WC (SMD = -0.149 cm; 95% CI = −0.522 to 0.225; p = 0.435). Foods enriched in CLA also showed no significant effect on FBG (SMD = 0.126 mg/dL; 95% CI = −0.100 to 0.352; p = 0.274) or WC (SMD = -0.233 cm; 95% CI = −0.625 to 0.159; p = 0.244). Conclusion: We conclude that c9, t11- and t10, c12-CLA administered as a supplement or used to enrich foods does not affect FBG or WC in humans.