Effect of conjugated linoleic acid on blood inflammatory markers: a systematic review and meta-analysis on randomized controlled trials

Abstract

Background/objectives Conjugated linoleic acid (CLA) is a polyunsaturated fatty acid with attractive biological activities. Numerous studies have been conducted on the inflammation-lowering effects of CLA in in vitro and animal models. However, the effects of CLA treatment on the inflammatory markers in humans are controversial. Therefore, the objective of this study was to perform a systematic review and meta-analysis on controlled clinical trials (RCT) assessing the effects of CLA supplementation on the circulating inflammatory markers, including C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). Subjects/methods The literature search of RCTs was performed using Pubmed/Medline, Scopus, ScienceDirect, Web of science, Cochrane, and Google Scholar databases from inception to March 2017. Weighted mean differences were estimated and the pooled effect size was calculated by a random effects model. Results Of the 427 identified studies, eleven RCTs, including 420 subjects were included in the statistical analysis. Findings suggested that CLA supplementation increased blood levels of CRP by 0.89 mg/l (95 CI: 0.11, 1.68; P = 0.025) and TNF-alpha levels by 0.39 pg/ml (95 CI: 0.23, 0.55; P < 0.0001). However, blood IL-6 levels were marginally decreased by 0.32 pg/ml (95 CI: -0.71, 0.07; P = 0.11) following CLA supplementation. There was a significant heterogeneity for the impact of CLA on CRP and IL-6, but not TNF-alpha. Conclusions This meta-analysis showed that CLA supplementation may increase inflammatory markers (CRP and TNF-alpha). There are concerns about using CLA supplementation as an anti-obesity agent among the obese population for at least a short duration.