There was a significant heterogeneity for the impact of CLA  on CRP and IL-6 , but not TNF-α .
Conclusions This meta- analysis showed that CLA supplementation may increase inflammatory markers ( CRP and TNF-α ) .
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 .
Conjugated linoleic acid induces lipid peroxidation in humans
Conjugated linoleic acid ( CLA ) is shown to have chemoprotective properties in various experimental cancer models . CLA is easily oxidised and it has been suggested that an increased lipid oxidation may contribute to the antitumorigenic effects . This report investigates the urinary levels of 8‐iso‐PGF2α , a major isoprostane and 15‐keto‐dihydro‐PGF2α , a major metabolite of PGF2α , as indicators of non‐enzymatic and enzymatic lipid peroxidation after dietary supplementation of CLA in healthy human subjects for 3 months . A significant increase of both 8‐iso‐PGF2α and 15‐keto‐dihydro‐PGF2α in urine was observed after 3 months of daily CLA intake ( 4.2 g/day ) as compared to the control group ( P<0.0001 ) . Conjugated linoleic acid had no effect on the serum α‐tocopherol levels . However , γ‐tocopherol levels in the serum increased significantly ( P=0.015 ) in the CLA‐treated group . Thus , CLA may induce both non‐enzymatic and enzymatic lipid peroxidation in vivo . Further studies of the mechanism behind , and the possible consequences of , the increased lipid peroxidation after CLA supplementation are urgently needed
There was a significant heterogeneity for the impact of CLA  on CRP and IL-6 , but not TNF-α .
Conclusions This meta- analysis showed that CLA supplementation may increase inflammatory markers ( CRP and TNF-α ) .
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 .