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 .
An oil mixture with trans-10, cis-12 conjugated linoleic acid increases markers of inflammation and in vivo lipid peroxidation compared with cis-9, trans-11 conjugated linoleic acid in postmenopausal women.
A mixture of trans-10 , cis-12 ( t10,c12 ) and cis-9 , trans-11 ( c9,t11 ) conjugated linoleic acid ( CLA mixture ) reduced atherosclerosis in animals , thus the effect of these isomers on endothelial dysfunctions leading to inflammation and atherosclerosis is of interest . We gave 75 healthy postmenopausal women a daily supplement of 5.5 g of oil rich in either CLA mixture , an oil rich in the naturally occurring c9,t11 CLA ( CLA milk ) , respectively , or olive oil for 16 wk in a double-blind , r and omized , parallel intervention study . We sample d blood and urine before and after the intervention . The ratios of total cholesterol : HDL cholesterol and concentrations of C-reactive protein , fibrinogen , and plasminogen activator inhibitor-1 were significantly higher in women supplemented with the CLA mixture than in those supplemented with CLA milk .  Plasma triacylglycerol was significantly higher and HDL cholesterol was lower in women supplemented with the CLA mixture than with olive oil . Both CLA supplements increased lipid peroxidation , a marker of in vivo oxidative stress measured as urinary free 8-iso-prostagl and in F(2alpha ) . However , the CLA mixture increased lipid peroxidation more than the CLA milk did . The plasma cytokines interleukin-6 and tumor necrosis factor-alpha were not affected by the treatments , nor were any of the other variables measured . In conclusion , oil containing trans-10,cis-12 CLA has several adverse effects on classical and novel markers of coronary vascular disease , whereas the c9,t11 CLA isomer is more neutral , except for a small but significant increase in lipid peroxidation compared with olive oil
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 .