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The metabolism of c9,t11-conjugated linoleic acid (CLA) in humans was investigated by oral administration of the test item to 36 healthy human volunteers at concentrations of 0.8, 1.6 or 3.2 g/d CLA for two months (Mele et al., 2013).

The plasma concentration of c9,t11 CLA increased linearly 3-, 6- and 11-fold, with respect to unsupplemented controls, following dietary supplementation with 0.8, 1.6 or 3.2 g/d of CLA intake, respectively. The metabolites of c9,t11 CLA after delta 6 desaturation (CD 18:3) increased 1.5-, 2- and 4- fold with respect to unsupplemented controls, while CD 20:3 reached a plateau at 4-fold increase after 1.6 g/d CLA intake. The peroxisomal beta oxidation product, CD 16:2, increased of 1.5-, 2- and -3 fold in plasma. The ratio between the plasma value of CD 16:2 and CLA which indicates the peroxisomal beta oxidation ratio, decreased linearly up to 1.6 g/d CLA intake, and stabilised at this level of CLA intake. CLA supplementation between 0.8 and 3.2 g/d did not cause any significant changes in plasma cholesterol levels. After two months wash out period, plasma levels of CLA returned to basal levels, for all levels of dietary CLA supplementation.

The safety of CLA was additionally assessed in a 24 month oral repeated dose study in healthy overweight volunteers (male/female) (Gaullier et al., 2005). The age of the 157 volunteers ranged from 18 to 65 years. Their BMI was between 25 and 30 kg/m². All participants were supplemented with 3.4 g CLA/d in the triglyceride form. No treatment related adverse effects were recorded.