Following an application from BASF SE and Stepan Lipid Nutrition, submitted for the authorisation of a health claim pursuant to Article 13(5) of Regulation (EC) No 1924/2006 via the Competent Authority of the Netherlands, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver an opinion on the scientific substantiation of a health claim related to an equimolar mixture (marketed under the trade names Clarinol® and Tonalin®) of the two conjugated linoleic acid (CLA) isomers c9,t11 and t10,c12. The Panel considers that the food is sufficiently characterised. The claimed effect is “contributes to a reduction in body fat mass”. In previous assessments on the safety of these equimolar isomeric mixtures of CLA, the NDA Panel considered that the observed increase in plasma and urinary concentrations of isoprostanes, which may indicate an increase in lipid peroxidation, and the increase in some markers of subclinical inflammation associated with CLA consumption, together with the limited data available on the effects of CLA on vascular function, may indicate a potential for vascular damage in the longer term. The Panel considers that the information provided does not establish that a reduction in body fat mass, when accompanied by an increase in markers of lipid peroxidation and inflammation, is a beneficial physiological effect for the target population. The Panel concludes that a cause and effect relationship has not been established between the consumption of an equimolar mixture of the CLA isomers c9,t11 and t10,c12, marketed under the trade names of Clarinol® and Tonalin®, and a beneficial physiological effect.