Methods of treating diabetes in an animal and food compositions useful for treating diabetes are described. In one aspect of the invention, the method includes treating the animal with a therapeutically effective amount of CLA including 9,11-octadecadienoic acid and 10,12-octadecadienoic acid, isomers thereof, esters thereof, salts thereof or mixtures thereof. In another aspect of the invention, a food composition comprising a food product having a therapeutically effective amount of a purified CLA isomer, including cis,cis-9,11-octadecadienoic acid, trans,cis-10,12-octadecadienoic acid or a mixture of purified cis,trans-9,11-octadecadienoic acid and trans,cis-9,11-octadecadienoic acid is described.