The lymphatic absorption of a structured triacylglycerol vs an equivalent physical mixture of the constituent medium-chain triacylglycerol and fish oils was studied. Each of four canines served as its own control in a crossover feeding design with the investigators unaware of diet contents. Lymphatic absorption of n-3 and medium-chain fatty acids peaked within 4-8 h of feeding either diet. The lymph contained more 10:0 fatty acids than 8:0 despite an overall ratio of 10:0 to 8:0 of 0.3 for the diets. The mass of medium-chain fatty acids absorbed in the lymph at measured time points was 2.6 +/- 0.5-fold higher (mean +/- SE of 12 determinations) for the structured triacylglycerol compared with the physical mix. Molecular species analyses revealed that the medium-chain fatty acids in lymph were present as mixed triacylglycerols. The unique molecular structure of these mixed triacylglycerols and the fatty acids at the 2-position may account for the improved absorption.