The effects of a designer fat as to changes in triacylglycerol structure in dietary fat on nutrient digestibility, nitrogen retention and fatty acid profile of plasma, erythrocyte membranes, liver, adipose tissue and skeletal muscle were examined in four groups of post-weaning piglets. The test fats added by 10% (w/w) to the diets were: R1 regiospecific structured fats with decanoic acid mainly located in the sn-1/3 positions and a long-chain fatty acid from rapeseed oil in the sn-2 position, R2 similar fat subjected to chemical randomization, R3 physical mixture of tridecanoin and rapeseed oil, and R4 rapeseed oil. The piglets were weaned at 28 days of age, and after one week of adaptation faeces and urine were collected quantitatively during three periods each of 7 days, in which the piglets were kept in metabolism cages for measurement of nutrient and energy digestibility and protein retention. Fat digestibility and nitrogen retention were improved significantly by feeding the manufactured oils containing 10:0 (R1-R3) compared to rapeseed oil (R4; P<0.05), with the highest improvement caused by the regiospecific oil (R1). The fatty acid profiles of plasma, erythrocyte membranes, liver, adipose tissue and skeletal muscle reflected the fatty acid profiles of the test fats, except for 10:0 which was only found in triacylglycerols in adipose tissue and blood plasma of R1-R3 in low concentrations, indicating that 10:0 was mainly oxidized providing energy for protein accretion.