In addition to the degree of saturation, the second major chemical variable that influences the dietary energy value of fats is the free fatty acid (FFA) content. Whilst it is appreciated that the digestible energy (DE) value of a hydrolysed fat (i.e. with a high FFA content) is lower than that of the same fat prior to hydrolysis, quantifying the response remains to be studied. Previous attempts to evaluate the effect of increasing FFA content have often been confounded with variability in degree of saturation. Accordingly it was the objective of the current study to examine the DE value of fats of varying FFA content but of constant degree of saturation.