The present study was performed to evaluate the effects of dietary energy source (starch vs fat) and of increased levels of dietary energy and essential amino acids (EAA), related to the assumed increased EAA and energy requirements in immune stimulated pigs, on the growth performance of growing-finishing (GF) pigs under low sanitary conditions (LSC), in which the immune system of the pigs was activated, or under high sanitary conditions (HSC) resulting in a lower state of activation of the immune system. The trial was conducted with 408 male pigs (Tempo boar x (York x Dutch Landrace) sow) during the weaner, grower and finisher phase. Piglets were weaned at an age of four weeks and followed till delivery to the slaughterhouse. In a 2 × 2 × 2 factorial design, pigs were allocated to either high sanitary conditions (HSC) or low sanitary conditions (LSC). A contrast in sanitary conditions was generated by imposing to the pigs differences in strategy for vaccination against pathogens, cleaning and hygiene protocol, antibiotic treatment and deworming. During the growing and finishing period, pigs had ad libitum access to one of four experimental diets, a diet with starch as main energy source or a diet with fat and starch as main energy source, each diet having either basal energy and EAA concentrations (B diet) or increased concentrations in energy and EAA (I diet). The levels of supplementation of EAA and energy in the I diets compared to the B diets were based on a model that calculated the effects of low sanitary conditions on the EAA and energy requirements of pigs. At an age of nine weeks, pigs were moved to the rooms for GF pigs. The HSC GF pigs were fed a starter diet during the first five weeks, followed by a grower diet for four weeks and then a finisher diet till delivery to the slaughterhouse. The LSC GF pigs were fed a starter diet during six weeks, followed by a grower diet for four weeks and then a finisher diet till delivery to the slaughterhouse. In all pens, 8 or 9 GF pigs were housed.