The ever high feed costs in swine production contribute to the largest variable expense for today’s producers. Due to this fact, research has focused on increasing feed efficiency. In this study, residual feed intake (RFI) was utilized as a measure of feed efficiency in lines of purebred Yorkshire pigs that were selected for increased and decreased feed efficiency on a standard corn-soybean diet that was high in energy and low in fiber (control diet). The low RFI (LRFI) line was selected for increased feed efficiency while the high RFI (HRFI) line was selected for reduced feed efficiency. In generations 8 and 9, the low and high RFI lines were challenged with a low energy, high fiber diet (LEHF). This diet reflects the addition of alternative feed stuffs to swine diets in commercial settings in order to decrease feed costs. Results indicate that the difference in feed efficiency between the two lines was substantially lower when fed the LEHF diet compared to the control diet. Thus, when pigs are fed diets with substantial byproducts, it is important that pigs are also selected for efficiency under such diets.