In animal feed more and more co-products from human food production are used. These products are often rich in fiber and are relatively low in energy. To ensure sufficient energy concentration, diets are usually supplemented with fat when formulated with these fiber-rich products. The question arises whether these increased fat and fiber levels affect nutrient digestibility. Therefore, an experiment was designed to elucidate the effect of fat and fiber level and their interaction on nutrient digestibility and energy utilization in pig feed. A low fiber (LF, 34 g crude fiber/kg) and a high fiber (HF, 68 g crude fiber/kg) diet were formulated with a similar crude fat (CFAT) content (28 and 26 g/kg). Eight additional diets were formulated by adding 20 or 40 g/kg of either pig fat or soybean oil to each of the 2 basal diets resulting in a total of 10 experimental diets. Each diet was fed to 18 barrows (83.6 ± 8.9 kg) housed per 3 in 6 pens. The digestibility of organic matter (OM), crude protein (CP), CFAT, non-starch polysaccharides (NSP), neutral detergent fiber (NDF) and gross energy (GE) were derived from rectal spot sampling, using acid insoluble ash as marker. The net energy (NE) content was calculated according to the Dutch CVB system. More fiber reduced average daily feed intake (ADFI, P = 0.022) and tended to decrease average daily gain (ADG, P = 0.074), but gain:feed (G:F) was not affected (P > 0.05). Neither fat inclusion level nor fat type affected animal performance (P > 0.05). The NE content increased along with increasing fat level in the diet (P < 0.001), with an interaction between fat type/inclusion level and dietary fiber content (P < 0.001). In the HF diets the standardized digestibility of all nutrients was lower (P < 0.05) than in the LF diets, except for NDF. Higher fiber levels in the diet didn’t impact the digestibility of the added fat. The standardized CFAT digestibility of the HF diets with 20 and 40 g/kg fat/oil was higher than that of the non-fat supplemented diet (P < 0.05), whereas no significant differences in CFAT digestibility among the LF diets were observed (P > 0.05). The digestibility of the fat-free OM, NSP and NDF was affected (P < 0.05) by the fat type/inclusion level. Increasing fat level appeared to negatively affect the fat-free OM digestibility, in particular NDF. On the other hand, the negative effect of fat addition on digestibility and NE was relatively small in comparison to the extra energy added by the fat.