Carbohydrates are the largest component of a typical poultry diet and, potentially, the least understood nutrients, especially dietary fiber (DF). Therefore, a series of 4 experiments was conducted to determine the main role of DF in the entire nutrient metabolism in broiler chickens. The first experiment (chapter 3) utilized increasing levels of cellulose and soyhulls as sources of dietary fiber to achieve 4, 6, and 8% crude fiber (CF). Soyhulls had a more substantial impact improving intestinal histomorphology and performance parameters compared to cellulose when added at 4% CF. The second experiment (chapter 4) attempted to replicate different soluble (SF) to insoluble fiber (IF) ratios using semi-purified diets. It was clearly observed that higher soluble to insoluble fiber ratios interfere with normal nutrient digestibility and increase intestinal viscosity and that replacement of SF with IF recovers performance parameters and nutrient digestibility. To better understand the role of physical structure of dietary fiber, the third experiment (chapter 5) investigated the use of diets varying in fiber type, particle size, and inclusion level, yet maintaining the same nutrient levels. Among fiber-containing treatments, weight gain was better for soyhull-containing diets with a fine particle and lower inclusion level (i.e. 4%). Coarse particles of soyhulls increased gizzard relative weight. The fourth experiment (chapter 6) utilized pelleted diets and two sources of soybean meal, namely, the typical 48% crude protein soybean meal and the hulled 44% crude protein soybean meal to which soyhulls were added. Results from this experiment indicate that inclusion of hulled 44% soybean meal can positively modulate intestinal histomorphology parameters and expression of immune genes without compromising performance. Altogether, these results indicated that dietary fiber is an important dietary component modulating nutrient metabolism and general physiology in broiler chickens. Based on the results from these experiments it is concluded that soybean hulls can be added to diets of broiler chickens at a maximum level of 6%. Future research should strive to stablish the adequate inclusion level of other fibrous ingredients in order to develop practical and cheaper diets aimed at reducing the production costs in the broiler industry.