To determine the effect of foods with added fiber on blood urea nitrogen (BUN) and serum creatinine concentrations in patients with chronic kidney disease (CKD). Participants were enrolled in a 6-week single-blind crossover study. Free living with partial dietary intervention. Thirteen CKD patients with Modification of Diet in Renal Disease formula-based estimated glomerular filtration rate (eGFR) ≤50 mL/minute/1.73 m(2) at the time of screening (5 men, 8 women; mean age, 67.0 ± 14.8 years) completed the study. Patients consumed control foods (cereal, cookies, and bars) providing 1.6 g/day fiber daily for 2 weeks, followed by similar foods providing 23 g/day fiber daily for 4 weeks, incorporated into their usual diets. The main outcome of the study was the determination of the impact of foods with added fiber on BUN and serum creatinine levels. Consuming foods with added fiber resulted in a 10.6% decrease in mean BUN concentration (13.8 ± 2.0 to 12.1 ± 1.8 mmol/L or 38.5 ± 5.6 to 34.0 ± 5.1 mg/dL; P < .05). Serum creatinine level decreased from a baseline value of 216 ± 26 to 201 ± 23 mmol/L (2.44 ± 0.30 to 2.27 ± 0.26 mg/dL; P < .05) after 2 weeks of fiber-containing food consumption, and remained significantly lower at 195 ± 23 mmol/L (2.21 ± 0.26 mg/dL) after 4 weeks of the intervention (P < .05). Calculated eGFR increased from a baseline value of 29.6 ± 3.5 to 31.4 ± 3.8 mL/minute/1.73 m(2) at the end of 2 weeks, and remained higher at 32.5 ± 3.6 mL/minute/1.73 m(2) after 4 weeks of fiber intervention (P < .05). We conclude that increasing fiber intake in CKD patients through the consumption of foods with added fiber may reduce serum creatinine levels and improve eGFR. Additional studies are warranted to confirm these findings and to determine whether the changes are due to direct effects on kidney function. Copyright © 2013 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.