(P18-035-24) Dietary Fiber Fermentability and Viscosity Impact Phosphorus Homeostasis and Urinary Phosphorus Excretion in a Rat Model of Chronic Kidney Disease

Objectives: Hyperphosphatemia is a key driver of the pathogenesis of chronic kidney disease (CKD)-mineral and bone disorder. Current therapies include lowering dietary phosphorus and intestinal phosphate binders. However, despite these recommendations, phosphorus concentrations in people with kidney failure remain high. Therefore, innovative therapies are needed. We tested the hypothesis that dietary fiber supplementation impacts phosphorus homeostasis and urinary phosphorus excretion based on their fermentability and viscosity properties.

Methods: 22-week-old Cy/+ male rats (~50% kidney function compared to normal; CKD hereafter) were randomly assigned to receive one of four fiber treatments (10% w/w each) based on fermentability and viscosity: 1) Cellulose (-fermentability, -viscosity), 2) Inulin (+fermentability, -viscosity), 3) Psyllium husk (-fermentability, +viscosity), or 4) Pectin (+ fermentability, +viscosity). Diets were semi-purified, casein-based with 0.7% calcium and phosphorus. Treatments lasted 10 wks, and rats were euthanized at 32 wks of age (kidney failure; ~15% of normal). During the last week of the study, rats were placed in metabolic cages for 3 days for urine collection. Serum creatinine, plasma phosphorus, and urinary phosphorus and creatinine were analyzed using colorimetric assays. One-way ANOVA was used to test the effect of dietary fiber types on outcome measures.

Results: After 10 wks of treatment, inulin, psyllium, pectin-treated CKD rats had lower serum creatinine concentration compared to cellulose, which served as negative control (p < 0.04). Treatment with viscous fibers including psyllium and pectin resulted in lower plasma phosphorus (p < 0.02), curbing its steady increase over time as opposed to cellulose. This aligned with a lower tubular reabsorption of phosphorus (p < 0.02) and fractional excretion of phosphorus trending towards significance (P=0.06), suggesting that viscous fibers impede intestinal phosphorus absorption.

Conclusions: The incorporation of fermentable and viscous fiber into the diet of CKD rats resulted in alterations in phosphorus homeostasis and urinary excretion suggesting that dietary fiber may be an innovative therapy for phosphorus management in CKD.

Funding Sources: AB was supported by KL2/K12 (KL2TR002530, UL1TR002529, and K12TR004415) and the Showalter Trust.