Phosphorus Additives and Albuminuria in Early Stages of CKD: A Randomized Controlled Trial

Background Little is known about the effects of phosphorus additives on patients with kidney disease. Study Design Randomized, double-blind, crossover trial. Setting & Participants 31 adults with early stages of presumed chronic kidney disease (estimated glomerular filtration rate ≥ 45 mL/min/1.73 m²; urine albumin-creatinine ratio sex-specific cutoff points: men ≥ 17 mg/g, women ≥ 25 mg/g). Intervention Higher versus lower phosphorus intake for 3 weeks. Higher phosphorus intake was achieved by the addition of commercially available diet beverages and breakfast bars to diet. Outcomes Change in 24-hour urine albumin excretion and plasma fibroblast growth factor 23 level. Measurements Two 24-hour urine collections and a single fasting blood draw at the end of each period. Results Mean baseline values for phosphorus intake, 24-hour urine phosphorus excretion, and estimated glomerular filtration rate were 1,113 ± 549 (SD) mg/d, 688 ± 300 mg/d, and 74.6 ± 22.0 mL/min/1.73 m². Median urine albumin excretion of 82.7 (IQR, 39.6-174.1) mg/d. Although phosphorus intake from study products increased by 993 mg/d (P < 0.001) during the higher compared to lower phosphorus additive period, background phosphorus intake decreased by 151 mg/d (P = 0.004). Higher phosphorus additive consumption increased 24-hour urine phosphorus excretion by 505 (95% CI, 381 to 629) mg/d (P < 0.001), but did not significantly increase albuminuria (higher vs lower: 14.3%; 95% CI, −2.5% to 34.0%; P = 0.1) or fibroblast growth factor 23 level (higher vs lower: 3.4%; 95% CI, −5.9% to 13.6%; P = 0.4). Limitations Small sample size, short duration of intervention, changes in background diet during the intervention. Conclusions A 3-week consumption of higher phosphorus food additives did not significantly increase albuminuria. Further studies are needed to confirm these results.