The Effect of Dietary Phosphorus Restriction on Urine Protein Excretion in Patients With Proteinuria: A Randomized Controlled Trial

The present study was designed to determine the effect of dietary phosphorus restriction, independent of protein intake, on the urinary protein excretion in patients with proteinuria.Seventy-one patients with proteinuria were enrolled in a parallel randomized controlled trial study. The patients were randomly allocated to receive either a recommended phosphorus-restricted diet (n = 36) or a recommended control diet (n = 35), for 8 weeks. A diet was designed and recommended to participants in a way that both trial groups would receive the same amount of energy and protein and the only significant difference between them was the amount of phosphorus intake. The study outcomes included the changes in spot urine protein-to-creatinine ratio, the changes in serum and urine levels of phosphorus, as well as the changes in estimated glomerular filtration rate (eGFR).The mean ± standard deviation of age, body mass index, and eGFR of the participants were 59 ± 14 years, 29 ± 5.5 kg/m2, and 56.1 ± 21.7 mL/min/1.73 m2, respectively. The amount of phosphorus intake decreased significantly in the phosphorus-restricted group compared to the control one (-709 vs. -369 mg/day; P < .001). This decrease is accompanied by a significant reduction in urine protein-to-creatinine ratio in the phosphorus-restricted group; however, this change did not reach a significant level when compared to the control one (the mean change: -75.78 vs. -55.25 mg/g; P = .539). Limiting the phosphorus intake did not change its serum and urine values as well as eGFR at the end of the trial.Although adherence to a phosphorus-restricted diet by patients with proteinuria led to a significant decrease in urinary protein excretion, this change was not significantly different from that of the control diet. Further studies with larger sample sizes and different designs will reveal more evidence for a link between phosphorus intake and proteinuria.