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

Abstract

Background Little is known about the effects of phosphorus additives on patients with kidney disease. Study Design Randomized, double-blind, cross-over trial Setting & Participants 31 adults with early stages of presumed chronic kidney disease (estimated glomerular filtration rate [eGFR] ≥ 45 ml/min/1.73m2; urine albumin-creatinine ratio [ACR] sex-specific cut points: men ≥ 17 mg/g, women ≥ 25 mg/g). Intervention Higher vs lower phosphorus intake for 3 weeks. Higher phosphorus intake was achieved by 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 Measurements Two 24-hour urine collections and a single fasting blood draw at the end of each period. Results Mean baseline values of phosphorus intake, 24-hour urine phosphorus excretion, and eGFR were 1113 ± 549 (SD) mg/d, 688 ± 300 mg/d, and 74.6 ± 22.0 ml/min/1.73m2. Median albuminuria was 82.7 (IQR, 39.6–174.1) mg/d. While 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, 381–629) 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 (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.

Nutritional treatment of advanced CKD: twenty consensus statements

“…In fact, under normal physiological conditions, a healthy kidney is able to regulate urinary secretions of phosphates with food intake, but the progressive loss of glomerular filtrate, due to CKD progression, rationalizes a reduction of phosphorus intake to below 700 mg/die, the recommended level for the general adult population [ 36 ]. Surely, it is useful to educate patients to avoid consuming “hidden” phosphates through additives found in preserved foods or soft drinks [ 38 , 39 ]. Choosing foods with a lower phosphorus content and using foods of plant origin is useful in limiting the net phosphorus load [ 40 ].…”

Dietary Phosphorus Intake and the Kidney

“…However, the effect of phosphorus intake on FGF23 appears to be modest in human studies, with some studies unable to detect a significant effect (19, 32, 48, 78, 79, 94, 111, 161, 165). Recent human studies suggest that PTH rather than FGF23 explains the increased phosphaturia that occurs immediately after an acute phosphorus load (137).…”

“…Chang et al (32) recently conducted a randomized, crossover study examining the effects of phosphorus additives on urinary albumin excretion in 31 patients with eGFR ≥45 mL/min/1.73 m 2 and albuminuria. Participants received unaltered, commercially available diet beverages and breakfast bars with and without phosphorus additives to produce a contrast of 998 mg/d of dietary phosphorus and 505 mg/d in 24-h urine phosphorus excretion between periods.…”

Association between Dietary Mineral Intake and Chronic Kidney Disease: The Health Examinees (HEXA) Study

“…The biggest reason between the former studies [23,24,25] and the latter studies [13], including our study, is that the former studies [23,24,25] have shown that phosphorous intake is associated with the risk of ESRD exacerbations and death in most of the patients with stage 3 or higher CKD; whereas the latter studies have shown that phosphorous intake is associated with the likelihood of CKD morbidity in the general population, where CKD patients with three or more stages are less common (about 25% [mean age = 65 years] or 15% [mean age = 66 years] in two Italian studies [13] and only 1.8% in the Korean population [this study]). Due to the complex interaction between FGF23 [26], phosphorus metabolism [9], and CKD progression [27], further studies exploring the relationship between dietary phosphorus and CKD are needed.…”