Effects of Lowering Dietary Phosphorus Additive Intake on Mineral Metabolism in Adults with and without CKD

Key Points Lowering phosphorus additive intake reduces fibroblast growth factor 23 concentrations in adults with and without CKD. Lowering phosphorus additive intake reduced fibroblast growth factor 23 in White but not in Black healthy individuals. Lowering phosphorus additive intake reduces circulating parathyroid hormone concentrations in individuals with CKD. Background Excess phosphorus additive intake leads to alterations in phosphorus metabolism that are linked to cardiovascular and kidney disease. The effects of lowering phosphorus additive intake in adults with and without CKD are unclear. Methods We conducted a feeding study in 39 adults without and 11 adults with CKD. Participants were fed a phosphorus additive-enhanced diet for 2 weeks followed by a low additive diet for 6 weeks. Both diets were identical except for phosphorus additive content. Blood and urine samples were collected at regular intervals with analyses comparing follow-up measures of mineral metabolism markers to baseline values. Results The mean (SD) age of the non-CKD group was 34 (12) years, among whom 51% were male, 36% were of Black race, and the mean (SD) eGFR was 106 (16) ml/min per 1.73 m 2 . The mean (SD) age of the CKD group was 72 (6) years, among whom 36% were male, 82% were of Black race, and the mean (SD) eGFR was 35 (13) ml/min per 1.73 m 2 . After consuming the additive-enhanced diet for 2 weeks, consuming the low additive diet for 6 weeks decreased 24-hour urine phosphorus excretion by approximately 30% in both groups. In the non-CKD group, the effect of the low additive diet on circulating fibroblast growth factor 23 (FGF23) concentrations differed by race ( P interaction = 0.03)—FGF23 decreased by 22% from baseline in White adults ( P < 0.001) but not in Black adults ( P = 0.08). In the CKD group, FGF23 decreased 25% after 6 weeks of the low additive diet ( P < 0.001) with no difference by race. Intact parathyroid hormone concentrations decreased 20% in CKD participants and did not change in the non-CKD participants. Conclusions Six weeks of a low phosphorus additive diet decreased FGF23 and parathyroid hormone in adults with moderate CKD. Lowering phosphorus additive intake lowered FGF23 in White adults without CKD but had no effect in Black adults without CKD. Clinical Trial registry name and registration number: NCT02620449.