Effects of Lowering Dietary Phosphorus Additive Intake on Mineral Metabolism in Adults with and without Chronic Kidney Disease.

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 chronic kidney disease (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 two weeks followed by a low additive diet for six 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 mean (SD) eGFR was 106(16) ml/min/1.73m2. The mean (SD) age of the CKD group was 72(6) years, among whom 36% were male, 82% were of Black race, and mean (SD) eGFR was 35(13) ml/min/1.73m2. After consuming the additive-enhanced diet for two weeks, consuming the low additive diet for six weeks decreased 24-hour urine phosphorus excretion by ∼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 (Pinteraction=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 six weeks of the low additive diet (P<0.001) with no difference by race. Intact parathyroid hormone (PTH) concentrations decreased 20% in CKD participants and did not change in the non-CKD participants. CONCLUSION Six weeks of a low phosphorus additive diet decreased FGF23 and PTH 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.