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Abstract: TH-PO141

Effects of a Low Phosphorus Diet on Phosphorus and Calcium Whole-Body Balance and Intestinal Absorption: Results of a Pilot Study in Adults with Moderate CKD

Session Information

Category: Bone and Mineral Metabolism

  • 502 Bone and Mineral Metabolism: Clinical

Authors

  • Hill Gallant, Kathleen M., University of Minnesota Twin Cities, Minneapolis, Minnesota, United States
  • Wastney, Meryl E., Purdue University, West Lafayette, Indiana, United States
  • Zheng, Xinyuan, University of Minnesota Twin Cities, Minneapolis, Minnesota, United States
  • Moe, Sharon M., Indiana University School of Medicine, Indianapolis, Indiana, United States
  • Nachman, Patrick H., University of Minnesota Twin Cities, Minneapolis, Minnesota, United States
  • Cladis, Dennis, University of Minnesota Twin Cities, Minneapolis, Minnesota, United States
  • Biruete, Annabel, Purdue University, West Lafayette, Indiana, United States
  • Moorthi, Ranjani N., Indiana University School of Medicine, Indianapolis, Indiana, United States
Background

Dietary P restriction is often used as a management strategy to prevent and treat hyperphosphatemia and CKD-MBD progression. It is presumed that a low P diet results in lower P balance or retention, but this has not been determined, nor the effects on Ca absorption and balance.

Methods

This pilot two-phase crossover, controlled feeding, metabolic balance study investigated the effects of dietary P level (low P [LP], 800 mg/d; high P [HP], 1500 mg/d) on P and Ca balance and absorption in N=3 adults with moderate CKD. Nutrient content was similar, including low Ca (500 mg/d). Each phase consisted of 1wk run-in on the diet, 1wk inpatient metabolic balance, and 3wk washout between phases. Complete timed urine and feces were collected inpatient. Oral and IV Ca and P isotopes were administered and serial serum and urine samples analyzed for their concentrations to determine fractional intestinal absorption by kinetic modeling. Balance was calculated as intake minus urine and fecal excretion. Serum iPTH, iFGF, and 1,25D were measured at baseline and end of each phase.

Results

Intestinal fractional P absorption varied widely among participants (51-95%) but appeared unaffected by dietary P level in all participants. Thus, absolute intestinal P absorption (mg/d) was approximately doubled in the HP compared to the LP. 24h urine P was lower in all participants with the LP diet. The response in P balance to dietary P level varied among subjects. The response in fractional intestinal Ca absorption and Ca balance also varied. 24h urine Ca was very low in all subjects (6-20 mg/d) and did not change with the LP diet. Serum 1,25D was not associated with intestinal fractional P or Ca absorption nor in response to dietary P. iPTH and iFGF23 were lower with LP in two participants who had moderately elevated levels at baseline and with HP.

Conclusion

In adults with moderate CKD, Ca and P balance and intestinal absorption are variable in response to different controlled dietary P intakes. In this pilot study, fractional P absorption did not change with dietary P level and was not associated with 1,25D. Further studies are needed to identify explanatory factors for the observed variation in whole-body Ca and P physiology in adults with CKD.

Funding

  • NIDDK Support