The aim of the study is to look at the effects of dietary phosphorus on phosphorous and calcium whole-body balance and kinetics in moderate chronic kidney disease (CKD). N = 14 enrolled subjects will be randomly assigned to a cross-over order of (A) Low P Diet, High P Diet. Each cross-over phase will be 19 days and consist of a 7-day outpatient, controlled diet period, followed by a 5- day inpatient, controlled diet, balance, and kinetic study period, followed by a second 7-day outpatient, controlled diet period.
Men or women, ages 30-75 years old, any race or ethnicity
Moderate CKD, defined by KDIGO as eGFR category 3b (30-44 mL/min) or 4 (16-29 mL/min) with albuminuria categories A1-A3
Serum intact parathyroid hormone above assay normal limit
Female subjects must be postmenopausal (>12 months since last menstrual period), surgically sterile, or confirmed not pregnant by pregnancy test
Willing to discontinue supplements (e.g., vitamin D, calcium, multivitamin/minerals, or others) upon enrollment until completion of the study
Adequate vitamin D status defined as serum 25D > 20 ng/mL based on National Academy of Medicine (then Institute of Medicine) criteria.
Plans to initiate dialysis within 6 months
Hypercalcemia defined as corrected serum calcium >9.8 mg/dL within past 3 months
Crossover
LP then HP
Other interventionCross-over order of LP then HP diet. Each cross-over phase will be 19 days and consist of a 7-day outpatient, controlled diet period, followed by a 5-day inpatient, controlled diet, balance, and kinetic study period, followed by a second 7-day outpatient, controlled diet period.
HP then LP
Other interventionCross-over order of HP then LP diet. Each cross-over phase will be 19 days and consist of a 7-day outpatient, controlled diet period, followed by a 5-day inpatient, controlled diet, balance, and kinetic study period, followed by a second 7-day outpatient, controlled diet period.
Phosphorus Balance
Determined by analysis of phosphorus content in complete 24-hour urine and stool collections, subtracted from the diet phosphorus content consumed
Calcium Balance
Determined by analysis of calcium content in complete 24-hour urine and stool collections, subtracted from the diet calcium content consumed
Fractional phosphorus absorption
Determined by kinetic modeling of serum, urine, and stool P-33 isotope after oral and IV isotope administrations
Bone phosphorus balance
Determined by kinetic modeling of serum, urine, and stool P-33 isotope after oral and IV isotope administrations
Bone calcium balance
Determined from the natural stable isotope ratio of 44-Ca to 42-Ca in serum and urine
Urine phosphorus
Determined from the 24-hour urine collections over 1 week (daily average)
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University of Minnesota
Lead sponsor
Indiana University
Collaborator
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