Clinical Trial: Effect of Dietary Protein Source on Phosphaturia, PTH and FGF23 in Patients With CKD 3 and 4

Study Status: Completed
Recruit Status: Completed
Study Type: Interventional

Official Title: Effect of Dietary Protein Source on Phosphaturia, PTH and FGF23 in Patients With CKD 3 and 4

Brief Summary: Phosphorus is a substance in the blood that comes from food and is normally cleared from the body by the kidneys. In patients with kidney disease, excess phosphorus may build up in the body as you eat. This leads to problems with bones and blood vessels over time. In this study, we will compare the blood and urine before and after eating one week of a diet with a protein from plants (soy and grains) and before and after another one week of diet with protein from animals (meat and dairy products). The amount of phosphorus that the kidney puts out in the urine, and the changes in blood hormones in response to the diet will be measured at the beginning and end of each week on the two diets.

Detailed Summary:

Chronic Kidney Disease-Mineral Bone disorder (CKD-MBD) is a constellation of problems related to alterations in mineral and bone homeostasis that occur in CKD stage 3-5D (estimated GFR 60-15 ml/min). The damaged kidney is unable to fully excrete a phosphorus load, leading to a compensatory secondary hyperparathyroidism to attempt to increase urinary phosphorus excretion in order to maintain serum phosphorus in the normal range. Eventually this compensation of elevated PTH becomes pathologic and leads to abnormalities in biochemistries, bone and vascular disease, all of which are associated with morbidity and mortality in patients with CKD. Prevention of these complications is key to improved patient outcomes. Unfortunately, this normal or high normal phosphorus does not reflect the "behind the scenes" appropriate and inappropriate compensation. The use of medication to bind phosphorus from food (phosphate binders) may prevent absorption of phosphorus across the intestine and prevent or change the elevations in PTH and other hormones like FGF23. Thus, either urinary excretion of phosphorus, or changes in hormone may be more appropriate end points to evaluate efficacy of phosphate binders than is serum phosphorus.

In healthy individuals, there is variation throughout the day (diurnal) in serum phosphorus and urine phosphorus excretion, but in dialysis patients, this variability appears to be lost. No data exists for patients with stage 3 and 4 (pre-dialysis) CKD. Intestinal phosphorus absorption is also dependent on bioavailability (amount of free phosphorus available to be absorbed), which differs depending on the protein source, as the phosphorus in grain/soy diets is less bioavailable than that from protein from animal/casein protein source. In our animal model of CKD, these differences in bioavailability impact urinary phosphorus excretion and serum levels of
Sponsor: Indiana University

Current Primary Outcome: To determine if the dietary protein source affects fasting serum and urinary phosphorus excretion in patients with CKD stages 3 and 4. [ Time Frame: 6 months after baseline ]

Original Primary Outcome: Same as current

Current Secondary Outcome:

  • To determine if the protein source affects post prandial changes in serum and urinary phosphorus in patients with CKD stages 3 and 4. [ Time Frame: 6 months from baseline ]
  • To determine if changes in plasma FGF23 and PTH correlate with urinary phosphorus excretion in response to different protein sources in patients with CKD stages 3 and 4. [ Time Frame: 6 months from baseline ]


Original Secondary Outcome: Same as current

Information By: Indiana University

Dates:
Date Received: October 1, 2008
Date Started: October 2008
Date Completion:
Last Updated: June 22, 2011
Last Verified: June 2011