Fibroblast Growth Factor-23 (FGF23) Reduction in Predialysis Chronic Kidney Disease (CKD)

Inclusion Criteria: * We will include stage 3a, 3b and 4 CKD patients, aged 18 years or over with normal serum phosphate levels (≤ 4.6 mg/dl) Exclusion Criteria: * Patients with rapidly advancing renal failure who thus might develop hyperphosphatemia or end stage renal disease requiring initiation of dialysis during the study period * Patients expected to require dialysis initiation within the follow up period * Patients with hyperphosphatemia \> 4.6 mg/dl * Patients with any previous or current treatment with phosphate binders or active vitamin D (doxercalciferol or calcitriol) * Malnutrition, defined as a serum albumin \< 3.0 mg/dl * Patients with liver disease (ALT or AST \> 100 U/L) or cholestasis (direct bilirubin \> 1.0 mg/dl) because this can limit their ability to absorb fat soluble vitamins such as vitamin D * Anemia, defined as a hematocrit \< 27% at the screening visit * Medical conditions impacting Pi metabolism-primary hyper- or hypoparathyroidism; Patients with previous subtotal parathyroidectomy; gastrointestinal malabsorption disorders such as Crohn's Disease, ulcerative colitis, celiac disease, or severe liver dysfunction; * Patients with outpatient counseling by a renal nutritionist within the previous 6 months * Hospitalization within the previous 4 weeks * Pregnancy or breastfeeding mothers * Patients unable to independently provide written informed consent - prisoners, mentally incompetent, minors