Phosphate Assessment in Chronic Kidney Disease Patients Study

Inclusion Criteria: * Men or women aged 18 years or older, of any race/ethnicity * Women must either be post-menopausal or have no monthly menstrual cycle * Estimated total daily energy expenditure (TDEE) of 1700 - 2700 calories * eGFR \>15 ml/min/1.73m2 - \< 60 ml/min/1.73m2 for the CKD group (CKD Stage 3 or Stage 4) * eGFR ≥ 60 ml/min/1.73m2 and negative urine protein on dipstick test for the non-CKD group * English speaking Exclusion Criteria: * Pregnant, currently breastfeeding, or \<3 months postpartum * Current dialysis or kidney transplant patient * Current use of insulin or chemotherapy drugs * Smokes cigarettes or uses e-cigarettes (vapes) * Uses nicotine products or other recreational drugs * Medical history of stroke or myocardial infarction (MI) * Medical history of conditions that can affect phosphate metabolism (i.e., uncontrolled thyroid disorder, parathyroid disorder, or gastrointestinal malabsorption disorders \[Crohn's, ulcerative colitis, and celiac disease\], cirrhosis) * Current use of certain medications that directly alter phosphate levels (i.e., phosphate binders; phosphate supplements, irregular use of iron) * Regular use of laxatives * Hypo- or hyperphosphatemia (serum phosphate \< 2.5 or \> 4.6 mg/dl) * Hypo- or hypercalcemia (serum calcium \< 8.4 or \> 10.7 mg/dl) * Severe anemia (hemoglobin \< 8 g/dl for women and \< 9 g/dl for men) * Severe hyperglycemia (serum blood glucose \> 300 mg/dl) * Body weight less than \<110 lbs (due to risk for phlebotomy-induced anemia) * Received a blood transfusion in the last four months * Extreme hypertension as demonstrated by a blood pressure \> 180/120 as the average of 3 blood pressures taken during the screening/baseline, or extremely low blood pressure \< 80/50 * Unwilling or unable to eat study meals * Lack of access to a functional refrigerator or freezer * Lack of access to a microwave or conventional oven * On low potassium diet * On low phosphate diet * Specific dietary restrictions (i.e. vegetarian, vegan, ketogenic, etc.) * Food allergies including but not limited to milk, egg, soy, nuts, shellfish, and wheat or gluten * Allergic to sodium phosphate * Unable or unwilling to complete urinary sample collection or food diaries * Unable or unwilling to provide informed consent * Unable to read or speak English * Participant in other conflict clinical trial * Unable to complete the study measurements * Unsafe to participate in this study per investigator's judgement