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