Inclusion Criteria

• age 19-70 yrs
• Body Mass Index > 18.5 kg/m2
• First time or recurrent Calcium Oxalate stone former. Composition of most recent stone ≥ 50% calcium oxalate if available
• Not colonized with Oxalobacter formigenes
• Normal fasting serum electrolytes on comprehensive metabolic profile
• Willing to ingest fixed diets
• Willing to stop supplements (vitamins including vitamin C, calcium (citrate or carbonate) and other minerals, herbal supplements, nutritional aids, probiotics) for 2 weeks before start and during fixed diet phases.
• If on medications for stone prevention (e.g. thiazides, citrate, allopurinol), stable dose regimen for at least 2 weeks prior to and during study

Exclusion Criteria

• Chronic Kidney Disease stage 4-5
• Primary hyperoxaluria
• Liver, endocrine or renal diseases (other than idiopathic Calcium Oxalate kidney stones) or any other condition that may influence the absorption, transport or urinary excretion of ions, which will compromise the interpretation of results, including: Cystic fibrosis, Cystinuria, Uric acid stone former, Nephrotic syndrome, Sarcoidosis, Renal tubular acidosis, Primary hyperparathyroidism, Neurogenic bladder, Urinary diversion
• Pregnancy or breast-feeding
• Incompatible dietary requirements with the study, food allergies or intolerance to any of the foods in study menus
• Active malignancy or treatment for malignancy within 12 months prior to screening
• Utilization of immunosuppressive medication
• Uncontrolled Hypertension or diabetes
• Diabetes type 1
• Current Colonization with Oxalobacter formigenes