A Pilot Study of Oxalate Absorption in Secondary Hyperoxaluria

Inclusion Criteria: * Males or non-pregnant and non-lactating females * History of hyperoxaluria secondary to a known underlying enteric disease (e.g., Crohn's disease, bariatric surgery, and others) or without a known underlying cause (idiopathic), and kidney stones. * Urinary oxalate ≥ 40 mg of oxalate/24 hr at screening. * If taking drugs for the prevention of stone disease, including pyridoxine, thiazides (chlorthalidone, hydrochlorothiazide, and indapamide), citrate supplements, and allopurinol, there must have been no changes in these medications for at least one month prior to screening and no changes are anticipated for the duration of the study. * Able to understand and provide written informed consent. Exclusion Criteria: * Under or over-collection on screening 24-hour urine collection (mg creatinine/kg body weight outside of gender-specific range). * Estimated glomerular filtration rate (eGFR) \<40 mL/minute/1.73 m\^2 or acute renal failure. * Primary hyperoxaluria. * Allergy, intolerance, or any other factors limiting ability to consume the study foods or adhere to the study meal schedule. * Positive pregnancy test during Screening. * Clinically significant findings (including acute renal colic), an ongoing clinically significant illness requiring changes in management, or any planned medical/surgical procedure during the study. * Malignancy undergoing active therapy; patients in remission on chronic suppressive or maintenance therapies are not excluded. * Investigational compound within 30 days prior to screening. * Investigator determined that the subject would not be able to adhere or to complete the study procedures , or could not discontinue Vitamin C supplements, calcium supplements, or other medications that could interfere with oxalate absorption and/or excretion.