Stage 1 Key Inclusion Criteria:  Ages 18 to 55 Body mass index (BMI) < 38 kg/m2. Healthy as defined by no clinically relevant abnormalities being identified by a detailed medical history, physical examination, and clinical laboratory tests. If woman of child-bearing potential, must not be pregnant, and must also agree to use an appropriate highly-effective contraceptive. Willing and able to comply with all study requirements, including duration of stay at inpatient unit, dietary restrictions, daily study product administration, pregnancy testing and contraception (if applicable), stool collections, and blood and urine collections.  Stage 1 Key Exclusion Criteria:  Estimated glomerular filtration rate (eGFR) < 80 mL/min/1.73 m2 at Screening. Oral or parenteral antibiotics within 4 weeks prior to Screening, or anticipation of the need for such antibiotics during the Screening or treatment periods of the study. Current or history of any clinically significant medical illness or disorder the Investigator considers should exclude the subject from the study. Participation in any investigational intervention study within 30 days prior to study product administration in this study. Known hypersensitivity to omeprazole. Applicable only to certain study groups depending on emerging Stage 1 data: no current or anticipated use during the screening or treatment periods of the study of medications that have the potential for drug-drug interactions (DDI) with omeprazole.  Stage 2 Key Inclusion Criteria:  Ages 18 to 65. Hyperoxaluria secondary to Roux-en-Y gastric bypass surgery. 24-Hour urinary oxalate (UOx) ≥ 60 mg. If woman of child-bearing potential, must not be pregnant and must also agree to use an appropriate highly effective contraceptive method. Must, in the opinion of the Investigator, be in otherwise good health. Willing and able to comply with all study requirements, including dietary restrictions, daily study product administration, pregnancy testing and contraception (if applicable), stool collections, and blood and 24-hour urine collections.  Stage 2 Key Exclusion Criteria:  Chronic kidney disease with eGFR < 30 mL/min/1.73 m2 at Screening. Evidence of current acute renal injury or ongoing clinically significant renal disease. Oral or parenteral antibiotics within 4 weeks prior to Screening, or anticipation of the need for such antibiotics during the Screening or treatment periods of the study (topical antibiotics are permissible.) Taking during the study any treatment for hyperoxaluria except for NOV-001, other than stable treatments for the management of kidney stones. Taking Vitamin C ≥ 300 mg/day for > 10 days within 7 days prior to Screening; unwilling or unable to discontinue and/or avoid Vitamin C supplementation for the duration of study product treatment. Known active autoimmune disorder or other condition requiring high dose of systemic corticosteroids (i.e., > 10 mg/day prednisone or equivalent) or other immunosuppressant therapy. Current or history of any clinically significant medical illness or disorder other than enteric hyperoxaluria that the Investigator considers should exclude the patient from the study. Participation in any investigational intervention study within 30 days prior to study product administration in this study. Known hypersensitivity to omeprazole.