Weight loss may curb kidney stone risk in obese patients

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * First time or recurrent calcium oxalate stone formers defined as composition of most recent stone \>50% calcium oxalate without uric acid component * Last stone passage or removal greater than 3 months prior to screening * Body Mass Index (BMI) \>35 kg/m2 * Able to provide consent * Hemoglobin A1C \<6.5% * Normal fasting blood CMP: Normal serum Na, K, Cl, CO2, Calcium, Albumin, AST, ALT \<2 times upper limit of normal, Glucose \<126 mg/dl, eGFR \>60 ml/min/1.73 m2. * 24-hour urine collection with creatinine within 20% of gender appropriate (mg creat/kg body weight) and consistent between collections (within 20% of each other) * Willing to ingest menus prepared at the University of Alabama and University of Texas Southwestern Clinical Research Units * Willing to consume the Optifast VLCD diet * Willing to ingest menus prepared in Metabolic kitchen. No food allergies or intolerance to any of the foods in study menus. Substitutions for lactose intolerance will be made. * Willing to avoid vigorous exercise during eucaloric, low-oxalate dietary phase * Willing to stop use of weight-loss medications * Willing to stop for 14 days before and during study: medications for stone prevention including diuretics, potassium citrate, allopurinol, febuxostat, and calcium, nutritional, or herbal supplements * Those with controlled hypertension (systolic blood pressure \<160 mmHg, diastolic \<90 mmHg) will be included. * Those without severe dyslipidemia (LDL \<200 mg/dL, HDL \>30 mg/dL, and triglycerides \<250 mg/dL) will be included. Treated and controlled dyslipidemia is accepted * Smoking/chewing tobacco/vaping will be allowed Exclusion Criteria: * Renal colic or past stone surgery in the past 3 months * Estimated Glomerular Filtration Rate (eGFR) less than 60 ml/min/1.73m2 * History of type 2 diabetes or screening hgb A1c greater than or equal to 6.5% * Alcohol or drug abuse. Alcohol consumption \>12 units per week and/or unwillingness to abstain from alcohol consumption 2 days before and during the study. * Mental/medical condition likely to impede study completion * Current/planned pregnancy or breastfeeding in coming 6 months, unwillingness to use effective method of birth control during the study for individuals of childbearing potential. * Planned vacation in coming 4 months * Febrile illness including flu/common cold/COVID-19 within 21 days of study start * Primary or enteric hyperoxaluria * Gastrointestinal disorder or surgery that impacts oxalate transport * Cirrhosis, pancreatic or biliary disorder, porphyria, gout * Malignancy treated within the past 12 months * Nephrotic syndrome, neurogenic bladder, urinary diversion * History of primary hyperparathyroidism, cystinuria, renal tubular acidosis, sarcoidosis, cystic fibrosis * Uncontrolled hypertension, myocardial infarction in past 6 months, unstable angina, congestive heart failure * Medications: Topiramate, acetazolamide, zonisamide, diuretics, SGLT2-inhibitors, immunosuppressants