GI Oxalate Absorption Study for Kidney Stone Prevention

This study is investigating how the body absorbs oxalate, a substance in food, which can contribute to kidney stone formation. It involves a special low-oxalate diet for five days, followed by a full-day visit to the University of Chicago research clinic. Researchers will measure changes in oxalate levels in your urine to understand how the diet affects absorption. You might be eligible if you are 18-70 years old and have a history of calcium-based kidney stones, especially if you've had Roux-en-Y gastric bypass surgery or have a BMI of 30 or higher. The study aims to enroll 30 participants.

Study design
This is an interventional study planning to enroll 30 participants, divided into three groups: post-Roux-en-Y gastric bypass stone formers, obese stone formers, and non-obese stone formers.
What's involved
You would follow a special diet at home for two days, then eat special meals delivered from the clinic for three days. You will also collect urine samples at home and spend most of one day at the University of Chicago research clinic.
Compensation
Not stated in the trial record.
Follow-up
Your urine oxalate levels will be measured at 6 days after starting the low oxalate diet, and oxalate absorption will be measured at various time points up to 24 hours on day 6.

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NCT05356000

GI Oxalate Absorption

Recruiting
NAAges 18–70InterventionalPrevention
University of Chicago
~30 participants
Updated 2025-08-19 on ClinicalTrials.gov
What's tested:Special low-oxalate diet followed by all-day visit to University of Chicago research clinic

At a glance

Recruiting sites
1 of 1 listed site is recruiting right now
RecruitingSuspended, closed, or not yet open
What they're measuring
Change in 24-hour urine oxalate from baseline to after 5 days on low oxalate diet (2 days on participant managed, 3 days on clinical research center prepared diet of 50mg/day)
Measured over 6 days
+5 more outcomes measured
Bariatric Surgery Candidate
Kidney Stone
1 sites across 1 states
Illinois1

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Eligibility criteria

Inclusion

Age 18-70
Previous history of Roux-en-Y gastric bypass
History of at least one calcium-based kidney stone after surgery
Pre-protocol urine oxalate above the lab normal range (50mg/day)
Age 18-70
Body mass index (BMI) \>=30kg/m2
History of at least one calcium-based kidney stone
Pre-protocol urine oxalate above the lab normal range (50mg/day)
Age 18-70, BMI between 18.5-29.9 kg/m2
History of at least one calcium-based kidney stone

Exclusion

History of colon resection (partial or complete)
History of duodenal switch bowel surgery
History of ileal-jejunal bypass surgery
History of primarily uric acid, cysteine, or struvite stones
History of bowel surgery
History of colon resection
History of inflammatory bowel disease (Crohn's disease, Ulcerative Colitis)
History of primarily uric acid, cysteine, or struvite stones
  • Change in 24-hour urine oxalate from baseline to after 5 days on low oxalate diet (2 days on participant managed, 3 days on clinical research center prepared diet of 50mg/day)6 days

    24-hour urine oxalate will be measured before and after participants follow a low oxalate diet for 5 total days (3 days will be clinical research center prepared food with known measured oxalate content of 50mg/day)

  • Percent absorption of 13C2-oxalate from pre-load baseline (time 0) to 2, 4-, 6-, and 24-hour time points6 days

    Will be measured or calculated at time points 0, 2-hours, 4-hours, 6-hours and 24-hours after sodium 13C2-oxalate and sucralose consumption. We will compare change in urine total urine oxalate and 13C2-oxalate/total oxalate and sucralose each time period for all participants.

  • Change in urine 13C2-oxalate from pre-load baseline (time 0) to 2, 4-, 6-, and 24-hour time points6 days

    Will be measured or calculated at time points 0, 2-hours, 4-hours, 6-hours and 24-hours after sodium 13C2-oxalate and sucralose consumption. We will compare change in urine total urine oxalate and 13C2-oxalate/total oxalate and sucralose each time period for all participants.

  • Percent absorption total urine oxalate from pre-load baseline (time 0) to 2, 4-, 6-, and 24-hour time points6 days

    Will be measured or calculated at time points 0, 2-hours, 4-hours, 6-hours and 24-hours after sodium 13C2-oxalate and sucralose consumption. We will compare change in urine total urine oxalate and 13C2-oxalate/total oxalate and sucralose each time period for all participants.

  • Percent absorption of sucralose from pre-load baseline (time 0) to 2, 4-, 6-, and 24-hour time points6 days

    Will be measured or calculated at time points 0, 2-hours, 4-hours, 6-hours and 24-hours after sodium 13C2-oxalate and sucralose consumption. We will compare change in urine total urine oxalate and 13C2-oxalate/total oxalate and sucralose each time period for all participants.

  • Change in urine sucralose from pre-load baseline (time 0) to 2, 4-, 6-, and 24-hour time points6 days

    Will be measured or calculated at time points 0, 2-hours, 4-hours, 6-hours and 24-hours after sodium 13C2-oxalate and sucralose consumption. We will compare change in urine total urine oxalate and 13C2-oxalate/total oxalate and sucralose each time period for all participants.