OBJECTIVE: To identify the effect of a controlled metabolic diet on reducing 
urinary calcium oxalate (CaOx) supersaturation in subjects with hyperoxaluric 
nephrolithiasis after potentially malabsorptive forms of bariatric surgery.
METHODS: Subjects with a history of CaOx kidney stones and mild hyperoxaluria 
after bariatric surgery (n = 9) collected baseline 24-hour urine samples while 
consuming a free choice diet. They were then instructed to consume a controlled 
diet low in oxalate (70-80 mg/d), normal in calcium (1000 mg/d), and moderate in 
protein before 2 final 24-hour urine collections.
RESULTS: Overall, the urinary CaOx supersaturation decreased from 1.97 ± 0.49 
delta Gibbs (DG) with the free choice diet to 1.13 ± 0.75 DG with the controlled 
diet (P < .01). This occurred in the absence of a significant change in urinary 
oxalate excretion (0.69 ± 0.29 mmol/d with the free choice diet compared with 
0.66 ± 0.38 mmol/d with the controlled diet). Urinary volume, citrate, and pH 
all increased, although not significantly (P > .05), contributing to the 
significant CaOx supersaturation change.
CONCLUSION: A controlled metabolic diet normal in calcium, moderate in protein, 
and reduced in oxalate can positively affect urinary CaOx supersaturation after 
bariatric surgery. However, this diet did not appear to decrease urinary oxalate 
excretion. Therefore, restriction of dietary oxalate alone might not be enough 
to reduce urinary oxalate excretion to normal levels in this group of patients 
with known enteric hyperoxaluria. Additional strategies could be necessary, such 
as the use of oral calcium supplements as oxalate binders and a lower fat diet.