title: Response to dietary oxalate after bariatric surgery.
abstract: OBJECTIVE
  Bariatric surgery (BS) may be associated with increased oxalate excretion and a higher risk of nephrolithiasis. This study aimed to investigate urinary abnormalities and responses to an acute oxalate load as an indirect assessment of the intestinal absorption of oxalate in this population.
  
  
  METHODS
  Twenty-four-hour urine specimens were collected from 61 patients a median of 48 months after BS (post-BS) as well as from 30 morbidly obese (MO) participants; dietary information was obtained through 24-hour food recalls. An oral oxalate load test (OLT), consisting of 2-hour urine samples after overnight fasting and 2, 4, and 6 hours after consuming 375 mg of oxalate (spinach juice), was performed on 21 MO and 22 post-BS patients 12 months after BS. Ten post-BS patients also underwent OLT before surgery (pre-BS).
  
  
  RESULTS
  There was a higher percentage of low urinary volume (<1.5 L/d) in post-BS versus MO (P<0.001). Hypocitraturia and hyperoxaluria (P=0.13 and P=0.36, respectively) were more frequent in BS versus MO patients. The OLT showed intragroup (P<0.001 for all periods versus baseline) and intergroup differences (P<0.001 for post-BS versus MO; P=0.03 for post-BS versus pre-BS). The total mean increment in oxaluria after 6 hours of load, expressed as area under the curve, was higher in both post-BS versus MO and in post-BS versus pre-BS participants (P<0.001 for both).
  
  
  CONCLUSIONS
  The mean oxaluric response to an oxalate load is markedly elevated in post-bariatric surgery patients, suggesting that increased intestinal absorption of dietary oxalate is a predisposing mechanism for enteric hyperoxaluria.
authors.affiliation: Nephrology Division, Federal University of São Paulo, São Paulo, Brazil.
authors.forename: Leila
authors.initials: L
authors.lastname: Froeder
authors.forename: Carlos Haruo
authors.initials: CH
authors.lastname: Arasaki
authors.forename: Carlos Alberto
authors.initials: CA
authors.lastname: Malheiros
authors.forename: Alessandra Calábria
authors.initials: AC
authors.lastname: Baxmann
authors.forename: Ita Pfeferman
authors.initials: IP
authors.lastname: Heilberg
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D050110:Bariatric Surgery / Q000009:adverse effects*; D002118:Calcium / Q000652:urine; D016009:Chi-Square Distribution; D002951:Citrates / Q000652:urine; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D006959:Hyperoxaluria / Q000209:etiology / Q000652:urine*; D007408:Intestinal Absorption; D008274:Magnesium / Q000652:urine; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000652:urine*; D010070:Oxalates / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000652:urine*; D020624:Oxalobacter formigenes; D018709:Statistics, Nonparametric; D014508:Urea / Q000652:urine; D014527:Uric Acid / Q000652:urine; D014556:Urine / Q000382:microbiology
chemical_list: D002951:Citrates; D010070:Oxalates; D014527:Uric Acid; D014508:Urea; D003404:Creatinine; D008274:Magnesium; D002118:Calcium