title: Fat malabsorption and increased intestinal oxalate absorption are common after Roux-en-Y gastric bypass surgery.
abstract: BACKGROUND
  Hyperoxaluria and increased calcium oxalate stone formation occur after Roux-en-Y gastric bypass (RYGB) surgery for morbid obesity. The etiology of this hyperoxaluria is unknown. We hypothesized that after bariatric surgery, intestinal hyperabsorption of oxalate contributes to increases in plasma oxalate and urinary calcium oxalate supersaturation.
  
  
  METHODS
  We prospectively examined oxalate metabolism in 11 morbidly obese subjects before and 6 and 12 months after RYGB (n = 9) and biliopancreatic diversion-duodenal switch (BPD-DS) (n = 2). We measured 24-hour urinary supersaturations for calcium oxalate, apatite, brushite, uric acid, and sodium urate; fasting plasma oxalate; 72-hour fecal fat; and increases in urine oxalate following an oral oxalate load.
  
  
  RESULTS
  Six and 12 months after RYGB, plasma oxalate and urine calcium oxalate supersaturation increased significantly compared with similar measurements obtained before surgery (all P ≤ .02). Fecal fat excretion at 6 and 12 months was increased (P = .026 and .055, 0 vs 6 and 12 months). An increase in urine oxalate excretion after an oral dose of oxalate was observed at 6 and 12 months (all P ≤ .02). Therefore, after bariatric surgery, increases in fecal fat excretion, urinary oxalate excretion after an oral oxalate load, plasma oxalate, and urinary calcium oxalate supersaturation values were observed.
  
  
  CONCLUSIONS
  Enteric hyperoxaluria is often present in patients after the operations of RYGB and BPD-DS that utilize an element of intestinal malabsorption as a mechanism for weight loss.
authors.affiliation: Nephrology and Hypertension Research Unit, Division of Nephrology, Mayo Clinic College of Medicine, Mayo Clinic, Rochester, MN 55905, USA. rkumar@mayo.edu
authors.forename: Rajiv
authors.initials: R
authors.lastname: Kumar
authors.forename: John C
authors.initials: JC
authors.lastname: Lieske
authors.forename: Maria L
authors.initials: ML
authors.lastname: Collazo-Clavell
authors.forename: Michael G
authors.initials: MG
authors.lastname: Sarr
authors.forename: Ellen R
authors.initials: ER
authors.lastname: Olson
authors.forename: Terri J
authors.initials: TJ
authors.lastname: Vrtiska
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Bergstralh
authors.forename: Xujian
authors.initials: X
authors.lastname: Li
mesh_terms: D000328:Adult; D000368:Aged; D002129:Calcium Oxalate / Q000652:urine; D004041:Dietary Fats / Q000378:metabolism*; D005260:Female; D005500:Follow-Up Studies; D015390:Gastric Bypass; D006801:Humans; D006959:Hyperoxaluria / Q000209:etiology / Q000378:metabolism*; D007408:Intestinal Absorption / Q000502:physiology*; D008286:Malabsorption Syndromes / Q000209:etiology / Q000378:metabolism*; D008875:Middle Aged; D053040:Nephrolithiasis / Q000453:epidemiology / Q000652:urine; D009767:Obesity, Morbid / Q000601:surgery*; D010070:Oxalates / Q000378:metabolism*; D011183:Postoperative Complications; D011446:Prospective Studies; D012307:Risk Factors; D015431:Weight Loss / Q000502:physiology
chemical_list: D004041:Dietary Fats; D010070:Oxalates; D002129:Calcium Oxalate