Study links gastric bypass surgery to increased risk of kid...(and improving diabetes Dr. Monga added....),Health

Surgeons conducted a prospective, longitudinal study of 24 morbidly obese adults (9 men and 15 women) from a university-based bariatric surgery clinic scheduled to undergo RYGB between December 2005 and April 2007. Five patients had a history of nephrolithiasis. Patients provided 24-hour urine collections for analysis seven days before and 90 days after operation. The primary endpoints were change in the amount of the compound oxalate in the urine and the relative supersaturation of calcium oxalate (that is, whether the urine contained more calcium oxalate than could normally be dissolved, potentially leading to crystallization) from baseline to three months post-RYGB. Both of these factors have been demonstrated by earlier studies to be major risk factors for the development of kidney stones.

Significant increases were noted in urinary oxalate excretion (31 10 mg/d versus 41 18 mg/d; p=0.026) and relative supersaturation of calcium oxalate (1.73 0.81 versus 3.47 2.59; p=0.030) at only three months post-RYGB. Six patients (25%) developed de novo hyperoxaluria, with oxalate excretion increasing from 26 12 mg/d to 63 12 mg/d (p =0.0046) There were no preoperative patient characteristics predictive of increased risk of kidney stone formation.

The reason for increased likelihood of the development of kidney stones following this type of gastric bypass surgery is not entirely understood. A possibility is that the anatomic rearrangement caused by the operation establishes a mildly malabsorptive state, which may be responsible for the increase in the excretion of urinary electrolytes. Kidney stones could also result from an alteration in the gut microflora (normal bacteria) caused by the procedure.

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