Urologic Diseases Research Updates
No Link between Kidney Stones and Gastric Banding
According to a study supported by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), gastric banding-a surgical procedure that reduces the size of the stomach-does not increase the risk of kidney stones.
Gastric banding is one of several bariatric surgeries used to treat obesity. These surgeries are becoming more common due to surgical innovations, greater availability, and rising obesity rates. An estimated 30 percent of American adults are obese with a body mass index (BMI) of 30 or higher. BMI is a measure of weight in relation to height. Although initially reserved for people with extreme obesity-those with a BMI of 40 or higher-bariatric surgery's effectiveness in helping people shed pounds, reverse cardiovascular disease risk factors, and, in some cases, eliminate type 2 diabetes has caused doctors to consider it as a therapy for people with milder obesity.
The two most common bariatric procedures, gastric banding and Roux-en-Y gastric bypass (RYGB), help patients achieve significant weight loss and are relatively safe in the short term, according to the NIDDK-funded Longitudinal Assessment of Bariatric Surgery study. In gastric banding, the surgeon places an adjustable band around the top portion of the stomach, thereby limiting food intake. RYGB limits food intake by reducing the size of the stomach and diverting food around the lower portion of the stomach and part of the small intestine, reducing the body's ability to absorb calories.
The long-term risks of bariatric surgery are still under investigation. Studies have shown that RYGB increases the risk of kidney stone formation as soon as 6 months after surgery. Other studies have found higher urinary oxalate levels among people who underwent RYGB or similar gastric bypass procedures, compared with controls that had no surgery. Along with limiting the absorption of food, RYGB also limits the absorption of fat, which is shuttled to the colon where it may facilitate the absorption of oxalate-a salt cleared by the kidneys and a major constituent of kidney stones. Michelle J. Semins, M.D., senior resident in urology at The Johns Hopkins University School of Medicine, and colleagues wanted to learn whether a similar risk was associated with gastric banding.
"As a consequence of the efficacy of bariatric surgery, the past decade has witnessed a 10-fold increase in these procedures," wrote Semins and colleagues in a report in the August 15, 2009, online issue of Urology. "Until our present analysis, though, the effect of gastric banding on kidney stone disease has never been described."
The researchers compared the prevalence of kidney stone disease between two similar groups of obese individuals: one had gastric banding surgery and the other received no bariatric surgery. The average age in both groups was 46 years and about 80 percent of participants were female. Excluded were individuals with prior kidney disease, including kidney stones.
Whereas previous studies of RYGB patients showed a higher prevalence of kidney stones compared with controls, the present study showed the opposite. Two years after gastric banding, 1.49 percent of participants in the surgery group had been diagnosed with kidney stones, compared with 5.97 percent of control group participants. One participant from each group underwent a urological procedure to treat the stones.
The researchers speculated the significantly lower prevalence of kidney stones in the gastric banding group may have been a result of weight loss, as obesity is an independent risk factor for kidney stone disease. A lower BMI would, presumably, decrease kidney stone risk.
"In one sense, the present study is a negative one, in that it failed to demonstrate an increase in the prevalence of stone disease after gastric banding," wrote Semins, et al. "However, in this clinical situation such negative data are particularly necessary." Armed with these data, health care providers are better suited to help patients-especially those with a history of kidney stone disease-weigh the risks and benefits of bariatric surgery.
Semins and colleagues urged larger and longer follow-up studies to verify their findings. Since the publication by Semins, et al., a retrospective, epidemiological study supporting their findings was published by Penniston and colleagues in the November 2009 issue of The Journal of Urology. Urology will soon publish a second article about gastric banding by Semins, et al.
The study was funded by the Hariri Family Foundation and Mr. and Mrs. Chad and Nissa Richinson.
The NIDDK has health information about the complications of obesity, kidney stones, and bariatric surgery. For more information, visit www.niddk.nih.gov.
NIH Publication No. 10-5743