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Investigators at the University of California have identified diabetes and larger post-surgical pouch as independent predictors of poor weight loss one year after gastric bypass.

Investigators at the University of California, San Francisco, have identified diabetes and larger post-surgical pouch size as independent predictors of poor weight loss one year after gastric bypass.

Up to 15 per cent of patients who undergo gastric bypass surgery fail to lose enough weight to appreciably improve their health, Dr. Guilherme M. Campos and colleagues note in the September issue of the Archives of Surgery.

The team examined factors related to weight loss 12 months after gastric bypass surgery for 310 patients treated at their tertiary referral center between 2003 and 2006. Average age was 45 years, and mean preoperative BMI was 52.

According to the report, the overall mean excess weight loss at one year was 60 per cent, resulting in a mean BMI of 34.

Thirty-eight patients (12 per cent) had poor weight loss, defined as a decrease of 40 per cent or less of excess weight, and a final mean BMI of 44. Gastric pouch area, determined by swallow studies of the upper gastrointestinal tract obtained on postoperative day one, was 39 cm² in those with poor weight loss and 25 cm² in those with good weight loss.

In multivariate analysis, only the presence of diabetes (odds ratio 3.09, p = 0.007) and larger pouch size (OR 2.77, p < 0.001 per standard deviation) were independently associated with poor weight loss.

Initial BMI, sociodemographic variables, other obesity-related comorbidities, and surgical factors - including surgical approach, gastrojejunostomy technique, and alimentary limb length - were not associated with weight loss outcomes.

One explanation for the association between poor weight loss and diabetes, the authors suggest, is the use of insulin - an anabolic hormone - and/or drugs that increase circulating insulin levels, including sulfonylureas, meglitinides, and thiazolidinediones.

Medications not linked to weight gain, such as metformin, alpha-glucosidase inhibitors, exenatide, sitagliptin, and vildagliptin, "may be considered in patients who continue to need exogenous glucose control and thus may improve weight loss after gastric bypass."

Moreover, they conclude, "detailed attention to the creation of a small gastric pouch is essential for achieving the best results."

Arch Surg 2008;143:877-884