Gastric Bypass Is Less Effective in Patients With Diabetes, Larger Pouch Size

Posted Sep 15, 2008.By Mary Ann Moon

Among patients undergoing gastric bypass, those with diabetes and those with larger pouch sizes are the least likely to achieve sustained and meaningful weight loss, according to a report in the September issue of the Archives of Surgery.

In contrast, several other patient and procedural factors, including baseline weight and surgical technique, were not found to be predictors of surgery success, said Dr. Guilherme M. Campos and his associates at the University of California, San Francisco.

An estimated 5%-15% of patients do not lose weight successfully after gastric bypass, despite precise surgical technique and regular follow-up. The investigators assessed the effects of 17 possible variables on weight loss 1 year after gastric bypass in a prospective study of 310 patients treated at their medical center.

The mean subject age was 45 years (range, 19-69 years), the mean preoperative weight was 141 kg, and mean body mass index was 52 kg/m². Approximately 65% of the subjects had hypertension, 37% had diabetes, and 32% had obstructive sleep apnea related to their obesity.

One year after bypass, 38 subjects (12%) showed poor weight loss, which was defined as a loss of 40% or less of excess weight. In a multivariate analysis, only the presence of diabetes and larger pouch size were independently associated with poor weight loss.

Patients with diabetes had three times the risk of poor weight loss as did nondiabetic patients, and the association was strongest for those taking insulin rather than oral hypoglycemic agents. "Because insulin is a known anabolic hormone that promotes lipogenesis, stimulation of triglyceride synthesis, adipocyte differentiation, and muscle synthesis, elevated levels may reduce the degree of weight loss after gastric bypass," the investigators said (Arch. Surg. 2008;143:877-84).

Similarly, a larger stomach pouch as estimated on upper GI imaging studies raised the risk of poor weight loss by a factor of 2.7. Subjects with "good" weight loss had a mean pouch area of 25 cm², while those with "poor" weight loss had a mean pouch area of 39 cm².

In contrast, factors such as age, race, sex, marital status, insurance status, baseline weight, and baseline BMI did not affect weight loss. Comorbidities such as hypertension, arthritis, degenerative joint disease, and obstructive sleep apnea also had no effect on outcomes. Likewise, surgical variables such as the type of approach, the gastrojejunostomy technique, and the length of the alimentary limb did not predict weight loss.

These findings "could be used to develop more specific guidelines for informing patients preoperatively about the likelihood of a suboptimal outcome and for guiding the decision to undertake bariatric surgery. They also could be used to develop better strategies to overcome modifiable risk factors," Dr. Campos and his associates said.

In particular, "We believe it is critical to stress the importance of and to teach the creation of the small gastric pouch and to better standardize the technique used for pouch creation," they noted.