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Gastric Bypass Surgery May Not Be Effective for Weight Loss

Posted: Wednesday, October 22, 2008

Gastric bypass (GBP) surgery is an effective way for most patients to lose weight, but poor results are associated with diabetes and larger gastric pouch size, according to the results of a prospective cohort study.

"[GBP] is the most common operation performed in the United States for morbid obesity," write Guilherme M. Campos, MD, from the University of California, San Francisco (UCSF), and colleagues. "However, weight loss is poor in 10% to 15% of patients. We sought to determine the independent factors associated with poor weight loss after GBP."

At a university tertiary referral center, all patients at UCSF who underwent GBP from January 1, 2003, through July 30, 2006, were evaluated for weight loss at 12 months, which was defined as poor (≤40% excess weight loss) or good (>40% excess weight loss). Demographic, operative, and follow-up data were also collected.

Multivariate analysis determined the association with weight loss of variables including age, sex, race, marital and insurance status, initial weight, body mass index (BMI), comorbidities, and operative factors. Comorbid conditions investigated included diabetes mellitus, hypertension, joint disease, sleep apnea, hyperlipidemia, and psychiatric disease. Operative variables included laparoscopic vs open surgery, gastric pouch area, gastrojejunostomy technique, and alimentary limb length.

At 12 months, follow-up data were available for 310 (85.9%) of the 361 patients who underwent GBP during the study period. Preoperative mean BMI was 52 kg/m2 (range, 36 – 108 kg/m2), mean BMI at follow-up was 34 kg/m2 (range, 17 – 74 kg/m2), and mean excess weight loss at follow-up was 60% (range, 8% – 117%). Weight loss was poor in 38 patients (12.3%).

Univariate analysis revealed 4 variables associated with poor weight loss (greater initial weight, diabetes, open approach, and larger pouch size). However, the only significant predictors remaining after multivariate analysis were diabetes (P = .007) and larger pouch size (P < .001).

"[GBP] results in substantial weight loss in most patients," the study authors write. "Diabetes and larger pouch size are independently associated with poor weight loss after GBP."

Limitations of this study include that it was set in a tertiary care medical center with distinctive demographics and clinical characteristics; an inability to determine whether postoperative use of medications for diabetes had an effect on weight loss because only preoperative medication use was ascertained; a lack of data regarding factors that may have affected weight loss, including physical activity level, measures of body composition, and fat distribution before or after surgery; the lower prevalence of 2 risk factors for poor weight loss among the 51 patients omitted from analysis for lack of 12 months of follow-up data; and possible unmeasured confounders.

"Changes in the use of diabetes medications may reduce the risk of poor weight loss among diabetics undergoing GBP," the study authors write. "Detailed attention to the creation of a small gastric pouch is essential for achieving the best results."
Practice Pearls:

* Overall, GBP was effective, with weight loss characterized as poor (≤40% excess weight loss) in only 12.3% of patients. Mean BMI at follow-up was 34 kg/m2 (range, 17 – 74 kg/m2), and mean excess weight loss at follow-up was 60% (range, 8% – 117%).
* Multivariate analysis revealed that the only significant predictors of poor weight loss were diabetes and larger pouch size. The investigators concluded that creating a small gastric pouch is essential for achieving the best results.