Roux-en-Y gastric bypass surgery, which is one of the most common bariatric procedure performed, involves surgeons creating a smaller stomach pouch that restricts food intake and bypasses large sections of the digestive system.
The researchers say in ideal circumstances it has a low rate of complication and results in sustained and meaningful weight loss, significant improvement in quality of life, improvement or resolution of obesity-associated comorbidities and extended life span.
However the team from the University of California, San Francisco, say up to 15% of patients do not lose weight successfully, despite perceived precise surgical technique and regular follow-up.
Dr. Guilherme M. Campos and his colleagues examined data from 361 patients who underwent gastric bypass at one institution between 2003 and 2006.
Poor weight loss was defined as losing 40% or less of excess body weight after 12 months and good weight loss as losing more than 40% of excess weight.
The examination of the yearly follow-up data on 310 of the patients, who had an average body mass index (BMI) of 52 before surgery showed they had an average BMI of 34 and had lost an average of 60 percent of their excess body weight.
However 38 patients (12.3%) had poor weight loss and after adjusting for other related factors, diabetes and having a larger size stomach pouch after gastric bypass surgery were independently associated with poor weight loss.
The researchers suggest that with diabetics on insulin or other drugs, the production of fat and cholesterol is stimulated and other factors too may lead to weight gain including a 'protective' increase in caloric intake to treat episodes of hypoglycemia (low blood sugar), reduction of urinary glucose losses and sodium and water retention that are a direct effect of insulin on the distal tubule in the kidney.
The researchers say the restriction on dietary intake imposed by a small stomach pouch is one of the most important aspects of gastric bypass surgery.
Research suggest that many surgeons estimate pouch size using anatomical landmarks rather than using a sizing balloon and the team say it is critical to stress the importance of and to teach the creation of the small gastric pouch and to better standardise the technique used for pouch creation.
They believe that a gastric bypass provides good or excellent weight loss for most patients, but for diabetics a larger pouch size are independently associated with poor weight loss after gastric bypass.
They say changes in the use of diabetes medications may reduce the risk of poor weight loss among diabetics undergoing gastric bypass but they suggest that detailed attention to the creation of a small gastric pouch is essential for achieving the best results.
This study was supported in part by a grant from the National Center for Research Resources and is published in the September issue of Archives of Surgery, one of the JAMA/Archives journals.