I had Roux-en-Y gastric bypass surgery done about 15 months ago and have lost 100 pounds so far. I just switched to a new primary-care physician, an osteopath, who recommends reversal of this surgery once I attain my weight goal, due to complications two of his patients have had. He cites bacteria buildup in the unused portion of the stomach as a cause of side effects. Are there any studies to back him up? My side effects so far have been mild -- occasional diarrhea and loose stools.

N.A.

Surgical procedures for obesity have evolved over the years as more experience has been gained in this field of medicine. Early types of operations led to unacceptable rates of long-term complications, including liver failure and severe nutritional deficiencies. Today, the surgeries done to treat severe obesity fall into one of two general categories: stapling of the stomach or bypass of the stomach. Some newer modifications of these procedures even combine these two methods.

Current procedures, including your Roux-en-Y surgery, are very effective, and patients can expect to lose about 40-60 percent of the excess weight. However, the success rate can vary greatly depending on the surgeon. In weight-loss surgery, it is crucial to find a surgeon with experience in performing these procedures.

Complications of today's weight-loss surgeries can be categorized as early and late. Early complications, which occur soon after the operation, are usually due to poor operative technique. These include leakage or obstruction at the surgical site. Later complications are a consequence of changes in the digestive tract after the operation. These include certain vitamin deficiencies that are most often seen in bypass patients. The deficiencies occur because food bypasses the upper part of their small intestines -- a region essential to the absorption of many vitamins. Generally, such problems can be treated with vitamin supplements.

Diarrhea is also common after weight-loss surgery. It occurs because the coordinated mixing of food with digestive enzymes is altered. However, despite the diarrhea, patients usually absorb enough calories, and malnutrition is rare. Other rarer long-term complications include ulcers in the remaining stomach, obstruction of the stomach and a breakdown of the staple-line.

Most patients who undergo operations performed by surgeons with proper experience have good long-term results. To address your specific question, there is rarely a need to reverse the procedure, and this may be a difficult undertaking given the scarring from the initial procedure.