The purpose of this study is to determine whether or not the length of the biliopancreatic limb of the Roux-en-Y anastamosis plays a critical role in the development of malabsorption after gastric bypass for treatment of severe obesity.

Successful surgical treatment of severe obesity by RYGB is believed to require a procedure that (a) restricts the consumption of combustible food energy, and (b) reduces the intestinal absorption of food energy that is consumed. However, with RYGB operations that are currently employed, many patients do not develop the malabsorption they presumably require to produce good long term control of their body weight. It is important to find a way to do RYGB surgery in a way that consistently produces a moderate degree of fat malabsorption.

Patients who are scheduled to receive a RYGB for treatment of severe obesity will be randomly assigned to receive 2 variations of the standard operation. The stomach and duodenal bypass, and the creation of a small gastric pouch will be exactly the same for all patients. There will be differences in the two jejunal limbs which create the Roux-en-Y anastomosis. In Procedure A, the Roux limb length will be 150 cm, and the biliopancreatic limb will contain 40 cm of jejunum. In Procedure B, the Roux limb length will be 110 cm and the biliopancreatic limb will contain 80 cm of jejunum. The total length of jejunum in both limbs is 190 cm in both procedures. Thus, the only difference between procedures A and B is that B procedure has a larger percentage of jejunum in the biliopancreatic limb (80/190=42%) than procedure A (40/190 = 21%). A total of 20 patients will be studied, 10 with each procedure. Before and after RYGB, the patients will be studied in a clinical research laboratory. Dietary intake and intestinal absorption of fat, protein, carbohydrate and combustible energy will be measured by metabolic balance techniques for 72 hours. We hypothesize that fat malabsorption after bypass will be greater and more consistent in patients who receive the longer biliopancreatic limb than in the patients who receive the longer Roux limb.

Inclusion Criteria:

• Patients with severe obesity (BMI equal to or greater than 50) who have been scheduled to receive Roux-en-Y gastric bypass.

Exclusion Criteria:

• Previous abdominal surgery, chronic diarrhea, and severe constipation.