Obesity has reached epidemic proportions in the USA and Europe, and is increasing world-wide. Morbid obesity (BMI>40kg/m2) is usually resistant to medical and dietary therapy while surgical treatment results in a permanent loss of most of the excess weight. The most popular technique today is the Roux-en-Y gastric bypass procedure which results in a weight loss of approximately 95 lbs per year or a 2/3 loss of the excess weight in 2 years (7-9). Weight loss occurs for 2 reasons: first the volume of the stomach is reduced, and second, the duodenum and first part of the jejunum is bypassed resulting in malabsorption. Although most patients tolerate the procedure well with a leveling off of weight loss close to the ideal body weight, a subpopulation of patients continue to lose weight, becoming progressively more malnourished, necessitating reversal of the surgery. To date, no studies have investigated what happens to pancreatic function in obese patients following bypass surgery, but from an understanding of the physiology of pancreatic stimulation, it is likely that the pancreas atrophies because the intestinal phase of pancreatic stimulation is bypassed and the inhibitory ileal brake is perpetually stimulated. In the following study we plan to investigate whether patients with excessive weight loss after bypass surgery develop malabsorption not only due to bypass of the upper GI tract but also because of impaired pancreatic enzyme secretion resulting from chronic activation of the ileal brake mechanism. Up to 20 post-bariatric surgery (Roux-en-Y) patients with excessive and continued weight loss will be screened for fat absorption and loss of pancreatic secretion. Those with loss of >20% fat absorption will then be treated at home with pancreatic enzyme supplements for a 3 month period to assess weight stabilization or gain. After 3 months, fat absorption and the pancreatic stimulation test will be repeated while patients are on enzyme supplementation to determine whether fat digestion and absorption has improved from baseline.