The obesity-related co morbidity most dramatically ameliorated by Roux-en-Y Gastric Bypass is type 2 diabetes mellitus (DM). ). In five published studies examining a total of 3568 people undergoing RYGB, diabetic patients enjoyed complete remission of their disease at rates ranging from 82 - 98%, with most studies showing resolution in approximately 83% of cases. The reversal of impaired glucose tolerance without DM was nearly universal. Patients whose DM remitted were able to discontinue all diabetic medications and manifest normal fasting glucose and glycosylated hemoglobin levels. Roux-en-Y Gastric Bypass is a highly effective method to reverse Diabetes Mellitus, which is traditionally regarded as a progressive, unrelenting disease. The beneficial effects of RYGB on DM, however, cannot be accounted for by weight loss alone. Perhaps the most impressive observation is that previously diabetic patients typically discontinue all of their DM medications at the time of discharge from the hospital after RYGB (~1 wk), long before major weight loss has occurred.
Eventually, amelioration of DM can be accounted for by the well-known effect of weight loss to increase insulin sensitivity. A more interesting possibility, which may act in concert with the above mechanism, is that favorable alterations in gut hormone release after RYGB improve insulin secretion and/or action.
Gastric Bypass for Obesity: Mechanisms of weight loss and Diabetes resolution. David E. Cummings et al. Journal of clinical endocrinology and metabolism, June 2004