The role of the proximal small intestine in improvements in diabetes resolution and insulin sensitivity following bariatric surgery in type 2 diabetes

Abstract

Bariatric surgery is an effective, rapid, and durable treatment for obesity and type 2 diabetes mellitus (T2DM). Roux-en Y Gastric Bypass (RYGB) resolves T2DM in 80% of cases, while gastric banding (LAGB) resolves T2DM in only 45%. One significant difference between RYGB and LAGB is the bypassing of the proximal small intestine in RYGB. Inadequate insulin secretion and insulin resistance are well known contributors to T2DM and both improve following RYGB. To determine if RYGB produces greater improvements in insulin secretion and insulin sensitivity than LAGB in T2DM, we studied obese, T2DM, Caucasian women who underwent RYGB (N=9) or LAGB (N=3). Insulin secretion (AIRg) and insulin sensitivity (Si) were measured pre- and 1-wk post-surgery by Minimal Model analysis following an insulin modified intravenous glucose tolerance test (IVGTT). Post-surgery analysis at 1-wk eliminates the potential contribution of differences in weight loss or food consumption as these are rigorously controlled for 1 wk following these surgical procedures. There was a trend (p = 0.053) for an increase in Si from pre-surgery to 1-wk post-surgery, but there was no difference in Si between surgical groups (RYGB, Pre: 0.85 ± 0.15 and 1-wk: 2.30 ± 0.43) and (LAGB, Pre: 1.32 ± 0.26 and 1-wk: 1.67± 0.60). There was a trend for an Interaction (p = 0.056) in AIRg with an increase in RYGB (Pre: 42.0 ± 23.3 and 1-wk: 94.7 ± 52.6), but decrease among LAGB (Pre: 519.7 ± 392.9 and 1-wk: 391.8 ± 291.6) with surgery. There was also a trend (p = 0.067) for a greater AIRg in LAGB compared to RYGB regardless of surgery status. These results in obese, T2DM, Caucasian women suggest that insulin sensitivity may be increased similarly in RYGB and LAGB questioning the role of the proximal small intestine bypass in the reversal of insulin sensitivity following bariatric surgery. In contrast, improvements in insulin secretion may be greater in RYGB than LAGB. Additional gastric banding patients are required to provide adequate power for statistical analysis.