Objective:

To examine glucose metabolism and β-cell function in patients with type 2 diabetes mellitus (T2DM) after two types of bariatric intervention; Roux-en-Y gastric bypass (RYGB) and gastric restrictive (GR) surgery.

Design:

Prospective, nonrandomized, repeated-measures, 4-week, longitudinal clinical trial.

Patients:

In all, 16 T2DM patients (9 males and 7 females, 52±14 years, 47±9 kg m− 2, HbA1c 7.2±1.1%) undergoing either RYGB (N= 9) or GR (N= 7) surgery.

Outcome measures:

Glucose, insulin secretion, insulin sensitivity at baseline, and 1 and 4 weeks post-surgery, using hyperglycemic clamps and C-peptide modeling kinetics; glucose, insulin secretion and gut-peptide responses to mixed meal tolerance test (MMTT) at baseline and 4 weeks post-surgery.

Results:

At 1 week post-surgery, both groups experienced a similar weight loss and reduction in fasting glucose (P< 0.01). However, insulin sensitivity increased only after RYGB,(P< 0.05). At 4 weeks post-surgery, weight loss remained similar for both groups, but fasting glucose was normalized only after RYGB (95±3 mg 100 ml− 1). Insulin sensitivity improved after RYGB (P< 0.01) and did not change with GR, whereas the disposition index remained unchanged after RYGB and increased 30% after GR (P= 0.10). The MMTT elicited a robust increase in insulin secretion, glucagon-like peptide-1 (GLP-1) levels and β-cell sensitivity to glucose only after RYGB (P< 0.05).

Conclusion:

RYGB provides a more rapid improvement in glucose regulation compared with GR. This improvement is accompanied by enhanced insulin sensitivity and β-cell responsiveness to glucose, in part because of an incretin effect.