Impact of Gastric Banding Versus Metformin on β-Cell Function in Adults With Impaired Glucose Tolerance or Mild Type 2 Diabetes

OBJECTIVE Type 2 diabetes (T2D) results from progressive loss of β-cell function. The BetaFat study compared gastric banding and metformin for their impact on β-cell function in adults with moderate obesity and impaired glucose tolerance (IGT) or recently diagnosed, mild T2D. RESEARCH DESIGN AND METHODS Eighty-eight people aged 21–65 years, BMI 30–40 kg/m2, with IGT or diabetes known for <1 year, were randomized to gastric banding or metformin for 2 years. Hyperglycemic clamps (11.1 mmol/L) followed by arginine injection at maximally potentiating glycemia (>25 mmol/L) were performed at baseline, 12 months, and 24 months to measure steady-state C-peptide (SSCP) and acute C-peptide response to arginine at maximum glycemic potentiation (ACPRmax) and insulin sensitivity (M/I). RESULTS At 24 months, the band group lost 10.7 kg; the metformin group lost 1.7 kg (P < 0.01). Insulin sensitivity increased 45% in the band group and 25% in the metformin group (P = 0.30 between groups). SSCP adjusted for insulin sensitivity fell slightly but not significantly in each group (P = 0.34 between groups). ACPRmax adjusted for insulin sensitivity fell significantly in the metformin group (P = 0.002) but not in the band group (P = 0.25 between groups). HbA1c fell at 12 and 24 months in the band group (P < 0.004) but only at 12 months (P < 0.01) in the metformin group (P > 0.14 between groups). Normoglycemia was present in 22% and 15% of band and metformin groups, respectively, at 24 months (P = 0.66 between groups). CONCLUSIONS Gastric banding and metformin had similar effects to preserve β-cell function and stabilize or improve glycemia over a 2-year period in moderately obese adults with IGT or recently diagnosed, mild T2D.