To evaluate early changes in glycemia, insulin physiology and gut hormone responses to an easily tolerated and slowly ingested solid, low-carbohydrate mixed meal test (MMT) following laparoscopic adjustable gastric banding (LAGB) or Roux-en-Y gastric bypass (RYGB) surgery.SUBJECTS/METHODS:
This was a prospective non-randomized study. Plasma glucose, insulin and c-peptide (to estimate hepatic insulin extraction; %HIE), incretins (GIP, aGLP-1) and pancreatic polypeptide (PP) responses to the MMT were measured at 4–8 weeks before and after surgery in obese, metabolically healthy patients (RYGB = 10F or LAGB = 7F/1M). Supplementary clamp data on basal endogenous glucose production (EGP) and peripheral insulin action (Rd = rate of glucose disposal) and metabolic clearance rates of insulin (MCR-INS) were available in five of the RYGB patients. Repeated measures were appropriately accounted for in the analyses.RESULTS:
Following LAGB surgery, C-peptide and insulin MMT profiles (P = 0.004 and P = 0.0005, respectively) were lower with no change in %HIE (P = 0.98). In contrast, in RYGB subjects, both fasting glucose and insulin (Δ = - 0.66 mmol l-1, P ≤ 0.05 and Δ = - 44.4 pmol l-1, P < 0.05, respectively) decreased, and MMT glucose (P < 0.0001) and insulin (P = 0.001) but not c-peptide (P = 0.69) decreased. Estimated %HIE increased at fasting (Δ = 8.4%, P ≤ 0.05) and during MMT (P = 0.0005). Early (0–20 min) prandial glucose (0.27 ± 0.26 versus 0.006 ± 0.21 mmol l-1, P ≤ 0.05) and insulin (63(48, 66) versus 18(12, 24) pmol l-1, P ≤ 0.05) responses increased after RYGB. RYGB altered the trajectory of prandial aGLP-1 responses (treatment × trajectory P = 0.02), and PP was lower (P < 0.0001). Clamp data in a subset of RYGB patients showed early improvement in basal EGP (P = 0.001), and MCR-INS (P = 0.015).CONCLUSION:
RYGB results in distinctly different changes in plasma glucose, insulin and gut hormone response patterns to a solid, slowly ingested low-carbohydrate MMT versus LAGB. Altered nutrient delivery, along with indirect evidence for changes in hepatic and peripheral insulin physiology, are consistent with the greater early improvement in glycemia observed after RYGB versus LAGB surgery.