Abstract

Context: Bariatric surgery can be considered metabolic surgery, with important weight loss-independent effects on metabolism. Altered secretion of the intestinal hormone Glucagon-Like Peptide-1 (GLP-1) may be an important factor in the metabolic success of bariatric surgery. GLP-1 is an important regulator of glucose metabolism, reducing glycemia by regulating insulin and glucagon secretion, slowing gastric emptying, and lowering the desire for food intake. A potentiating effect of bariatric surgery on postprandial GLP-1 secretion is well documented and contributes to the increased insulin secretion and sensitivity that precedes weight loss. However, studies on patients with Normal Glucose Tolerance (NGT) are relatively few, and a clear consensus is still lacking in terms of potential effects of bariatric surgery on fasting GLP-1 levels in obese subjects with NGT.

Objective: To investigate fasting and postprandial levels of GLP-1 in obese women with NGT before and after bariatric surgery.

Design: Plasma GLP-1 was quantified at fasting and during an Oral Meal Tolerance Test (OMTT) in female patients with NGT subjected to Vertical Sleeve Gastrectomy (VSG) or Roux-en-Y Gastric Bypass (RYGB), preoperatively and 3 months postoperatively. Insulin resistance was quantified using HOMA-IR, and beta cell function using the Oral Disposition Index (DIo).

Setting: This study was performed at Karolinska Institutet, Södertälje Hospital south of Stockholm, Sweden.

Patients and participants: Eleven female patients aged 18-65 years with a BMI≥40 kg/m² and NGT were included. Exclusion criteria were T2D (based on the criteria of the American Diabetes Association (ADA) (2014)), prior GLP-1 based therapy or insulin therapy, and history of substance abuse (drugs or alcohol).

Main outcome measures: Outcome measures were fasting and OMTT plasma levels of insulin and GLP-1.

Results: Fasting GLP-1 levels were decreased 3 months postoperatively compared to baseline (12.3±1.5 vs. 20.1±3.4 pmol/L, p=0.05). Meal-stimulated GLP-1 secretion was significantly increased 3 months postoperatively in association with increased insulin sensitivity and enhanced beta cell function.

Conclusion: Bariatric surgery reduces fasting plasma GLP-1 levels, while significantly increasing meal-stimulated plasma GLP-1 levels, in obese women with NGT.

Keywords:Bariatric surgery; Normal Glucose Tolerance (NGT); Obesity; BMI; Glucagon Like Peptide 1 (GLP-1)

Abbreviations: GLP-1: Glucagon-Like Peptide-1; NGT: Normal Glucose Tolerance; OMTT: Oral Meal Tolerance Test; VSG: Vertical Sleeve Gastrectomy; RYGB: Roux-en-Y Gastric Bypass; T2D: Type 2 Diabetes; IGT: Impaired Glucose Tolerance; ADA: American Diabetes Association