ABSTRACT
BACKGROUND AND AIMS: Low GLP-1 has been implicated in obesity and type 2 diabetes. Some studies reported reduced post-prandial GLP-1 levels in type 2 diabetics, whereas others reported GLP-1 levels not reduced in patients with impaired glucose tolerance (IGT) or type 2 diabetes. We undertook this study to evaluate the effect of obesity and pre-diabetes on GLP-1 levels in response to 75 g oral glucose. METHODS: Eighty subjects comprised four groups: 20 control subjects (normal weight and normal glucose tolerance (NGT)), 20 obese with NGT, 20 obese with impaired fasting glucose (IFG) and 20 obese with both IFG and impaired glucose tolerance (IGT). Laboratory tests included fasting blood glucose (FBG), 75 g glucose OGTT, fasting insulin and glucose-stimulated GLP-1 (30 min after 75 g glucose). Insulin resistance was quantified using HOMA-IR. RESULTS: GLP-1 levels were significantly decreased in obese subjects compared to controls (571.17 ± 170.37 vs. 908.50 ± 169.90 pg/mL, p <0.001) and it was negatively correlated with body mass index (BMI) and waist circumference in all studied groups. Levels of GLP-1 were negatively correlated with HOMA-IR in all obese groups (r = -0.75, p <0.001). No significant difference was found in GLP-1 levels between all obese subjects (611.50 ± 187.96, 577.50 ± 150.85, 524.50 ± 167.35 pg/mL respectively, p >0.05). Morbidly obese cases (n = 15) had a significantly higher fasting insulin (25.20 ± 2.49 vs. 14 ± 3.81 µIU/ml), higher HOMA-IR (6.69 ± 1.2 vs. 3.48 ± 1.20), and lower GLP- 1 (212.0 ± 35.64 vs. 603.82 ± 136.35 pg/mL) (p <0.001) compared to non-morbid obese cases (n = 45). CONCLUSIONS: Obesity reduces the GLP-1 levels. In insulin resistance, GLP-1 levels were reduced and it was related to the degree of insulin resistance.
