Tu2012 Impact of a 2-Week Very Low Calorie Diet (VLCD) on Glucose Sensing, Absorption, Transporters, Incretin Hormones and Glycemia in Morbidly Obese Humans

We showed that glucose absorption is accelerated in the proximal intestine of morbidly obese humans, associated with increased expression of sodium dependent glucose co-transporter 1 (SGLT1), an altered incretin profile, hyperinsulinemia and hyperglycemia.This study aimed to examine the effects of energy restriction on glucose absorption, expression of intestinal glucose transporters and sweet taste receptors (STR), incretin hormone responses and glycemia in the morbidly obese.Methods: 10 non-diabetic, morbidly obese subjects (2M:8F; 45±3yrs, BMI: 46±3kg/m2) were studied before and after a 2-week VLCD (750kcal/day).On each occasion, endoscopic duodenal biopsies were collected before and after intraduodenal glucose infusion (30g glucose over 30 min, with 3g 3-O-methylglucose (3-OMG) to estimate glucose absorption).Blood glucose and plasma concentrations of 3-OMG, glucosedependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and insulin were measured over 240 min.Absolute expression of SGLT-1, GLUT2 and STR (T1R2) transcripts was quantified by PCR.Results After 2 weeks of VLCD, body weight (-5.6±0.5kg,P<0.001), HbA1c (-0.32±0.08%,P=0.001), fasting blood glucose (-0.5±0.1mmol/L,P=0.02) and fasting expression of T1R2 (-54±22%, P=0.03), SGLT1 (-30±7%, P=0.004) and GLUT2 (-50±15%, P=0.008) were lower than at baseline.Prior to VLCD, intra-duodenal glucose had no impact onT1R2, SGLT-1 and GLUT2 expression, but after VLCD, intra-duodenal glucose stimulated increased expression of T1R2 (45±30%, P=0.03) and GLUT2 (57±14%, P=0.003).The blood glucose (P=0.002),plasma GIP (P=0.03) and plasma insulin (P=0.002)responses to intra-duodenal glucose were all reduced after VLCD, while plasma 3-OMG and GLP-1 concentrations were unchanged.CONCLUSIONS: The improvement in glycemic control after short-term VLCD in morbid obesity is most likely mediated by reduced insulin resistance from weight loss, but not via a reduction in intestinal glucose absorption or an increased incretin response.Although VCLD reduces the fasting expression of both STR and glucose transporters, these increase rapidly on exposure to glucose.Further studies with inhibitors of STR and/or glucose transporters are warranted to determine whether the changes in receptor expressional dynamics are responsible for the observed incretin responses.