A whey/guar "preload" improves postprandial glycaemia and glycated haemoglobin levels in type 2 diabetes: A 12-week, single-blind, randomized, placebo-controlled trial.

AIMS: To evaluate the effects of 12 weeks of treatment with a whey/guar preload on gastric emptying, postprandial glycaemia and glycated haemoglobin (HbA1c) levels in people with type 2 diabetes (T2DM). MATERIALS AND METHODS: A total of 79 people with T2DM, managed on diet or metformin (HbA1c 49 ± 0.7 mmol/mol [6.6 ± 0.1%]), were randomized, in single-blind fashion, to receive 150 mL flavoured preloads, containing either 17 g whey protein plus 5 g guar (n = 37) or flavoured placebo (n = 42), 15 minutes before two meals, each day for 12 weeks. Blood glucose and gastric emptying (breath test) were measured before and after a mashed potato meal at baseline (without preload), and after the preload at the beginning (week 1) and end (week 12) of treatment. HbA1c levels, energy intake, weight and body composition were also evaluated. RESULTS: Gastric emptying was slower (P < 0.01) and postprandial blood glucose levels lower (P < 0.05) with the whey/guar preload compared to placebo preload, and the magnitude of reduction in glycaemia was related to the rate of gastric emptying at both week 1 (r = -0.54, P < 0.001) and week 12 (r = -0.54, P < 0.0001). At the end of treatment, there was a 1 mmol/mol [0.1%] reduction in HbA1c in the whey/guar group compared to the placebo group (49 ± 1.0 mmol/mol [6.6 ± 0.05%] vs. 50 ± 0.8 mmol/mol [6.7 ± 0.05%]; P < 0.05). There were no differences in energy intake, body weight, or lean or fat mass between the groups. CONCLUSIONS: In patients with well-controlled T2DM, 12 weeks' treatment with a low-dose whey/guar preload, taken twice daily before meals, had sustained effects of slowing gastric emptying and reducing postprandial blood glucose, which were associated with a modest reduction in HbA1c, without causing weight gain.

Changes in meal composition and duration affect postprandial endothelial function in healthy humans.

Endothelial function, measured by flow-mediated dilatation (FMD), predicts cardiovascular events and is impaired postprandially. The objective of this study was to evaluate the effects of changes in composition or duration of ingestion of a meal, which slows gastric emptying and/or small intestinal nutrient exposure, on postprandial endothelial function. Twelve healthy subjects (6 male, 6 female; 33 ± 6 yr) were each studied on three occasions, in a randomized crossover design. After an overnight fast, subjects consumed a [(13)C]octanoic acid-labeled mashed potato meal ("meal 1"), or meal 1 mixed with 9 g guar ("meal 2") within 10 min, or meal 1 divided into 12 equal portions over 60 min ("meal 3"). Brachial artery FMD was measured every 30 min for 120 min. Blood glucose, serum insulin, and gastric emptying (breath test) were evaluated for 240 min. Data are means ± SE. Compared with meal 1, meal 2 was associated with slower gastric emptying (half-emptying time 285 ± 27 vs. 208 ± 15 min, P < 0.05), lower postprandial blood glucose and insulin (P < 0.001 for both), and a delayed, but more sustained, suppression of FMD (P < 0.001). After meal 3, both glycemic increment and reduction in FMD were less than after meal 2 (P < 0.05 for both). The decrement in FMD was directly related to the increment in blood glucose (r = 0.46, P = 0.02). We conclude that, in health, postprandial FMD is influenced by perturbation of gastric emptying and the duration of meal consumption, which also impact on glycemia.

Effect of the artificial sweetener, sucralose, on small intestinal glucose absorption in healthy human subjects.

It has been reported that the artificial sweetener, sucralose, stimulates glucose absorption in rodents by enhancing apical availability of the transporter GLUT2. We evaluated whether exposure of the proximal small intestine to sucralose affects glucose absorption and/or the glycaemic response to an intraduodenal (ID) glucose infusion in healthy human subjects. Ten healthy subjects were studied on two separate occasions in a single-blind, randomised order. Each subject received an ID infusion of sucralose (4 mM in 0.9% saline) or control (0.9% saline) at 4 ml/min for 150 min (T = - 30 to 120 min). After 30 min (T = 0), glucose (25 %) and its non-metabolised analogue, 3-O-methylglucose (3-OMG; 2.5 %), were co-infused intraduodenally (T = 0-120 min; 4.2 kJ/min (1 kcal/min)). Blood was sampled at frequent intervals. Blood glucose, plasma glucagon-like peptide-1 (GLP-1) and serum 3-OMG concentrations increased during ID glucose/3-OMG infusion (P < 0.005 for each). However, there were no differences in blood glucose, plasma GLP-1 or serum 3-OMG concentrations between sucralose and control infusions. In conclusion, sucralose does not appear to modify the rate of glucose absorption or the glycaemic or incretin response to ID glucose infusion when given acutely in healthy human subjects.

Acute effects of the glucagon-like peptide-1 receptor agonist, exenatide, on blood pressure and heart rate responses to intraduodenal glucose infusion in type 2 diabetes.

AIM: To evaluate the effects of the glucagon-like peptide-1 receptor agonist, exenatide, on blood pressure and heart rate during an intraduodenal glucose infusion in type 2 diabetes. METHODS: Nine subjects with type 2 diabetes were randomised to receive intravenous exenatide or saline control in a crossover design. Glucose (3 kcal min-1) was infused via an intraduodenal manometry catheter for 60 min. Blood pressure, heart rate, and the frequency and amplitude of duodenal pressure waves were measured at regular intervals. Gastrointestinal symptoms were monitored using 100 mm visual analogue scales. RESULTS: During intraduodenal glucose infusion (0-60 min), diastolic (p(0-60) = 0.03) and mean arterial (p(0-60) = 0.03) blood pressures and heart rate (p(0-60) = 0.06; p(0-120) = 0.03)) were higher with exenatide compared to placebo. The increase in the area under the curve for diastolic blood pressure and mean arterial blood pressure was related directly to the suppression of the duodenal motility index with exenatide compared to control (p = 0.007 and 0.04, respectively). CONCLUSION: In type 2 diabetes, intravenous exenatide increases mean arterial blood pressure and heart rate during an intraduodenal glucose infusion, supporting the need for further research with exenatide for its potential use in postprandial hypotension.

Administration of resveratrol for 5 wk has no effect on glucagon-like peptide 1 secretion, gastric emptying, or glycemic control in type 2 diabetes: a randomized controlled trial.

BACKGROUND: Resveratrol has been reported to lower glycemia in rodent models of type 2 diabetes associated with the stimulation of glucagon-like peptide 1 (GLP-1), which is known to slow gastric emptying, stimulate insulin secretion, and suppress glucagon secretion and energy intake. OBJECTIVE: We evaluated the effects of 5 wk of resveratrol treatment on GLP-1 secretion, gastric emptying, and glycemic control in type 2 diabetes. DESIGN: Fourteen patients with diet-controlled type-2 diabetes [mean ± SEM glycated hemoglobin (HbA1c): 6.4 ± 0.2% (46.4 ± 2.2 mmol/mol)] received resveratrol (500 mg twice daily) or a placebo over two 5-wk intervention periods with a 5-wk washout period in between in a double-blind, randomized, crossover design. Before and after each intervention period (4 visits), body weight and HbA1c were measured, and patients were evaluated after an overnight fast with a standardized mashed-potato meal labeled with 100 µg (13)C-octanoic acid to measure blood glucose and plasma GLP-1 concentrations and gastric emptying (breath test) over 240 min. Daily energy intake was estimated from 3-d food diaries during the week before each visit. RESULTS: Fasting and postprandial blood glucose and plasma total GLP-1 as well as gastric emptying were similar at each assessment, and the change in each variable from weeks 0 to 5 did not differ between resveratrol and placebo groups. Similarly, changes in HbA1c, daily energy intake, and body weight after 5 wk did not differ between the 2 treatments. CONCLUSIONS: In patients with diet-controlled type 2 diabetes, 5 wk of twice-daily 500 mg-resveratrol supplementation had no effect on GLP-1 secretion, glycemic control, gastric emptying, body weight, or energy intake. Our observations do not support the use of resveratrol for improving glycemic control. This trial was registered at www.anzctr.org.au as ACTRN12613000717752.

Effects of intraduodenal hydroxycitrate on glucose absorption, incretin release, and glycemia in response to intraduodenal glucose infusion in health and type 2 diabetes: A randomised controlled trial.

OBJECTIVE: Hydroxycitric acid (HCA), derived from the fruit Garcinia cambogia, reduces the rate of glucose absorption and lowers postprandial glycemia in rodents, but its effect in humans is unknown. The aim of this study was to investigate the effects of small intestinal perfusion with HCA on glucose absorption, as well as the incretin and glycemic responses to a subsequent intraduodenal glucose infusion, in both healthy individuals and patients with type 2 diabetes. METHODS: Twelve healthy participants and 8 patients with type 2 diabetes received an intraduodenal infusion of HCA (2800 mg in water) or control (water) over 60 min, followed by an intraduodenal infusion of 60 g glucose over 120 min, in a double-blind, randomized crossover design. In healthy individuals, 5 g 3-O-methylglucose (3-OMG) was co-infused with glucose as a marker of glucose absorption. Blood was sampled frequently. RESULTS: In healthy individuals, blood glucose was lower with HCA than control, both before and during the intraduodenal glucose infusion (P < 0.05 for each). Plasma glucose-dependent insulinotropic polypeptide (GIP; P = 0.01) and glucagon (P = 0.06) were higher with HCA, but there were no differences in plasma glucagon-like peptide (GLP)-1, insulin, or serum 3-OMG concentrations. In patients with type 2 diabetes, blood glucose, and plasma GIP, GLP-1, and insulin did not differ between HCA and control either before or after intraduodenal glucose, but during glucose infusion, plasma glucagon was higher with HCA (P = 0.04). CONCLUSION: In healthy individuals, small intestinal exposure to HCA resulted in a modest reduction in glycemia and stimulation of plasma GIP and glucagon, but no effect on plasma GLP-1 or insulin, or on glucose absorption. HCA had no effect on glycemia in patients with type 2 diabetes.

The Glucagon-Like Peptide 1 Receptor Agonist Exenatide Inhibits Small Intestinal Motility, Flow, Transit, and Absorption of Glucose in Healthy Subjects and Patients With Type 2 Diabetes: A Randomized Controlled Trial.

The short-acting glucagon-like peptide 1 receptor agonist exenatide reduces postprandial glycemia, partly by slowing gastric emptying, although its impact on small intestinal function is unknown. In this study, 10 healthy subjects and 10 patients with type 2 diabetes received intravenous exenatide (7.5 µg) or saline (-30 to 240 min) in a double-blind randomized crossover design. Glucose (45 g), together with 5 g 3-O-methylglucose (3-OMG) and 20 MBq (99m)Tc-sulfur colloid (total volume 200 mL), was given intraduodenally (t = 0-60 min; 3 kcal/min). Duodenal motility and flow were measured using a combined manometry-impedance catheter and small intestinal transit using scintigraphy. In both groups, duodenal pressure waves and antegrade flow events were fewer, and transit was slower with exenatide, as were the areas under the curves for serum 3-OMG and blood glucose concentrations. Insulin concentrations were initially lower with exenatide than with saline and subsequently higher. Nausea was greater in both groups with exenatide, but suppression of small intestinal motility and flow was observed even in subjects with little or no nausea. The inhibition of small intestinal motor function represents a novel mechanism by which exenatide can attenuate postprandial glycemia.

Effects of different sweet preloads on incretin hormone secretion, gastric emptying, and postprandial glycemia in healthy humans.

BACKGROUND: Macronutrient "preloads" can stimulate glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), slow gastric emptying, and reduce postprandial glycemic excursions. After sweet preloads, these effects may be signaled by sodium-glucose cotransporter-1 (SGLT1), sweet taste receptors, or both. OBJECTIVE: We determined the effects of 4 sweet preloads on GIP and GLP-1 release, gastric emptying, and postprandial glycemia. DESIGN: Ten healthy subjects were studied on 4 separate occasions each. A preload drink containing 40 g glucose, 40 g tagatose/isomalt mixture (TIM), 40 g 3-O-methylglucose (3OMG; a nonmetabolized substrate of SGLT1), or 60 mg sucralose was consumed 15 min before a (13)C-octanoic acid-labeled mashed potato meal. Blood glucose, plasma total GLP-1 and GIP, serum insulin, and gastric emptying were determined. RESULTS: Both glucose and 3OMG stimulated GLP-1 and GIP release in advance of the meal (each P < 0.05), whereas TIM and sucralose did not. The overall postprandial GLP-1 response was greater after glucose, 3OMG, and TIM than after sucralose (P < 0.05), albeit later after TIM than the other preloads. The blood glucose and insulin responses in the first 30 min after the meal were greatest after glucose (each P < 0.05). Gastric emptying was slower after both 3OMG and TIM than after sucralose (each P < 0.05). CONCLUSIONS: In healthy humans, SGLT1 substrates stimulate GLP-1 and GIP and slow gastric emptying, regardless of whether they are metabolized, whereas the artificial sweetener sucralose does not. Poorly absorbed sweet tastants (TIM), which probably expose a greater length of gut to nutrients, result in delayed GLP-1 secretion but not in delayed GIP release. These observations have the potential to optimize the use of preloads for glycemic control. This trial was registered at www.actr.org.au as ACTRN12611000775910.