Title: Differentiating the effects of whey protein and guar gum preloads on postprandial glycemia in type 2 diabetes

Background and aims: Whey protein and guar gum have both been reported to reduce postprandial glycemia in health and type 2 diabetes, associated with stimulation of glucagon-like peptide-1 (GLP-1) and/or slowing of gastric emptying. Our aim was to evaluate, in type 2 diabetes, the acute effects of low dose preloads of whey and guar, given alone or in combination before a meal, on postprandial glycemia, insulin, GLP-1, and gastric emptying. Methods: 21 patients with type 2 diabetes, managed by diet or metformin alone, were each studied on 4 days. They received a preload shake 15min before a mashed potato meal (368.5 kcal) labeled with C-13-octanoic-acid. The preloads comprised either (i) 17 g whey (W), (ii) 5 g guar (G), (iii) 17 g whey + 5 g guar (WG) each sweetened with 60 mg sucralose, and (iv) 60 mg sucralose alone (control; C), all dissolved in 150 mL water. Venous blood was sampled frequently for measurements of glucose, insulin, and GLP-1 concentrations. Gastric half-emptying time (T50) was calculated from breath (CO2)-C-13 excretion over 240 min. Results: Postprandial blood glucose concentrations were lower with W and WG compared to C (each P < 0.0001, treatment x time interaction), and lower after G than C only at 30min. Insulin, GLP-1, and glucagon concentrations were higher after W than WG, G, or C (P < 0.05, treatment x time interaction), without differences between the latter three. Gastric emptying was slower with W (T50: 179.6 +/- 6.1 min, P < 0.05) and WG (T50: 197.6 +/- 9.7 min, P < 0.0001) when compared to C (T50: 162.9 +/- 6.2 min), but did not differ between G (T50: 171.3 +/- 7.0) and C (P > 0.99). Conclusion: Both whey and whey/guar preloads reduced postprandial glycemia, associated with slowing of gastric emptying. Low dose guar was less effective as a preload for glucose-lowering and did not slow gastric emptying. (C) 2018 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.