Increasing oat β-glucan viscosity in a breakfast meal slows gastric emptying and reduces glycemic and insulinemic responses but has no effect on appetite, food intake, or plasma ghrelin and PYY responses in healthy humans: a randomized, placebo-controlled, crossover trial

Background The viscosity of oat β-glucan (OBG) determines its effect on serum cholesterol and glycemic responses, but whether OBG viscosity affects gastric emptying, appetite, and ad libitum food intake is unknown. Objectives We aimed to determine the effect of altering the amount or molecular weight (MW) and, hence, viscosity of OBG in a breakfast meal on the primary endpoint of food intake at a subsequent meal. Methods Overnight-fasted males (n = 16) and nonpregnant females (n = 12) without diabetes, aged 18-60 y, with BMI 20.0-30.0 kg/m² who were unrestrained eaters participated in a double-blind, randomized, crossover study at a contract research organization. Participants consumed, in random order, breakfast meals equivalent in weight, energy, and macronutrients consisting of white-bread, butter, jam, and 2% milk plus hot cereal [Cream of Rice (CR), or instant-oatmeal plus either 3 g oat-bran (2gOBG), 10 g oat-bran (4gOBG), or 10 g oat-bran plus β-glucanase (4gloMW) to reduce OBG MW and viscosity compared with 4gOBG]. Gastric emptying, subjective appetite, and glucose, insulin, ghrelin, and peptide tyrosine tyrosine (PYY) responses were assessed for 3 h and then subjects were offered an ad libitum lunch (water and pizza). Results Pizza intakes (n = 28) after CR, 2gOBG, 4gOBG, and 4gloMW (mean ± SEM: 887 ± 64, 831 ± 61, 834 ± 78, and 847 ± 68 kcal, respectively) were similar (nonsignificant). Compared with CR, 4gOBG significantly reduced glucose (78 ± 10 compared with 135 ± 15 mmol × min/L) and insulin (14.0 ± 1.6 compared with 26.8 ± 3.5 nmol × min/L) incremental area-under-the-curve and delayed gastric-emptying half-time (geometric mean: 285; 95% CI: 184, 442, compared with geometric mean: 105; 95% CI: 95, 117 min), effects not seen after 4gloMW. Subjective appetite, PYY, and ghrelin responses after 2gOBG, 4gOBG, and 4gloMW were similar to those after CR. Conclusions The results demonstrate that OBG viscosity determines its effect on postprandial glucose, insulin, and gastric emptying. However, we were unable to demonstrate a significant effect of OBG on appetite or food intake, regardless of its viscosity.This trial was registered at clinicaltrials.gov as NCT03490851.