Increasing the viscosity of oat β-glucan beverages by reducing solution volume does not reduce glycaemic responses

The soluble fibre (1 -> 3)(1 -> 4)-beta-D-glucan attenuates postprandial glycaemic responses when administered in solution. This attenuating effect is strengthened when solution viscosity is increased by increasing the beta-glucan dose or molecular weight (MW). The effect of varying solution viscosity by changing solution volume, without changing the beta-glucan dose or MW, on glycaemic responses was determined. A total of fifteen healthy subjects received six 50 g oral glucose beverages prepared with or without 4 g of high-MW (HMW, 580 000 g/mol) or low-MW (LMW, 145 000 g/mol) beta-glucan, with a beverage volume of 250 or 600 ml. Postprandial plasma glucose concentration was measured over 2 h, and the peak blood glucose rise (PBGR) and the incremental area under the glycaemic response curve (AUC) were calculated. Subjects served as their own controls. The physico-chemical properties of the beverages were measured to examine their relationship with glycaemic response results. The HMW beta-glucan beverage was more viscous and achieved greater reductions in PBGR than the glucose beverage with LMW beta-glucan (P<0.05). At the same MW, the 250 and 600 ml beta-glucan beverages differed in viscosity (>9-fold difference) but not in PBGR (P>0.05). No differences in AUC were detected among the beverages (P=0.147). The effects of beta-glucan on glycaemic response were altered by changes in beverage viscosity achieved through changes in MW but not in volume. Therefore, beta-glucan dose and MW are the most vital characteristics for optimising the bioactivity of beta-glucan solutions with respect to glycaemic response.