Total fibre vs types and sources of fibre in subjects with and without diabetes: Role of molecular weight and viscosity

Abstract

Dietary fibre is an important short-fall nutrient with average intakes in North America being only 50–67% of recommended. Food fortification or fibre supplements could help fill the gap, but what sources/types of fibre should be recommended? This paper addresses the role of fibre viscosity on blood-glucose and -lipids in humans. The postprandial glycaemic response (PPGR) of healthy adults after test-meals containing oat β-glucan (OBG) is inversely related to OBG viscosity, which, in turn, is determined by OBG dose and molecular weight (MW). A systematic-review and meta-analysis (SRMA) showed that OBG dose and MW significantly influenced the effect of OBG on PPGR. Indeed, 10–15 times more medium-MW (300–1000 kDa) or low-MW (<300 kDa) OBG was required to reduce PPGR compared to 0.2 g/30 g available-carbohydrate for high-MW OBG (>1000 kDa). Studies also suggest that MW determines the effect of OBG on serum-cholesterol. The effects of fibre in diabetes were assessed by an umbrella review of published SMRA. All fibre types reduced HbA1c by (mean [95% confidence interval]) −0.37 [-0.51, −0.22]% (n = 74), fasting-glucose by −0.70 [-0.95, −0.45] mmol/L (n = 74) and serum-cholesterol by −0.33 [-0.49, −0.16] mmol/L (n = 38), but the effects differed by fibre type and source. Non-viscous fibres elicited statistically but not clinically significant reductions in HbA1c (−0.17 [-0.30, −0.04]%) and fasting-glucose (−0.35 [-0.60, −0.11] mmol/L), whereas viscous fibres elicited statistically and clinically significant reductions in HbA1c (−0.57 [-0.87, −0.27]%), fasting-glucose (−1.00 [-1.42, −0.58] mmol/L) and LDL-cholesterol (−0.34 [-0.62, −0.06] mmol/L). Is it time to reconsider the use of viscous fibre supplements in the treatment of diabetes?