A study was conducted to determine which dietary fibre or fibre analogue is most effective in reducing postprandial hyperglycaemia in diabetics. Four to six volunteers underwent 50-g glucose tolerance tests (GTT) with and without the addition of various fibres, including guar, pectin, gum tragacanth, methylcellulose, wheat bran, or cholestyramine. The addition of each substance significantly reduced blood glucose and serum insulin concentrations. Guar was the most effective in flattening the glucose response, but this effect was abolished when hydrolysed non-viscous guar was used. The reduction in blood glucose peak concentration correlated positively with the viscosity of the substance (r = 0.926; P < 0.01) and with the delay in mouth-to-caecum transit time (r = 0.885; P < 0.02). Viscous dietary fibres were found to be most effective in reducing postprandial hyperglycaemia. The study showed that viscosity is a key factor in the effectiveness of dietary fibres in reducing blood glucose and insulin concentrations. Guar, the most viscous substance, was the most effective in decreasing postprandial glucose and insulin concentrations. This was confirmed by the fact that hydrolysis of guar destroyed its viscous character and thus its effectiveness. Other viscous agents, such as tragacanth, pectin, and cholestyramine, also reduced postprandial glucose concentrations, although cholestyramine's effect was not explained by viscosity. The study concluded that viscosity is the most important property of dietary fibre related to its ability to reduce postprandial glycaemia. Agents that increase viscosity provide a promising approach to the treatment of diabetes. The results suggest that high-viscosity fibres, such as guar, are more effective in reducing postprandial glucose concentrations than other fibres, such as wheat bran or apple fibre. Guar, tragacanth, and pectin are already used as thickeners in the food industry and are important dietary fibres. Methycellulose, although a bulking agent, has little effect on glucose tolerance due to its low viscosity. Cholestyramine, which reduces postprandial blood sugar concentration, does not appear to be related to viscosity. The study highlights the importance of viscosity in the effectiveness of dietary fibres in reducing postprandial glycaemia.A study was conducted to determine which dietary fibre or fibre analogue is most effective in reducing postprandial hyperglycaemia in diabetics. Four to six volunteers underwent 50-g glucose tolerance tests (GTT) with and without the addition of various fibres, including guar, pectin, gum tragacanth, methylcellulose, wheat bran, or cholestyramine. The addition of each substance significantly reduced blood glucose and serum insulin concentrations. Guar was the most effective in flattening the glucose response, but this effect was abolished when hydrolysed non-viscous guar was used. The reduction in blood glucose peak concentration correlated positively with the viscosity of the substance (r = 0.926; P < 0.01) and with the delay in mouth-to-caecum transit time (r = 0.885; P < 0.02). Viscous dietary fibres were found to be most effective in reducing postprandial hyperglycaemia. The study showed that viscosity is a key factor in the effectiveness of dietary fibres in reducing blood glucose and insulin concentrations. Guar, the most viscous substance, was the most effective in decreasing postprandial glucose and insulin concentrations. This was confirmed by the fact that hydrolysis of guar destroyed its viscous character and thus its effectiveness. Other viscous agents, such as tragacanth, pectin, and cholestyramine, also reduced postprandial glucose concentrations, although cholestyramine's effect was not explained by viscosity. The study concluded that viscosity is the most important property of dietary fibre related to its ability to reduce postprandial glycaemia. Agents that increase viscosity provide a promising approach to the treatment of diabetes. The results suggest that high-viscosity fibres, such as guar, are more effective in reducing postprandial glucose concentrations than other fibres, such as wheat bran or apple fibre. Guar, tragacanth, and pectin are already used as thickeners in the food industry and are important dietary fibres. Methycellulose, although a bulking agent, has little effect on glucose tolerance due to its low viscosity. Cholestyramine, which reduces postprandial blood sugar concentration, does not appear to be related to viscosity. The study highlights the importance of viscosity in the effectiveness of dietary fibres in reducing postprandial glycaemia.