This review analyses the effect of beta-glucan, a soluble fiber found in oat bran and barley, on the viscosity of the meal bolus in the small intestine. A high viscosity can delay glucose absorption. A concentration of 10% beta-glucan in a cereal food can achieve a 50% reduction of the glycemic peak. A daily intake of beta-glucan of at least 3 g of beta-glucan can also cause a significant lowering effect on plasma cholesterol.