Calcium alginate (Ca-Alg) is known to suppress the postprandial increase of blood glucose, and therefore may be helpful for preventing lifestyle-related diseases such as diabetes. In this work, we examined the mechanism of this effect. As α-amylase activity and α-glucosidase activity are involved in the digestion of starch, we examined the in vitro inhibitory effect of Ca-Alg on these enzymes. Ca-Alg showed little inhibition of α-amylase, but markedly inhibited α-glucosidase activity. The direct binding affinity of glucose for Ca-Alg was low. Also, Ca-Alg had essentially no effect on the membrane permeability of glucose. Therefore, we considered that the suppression of blood glucose by Ca-Alg is predominantly due to a decrease in the efficiency of starch digestion as a result of inhibition of α-glucosidase, possibly due to increased viscosity of the gastrointestinal contents. Next, we investigated the optimum amount in the diet and the optimum particle size of Ca-Alg for suppressing postprandial blood glucose level in rats orally administered a diet containing starch with various amounts and particle sizes of Ca-Alg. We found that 5% by weight of 270-mesh-pass Ca-Alg was most effective.
