Inhibitory Effect of Calcium Alginate on Postprandial Blood Glucose Elevation (JCTR)
Diabetes is known to increase the risk of myocardial and cerebral infarction, as well as complications such as retinopathy, nephropathy and neuropathy. It is important for diabetics to improve their eating habits, for example, by eating slowly, avoiding overeating, and increasing their intake of vegetables, in order to suppress sudden rises in blood glucose (Glu) levels. On the other hand, alginic acid (Alg), which is a polysaccharide derived from brown algae, is used as a food and medicinal additive, a health food and a pharmaceutical, based on its blood cholesterol-lowering effect and protective effect on the gastric mucosa. It was recently reported that calcium alginate (Ca-Alg) has the pharmacological effect of suppressing blood Glu elevation. We investigated the mechanism of this effect and found that Ca-Alg inhibits the metabolism of starch in the gastrointestinal tract by inhibiting the activity of α-glucosidase, which degrades maltose into Glu.We also examined the influence of the amount of Ca-Alg added to the diet and the particle size of the Ca-Alg on postprandial blood Glu elevation in rats. Subsequently, we conducted several clinical trials. We asked healthy adults to eat udon noodles, soba (buckwheat noodles), and Chinese noodles containing CaAlg, and measured the blood Glu levels after consumption. In each case, Ca-Alg decreased blood Glu levels and suppressed total absorption of Glu. This review summarizes the results of our basic and clinical studies on the effects of Ca-Alg on postprandial blood Glu elevation.
In recent years, the number of people with lifestyle-related diseases has increased dramatically [1,2]. In particular, the incidences of diabetes, hypertension, and dyslipidemia are increasing, and these diseases increase the risks of cancer, heart disease, and cerebrovascular disease, which are leading causes of death in developed countries [3-10]. For example, diabetes increases the risks of myocardial and cerebral infarction, as well as complications such as retinopathy, nephropathy and neuropathy [11,12]. Unfortunately, diabetes is often diagnosed late, because its initial symptoms are subjective, so prevention is very important.
Glucose (Glu) is absorbed from the gastrointestinal tract, and enters the systemic circulation. It is then taken up by muscle, fat, and other tissues via the action of insulin secreted from the pancreas, and is used or stored as an energy source. Type-2 diabetes is caused by the retention of Glu in the blood due to the impaired action of insulin [13,14]. One approach to prevent diabetes is to improve people’s eating and exercise habits. The purpose of improving eating habits, for example, by eating slowly, avoiding overeating, and increasing intake of vegetables, is to suppress sudden rises in blood Glu levels . Alginic acid (Alg) is a polysaccharide derived from brown algae, such as kelp and seaweed. Alg and its salts (calcium alginate (CaAlg), sodium alginate (Na-Alg), ammonium alginate, and potassium alginate) are non-toxic; their daily tolerable intake is described as "not specified" by the Ministry of Health, Labor and Welfare, Japan . Na-Alg is used as a food additive (thickening stabilizer) and medicinal additive, and also as a health food and pharmaceutical, because it has a blood cholesterol-lowering effect and a protective effect on the gastric mucosa . However, chronic high intake of sodium is among the risk factors for hypertension . Therefore, Ca-Alg might be preferable to Na-Alg, if its cholesterol-lowering effect is equal to or greater than that of Na-Alg. Ca-Alghas a wide range of beneficial biological effects. We have shown that Ca-Alg promotes the excretion of heavy metals such as strontium and cesium in rats, and we examined the mechanism involved [19,20]. We found that Ca-Alg inhibits the reabsorption of bile acids in the gastrointestinal tract and promotes their excretion into feces in rats, thereby promoting catabolism of cholesterol to bile acids in the liver and resulting in a decrease of blood cholesterol . We also showed that CaAlg inhibits the absorption of triglyceride (lipid) from food by forming large micelles with triglyceride as their core . It has also been suggested that Ca-Alg suppresses blood Glu elevation . We were interested in this action, and investigated the effect of Ca-Alg in rats, focusing on the influence of the particle size of Ca-Alg and the amount of CaAlg added to the diet . We subsequently carried out clinical trials in which healthy adults were asked to consume various foods, i.e., udon noodles , soba (buckwheat noodles) , and Chinese noodles  containing Ca-Alg, and we measured their changes of blood Glu levels. Here we review the results of these experimental studies and clinical trials, and summarize the effects of Ca-Alg on postprandial blood Glu elevation.
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Journal of Clinical Trials