Abstract
BackgroundResistant glucan (RG) and hydrogenated resistant glucan (HRG) are new dietary fiber materials developed to decrease the risk of metabolic syndrome and lifestyle-related diseases. We investigated the metabolism and bioavailability of RG and HRG using rats and humans.MethodsPurified RG and HRG were used as test substances. After 25 Wistar male rats (270 g) were fed with an experimental diet (AIN93M diet with the cellulose replaced by β-corn starch) ad libitum for 1 week, they were used for the experiment involving blood collection and circulating air collection. Ten participants (5 males, 22.5 y, BMI 20.4 kg/m2; 5 females, 25.8 y, BMI 20.9 kg/m2) voluntarily participated in this study. The study was carried out using a within-subject, repeated measures design. Effects of RG and HRG on the response for blood glucose and insulin and hydrogen excretion were compared with those of glucose and a typical nondigestible and fermentable fructooligosaccharide (FOS) in rats and humans. Available energy was evaluated using the fermentability based on breath hydrogen excretion.ResultsWhen purified RG or HRG (400 mg) was administered orally to rats, blood glucose and insulin increased slightly, but less than when glucose was administration (P < 0.05). Hydrogen started to be excreted 120 min after administration of RG with negligibly small peak at 180 min, thereafter excreted scarcely until 1440 min. Hydrogen excretion after HRG administration showed a larger peak than RG at 180 min, but was markedly less than FOS. RG and HRG were excreted in feces, but not urine. When purified RG or HRG (30 g) were ingested by healthy humans, blood glucose and insulin levels increased scarcely. Breath hydrogen excretion increased slightly, but remarkably less than FOS. Ingestion of purified RG or HRG (5 g) to evaluate available energy, increased scarcely glucose and insulin levels and breath hydrogen excretion. Available energy was evaluated as 0 kcal/g for purified RG and 1 kcal/g for HRG.ConclusionThe bioavailability was very low in both humans and rats, because oligosaccharide of minor component in purified RG and HRG was metabolized via intestinal microbes but major components with higher molecular weight were metabolized scarcely. Moreover, the ingestion of 30 g of RG or HRG did not induce apparent acute side effects in healthy adults. RG and HRG might potentially be used as new dietary fiber materials with low energy.
Highlights
Resistant glucan (RG) and hydrogenated resistant glucan (HRG) are new dietary fiber materials developed to decrease the risk of metabolic syndrome and lifestyle-related diseases
The response of plasma glucose and insulin after administration of RG, HRG and resistant maltodexitrin (RMD) were significantly lower than those of the administration of glucose (P < 0.05). These results suggest that when RG and HRG are given orally to rats, they are partially hydrolyzed by gastrointestinal enzymes and cause similar increases in blood glucose and insulin levels
In the present study we investigated the metabolism and bioavailability of RG and HRG using rats and healthy human subjects, thereafter we estimated that the available energy was 0 kcal/g for purified RG and 1 kcal/g for HRG in healthy humans, respectively
Summary
Resistant glucan (RG) and hydrogenated resistant glucan (HRG) are new dietary fiber materials developed to decrease the risk of metabolic syndrome and lifestyle-related diseases. We investigated the metabolism and bioavailability of RG and HRG using rats and humans. In order to use widely RG and HRG as food materials, it is necessary to clarify the physiological effects of RG and HRG on the response for blood glucose and insulin, the occurrence of abdominal symptoms, the maximum non-effective dose for osmotic diarrhea, fermentability by intestinal microbes and metabolic fate. We have already proposed the indirect and simple method to evaluate the available energy of dietary fiber materials in healthy humans [4,5,6]. The metabolism and bioavailability of RG and HRG were investigated using rats and healthy human subjects and the available energy for purified RG and HRG was estimated by our proposed method
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