Resistant maltodextrin (RMD) from various sources of starch has been extensively studied. However, studies which reported the effects of tapioca RMD (TRM) on glucose and insulin response are lacking. This study investigated the effect of TRM on postprandial plasma glucose and serum insulin in healthy subjects. Additionally, satiety and gastrointestinal tolerability were also evaluated. Sixteen healthy participants received five different treatments on five separate days. Participants received 50 g of either: glucose (GL), tapioca maltodextrin (TM), TRM, MIX15% (7⋅5 g TRM + 42⋅5 g TM) or MIX50% (25 g TRM + 25 g TM). Plasma glucose, serum insulin and subjective appetite responses were measured postprandially over 180 min. Gastrointestinal symptoms were evaluated by questionnaire before and after each test day. Results showed that at 30 min after treatment drinks, plasma glucose after TRM was significantly lowest (104⋅60 (sem 2⋅63 mg/dl) than after GL (135⋅87 (sem 4⋅88) mg/dl; P <0⋅001), TM (127⋅93 (sem 4⋅05) mg/dl; P = 0⋅001), MIX15% (124⋅67 (sem 5⋅73) mg/dl; P = 0⋅039) and MIX50% (129⋅33 (sem 5⋅23) mg/dl; P = 0⋅003) (1 mg/dl = 0⋅0555 mmol/l). In addition, TRM also significantly reduced serum insulin (13⋅01 (sem 2⋅12) μIU/ml) compared with GL (47⋅90 (sem 11⋅93) μIU/ml; P = 0⋅013), TM (52⋅96 (sem 17⋅68) μIU/ml; P = 0⋅002) and MIX50% (33⋅16 (sem 4⋅99) μIU/ml; P = 0⋅008). However, there were no significant differences in subjective appetite between treatments (P > 0⋅05). A single high dose of TRM (50 g) caused flatulence (P < 0⋅05). Tapioca resistant maltodextrin has low digestibility in the small intestine and, therefore, reduced incremental plasma glucose and serum insulin, without affecting satiety in healthy subjects over 180 min. Gastrointestinal tolerability of TRM should be considered when consumed in high doses.

Resistant glucan (RG) and hydrogenated resistant glucan (HRG) are newly developed non-digestible carbohydrate materials that decrease lifestyle-related diseases. The bioavailability of RG and HRG was investigated by in vitro experiments using human and rat small intestinal enzymes and by in vivo experiments using rats in the present study. Oligosaccharides, which are minor components of RG and HRG, were hydrolysed slightly by small intestinal enzymes of humans and rats, and the hydrolysing activity was slightly higher in rats than in humans. The amount of glucose released from HRG was greater than that from RG. However, the high-molecular-weight carbohydrates of the main components were hardly hydrolysed. Furthermore, neither RG nor HRG inhibited disaccharidase activity. When rats were raised on a diet containing 5 % of RG, HRG, resistant maltodextrin or fructo-oligosaccharide (FOS) for 4 weeks, all rats developed loose stools and did not recover during the experiment, except for the FOS group. Body weight gain was normal in all groups and was not significantly different compared with the control group. Caecal tissue and content weights were significantly increased by feeding RG or HRG, although other organ and tissue weights were not significantly different among the groups. In conclusion, RG and HRG consist of small amounts of glucose and digestible and non-digestible oligosaccharides, and large amounts of glucose polymers, which were hardly hydrolysed by α-amylase and small intestinal enzymes. RG and HRG, which were developed newly as dietary fibre materials, had no harmful effects on the growth and development of rats.

Glucagon-like peptide-1 (GLP-1), which is produced and released from enteroendocrine L cells, plays pivotal roles in postprandial glycaemia. The ingestion of resistant maltodextrin (RMD), a water-soluble non-digestible saccharide, improves the glycaemic response. In the present study, we examined whether the continuous feeding of RMD to rats affected GLP-1 levels and glycaemic control. Male Sprague–Dawley rats (6 weeks of age) were fed an American Institute of Nutrition (AIN)-93G-based diet containing either cellulose (5 %) as a control, RMD (2·5 or 5 %), or fructo-oligosaccharides (FOS, 2·5 or 5 %) for 7 weeks. During the test period, an intraperitoneal glucose tolerance test (IPGTT) was performed after 6 weeks. Fasting GLP-1 levels were significantly higher in the 5 % RMD group than in the control group after 6 weeks. The IPGTT results showed that the glycaemic response was lower in the 5 % RMD group than in the control group. Lower caecal pH, higher caecal tissue and content weights were observed in the RMD and FOS groups. Proglucagon mRNA levels were increased in the caecum and colon of both RMD and FOS groups, whereas caecal GLP-1 content was increased in the 5 % RMD group. In addition, a 1 h RMD exposure induced GLP-1 secretion in an enteroendocrine L-cell model, and single oral administration of RMD increased plasma GLP-1 levels in conscious rats. The present study demonstrates that continuous ingestion of RMD increased GLP-1 secretion and production in normal rats, which could be stimulated by its direct and indirect (enhanced gut fermentation) effects on GLP-1-producing cells, and contribute to improving glucose tolerance.