Dietary approach to modulate postprandial glucose absorption, gastric emptying, and long-term food intake using starch-entrapped microspheres

Consumption of low-glycemic index (GI) foods has been associated with desirable health benefits such as reduced risk for obesity, diabetes, and cardiovascular diseases. The physiological responses to slowly digestible starch (SDS) have been deduced from low-GI foods due to their similar glycemic responses. However, there is not yet been a study where a SDS material with rate of digestion and locational glucose deposition in the small intestine is manipulable so that the physiological effects of SDS can be studied in a systematic and controlled way. Alginate-entrapped starch microspheres with different slow digesting rates were previously designed and researched in our laboratory. In this thesis study, the physiological effects were investigated in vivo of microspheres that release glucose slowly and throughout the small intestine compared to rapidly digestible starch (RDS) that releases glucose rapidly in the proximal small intestine with the aim to: 1) evaluate the relationship between changes in the activity of the α-glucosidases (the mucosal starch digestive enzymes that consist of sucrase-isomaltase and maltase-glucoamylase) responding to SDS and the postprandial glucose absorption from a digestible starch feed; 2) investigate the effect of glucose deposition particularly into the ileum through SDS on gastric emptying via a dietary approach on the ileal brake mechanism affecting rate of gastric emptying; and 3) examine the effect of long-term feeding of SDS on food intake behavior. The results showed that decreased starch substrate availability in the jejunum from feeding SDS for 1 week reduced jejunal α-glucosidase activities and subsequently decreased glucose absorption from an acute digestible starch feed. Acute feeding of SDS with different digestion rates slowed gastric emptying in rats in a dose-dependent manner, which was likely attributed to the hormonal and/or neural mechanisms that the distally released glucose triggers. Lastly, long-term feeding of SDS in diet-induced obese rats for 11 weeks reduced daily intake to the same level as in the low-fat (LF) lean control group, compared to the RDS diet-induced obese group. SDS led to substantially lower meal size compared to the lean control and RDS groups; and initially higher meal frequency that decreased to the same level as in other treatment groups towards the end of the study. Suppressed hypothalamic orexigenic neuropeptide Y (NPY) and agouti-related peptide (AgRP) gene expression in the SDS group compared to the RDS group supported a mechanistic basis for the observed change in feeding behavior induced by SDS. The findings of our study show desirable physiological effects of slowly digestible starch with locational (ileal) glucose deposition, and thus demonstrate the potential of a practical and beneficial application of a dietary approach in postprandial glucose control. Implications include maintenance of glucose homeostasis, appetite and food intake control, as well as in weight management in overweight populations