A Pilot Study to Assess Glucose, Insulin, and Incretin Responses Following Novel High Resistant Starch Rice Ingestion in Healthy Men

Abstract

Introduction: A newly developed resistant starch (RS) rice line with double mutation of starch synthase IIIa and branching enzyme IIb (ss3a/be2b) exhibits a tenfold greater percentage RS value than the wild-type rice line. Currently, the effects of cooked rice with such high RS content on secretion and action of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are unclear. Therefore, we conducted a pilot study to assess postprandial responses of GLP-1 and GIP along with glucose and insulin and also gastric emptying after ingestion of the high-RS cooked rice with ss3a/be2b in healthy subjects.

Methods: In a non-randomized crossover design, five healthy men ingested two test foods, control (low-RS) and high-RS cooked rice, with at least 1-week washout period between testing days. Plasma glucose, serum insulin, plasma total GLP-1, plasma total GIP, and also gastric emptying rate were measured after ingestion of each test food, and the incremental area under the curves (iAUC) was calculated for each biochemical parameter using the values from 0 to 180 min after ingestion.

Results: The high-RS cooked rice ingestion tended to reduce iAUC-glucose (p = 0.06) and significantly reduced iAUC-insulin (p < 0.01) and iAUC-GLP-1 (p < 0.05) but not iAUC-GIP (p = 0.21) relative to control cooked rice ingestion. In addition, the high-RS cooked rice ingestion did not affect gastric emptying.

Conclusions: The present results indicate that the suppressive effects of the high-RS cooked rice ingestion on postprandial responses of glucose and insulin may be provided through attenuation in GLP-1 secretion along with its low digestibility into glucose. We suggest that the high-RS rice with ss3a/be2b may serve as a better carbohydrate source and also as a novel functional food for dietary interventions to improve postprandial hyperglycemia and hyperinsulinemia without both enhancing GLP-1 secretion and affecting gastric emptying in patients with diabetes.

Keywords: Cooked rice; Gastric emptying; Glucagon-like peptide-1; Glucose; Glucose-dependent insulinotropic polypeptide; Insulin; Resistant starch.

Fig. 1

Study protocol of the study

Fig. 2

Changes in plasma glucose and serum insulin levels. A Plasma glucose and B serum insulin levels after ingestion of control and RS cocked rice. C iAUC-glucose and D iAUC-insulin calculated using the values from 0 to 180 min after ingestion of control and RS cocked rice

Fig. 3

Changes in plasma total GLP-1 and GIP levels. A Plasma total GLP-1 and B plasma total GIP levels after ingestion of control and RS cocked rice. C iAUC-GLP-1 and D iAUC-GIP calculated using the values from 0 to 180 min after ingestion of control and RS cocked rice

Fig. 4

Changes in gastric emptying. A Gastric emptying rate, B time_50%, and C gastric emptying coefficient after ingestion of control and RS cocked rice

Fig. 5

Proposed mechanism of attenuation in postprandial responses of glucose, insulin, and GLP-1 after high-RS cooked rice ingestion. High-RS cooked rice is more resistant to digestion into glucose molecule as compared with low-RS cooked rice, and therefore the amount of glucose reaching small intestine is diminished after high-RS cooked rice ingestion. Lowered luminal glucose concentration in the small intestine could lead to reduction in intestinal glucose absorption and subsequent attenuation in glucose-stimulated insulin secretion. Furthermore, since GLP-1-secreting L-cells are located in more distal part of small intestine than GIP-secreting K-cells, the amount of glucose reaching there would be markedly decreased after high-RS cooked rice ingestion, consequently leading to attenuation in nutrient (glucose)-stimulated GLP-1 release and further suppression of insulin secretion through GLP-1 receptor signaling