Glycaemic index of parboiled rice depends on the severity of processing: study in type 2 diabetic subjects

Objective: To study the influence of parboiling and the severity of the process on glycaemic and insulinaemic responses to rice in type 2 diabetes. Moreover, to examine changes in starch structure related to parboiling, which may affect the metabolic responses and digestibility. Design: Nine type 2 diabetic subjects ingested four test meals: white bread (WB) and three meals of cooked polished rice of the same variety being non-parboiled (NP), mildly traditionally parboiled (TP) and severely pressure parboiled (PP). The participants ingested the test meals (50 g available carbohydrates) on separate occasions after an overnight fast. Setting: Outpatient clinic, Dept. Endocrinology and Metabolism, Aarhus University Hospital, Denmark. Results: All three rice samples elicited lower postprandial plasma glucose response (NP: 335 +/- 43; TP: 274 +/- 53; PP: 231 +/- 37 mmol/ 1*180 min.; means +/- s.e.m.) than white bread (626 +/- 80; P < 0.001), within rice samples PP tended to be lower than NP (P = 0.07). The glycaemic indices were: NP: 55 +/- 5, TP: 46 +/- 8 and PP: 39 +/- 6, and lower for PP than NP (P < 0.05). The insulin responses were similar for the three rice meals, which were all lower than that to white bread (P < 0.001). Differential scanning calorimetry showed the presence of amylose-lipid complexes in all rice samples and of retrograded amylopectin in PP. Amylose retrogradation was not detected in any of the rice samples. Conclusions: All rice test meals were low-glycaemic in type 2 diabetic subjects. There was no effect of TP on glycaemic index, whereas PP reduced the glycaemic index by almost 30% compared to NP.