Decreasing the RAG:SAG ratio of granola cereal predictably reduces postprandial glucose and insulin responses: a report of four randomised trials in healthy adults.

ABSTRACT

Dietary starch contains rapidly (RAG) and slowly available glucose (SAG). To establish the relationships between the RAGSAG ratio and postprandial glucose, insulin and hunger, we measured postprandial responses elicited by test meals varying in the RAGSAG ratio in n 160 healthy adults, each of whom participated in one of four randomised cross-over studies (n 40 each) a pilot trial comparing six chews (RAGSAG ratio 2·4-42·7) and three studies comparing a test granola (TG1-3, RAGSAG ratio 4·5-5·2) with a control granola (CG1-3, RAGSAG ratio 54·8-69·3). Within studies, test meals were matched for fat, protein and available carbohydrate. Blood glucose, serum insulin and subjective hunger were measured for 3 h. Data were subjected to repeated-measures analysis of variance (ANOVA). The relationships between the RAGSAG ratio and postprandial end points were determined by regression analysis. In the pilot trial, 0-2 h glucose incremental areas under the curve (iAUC0-2; primary end point) varied across the six chews (P = 0·014) with each 50 % reduction in the RAGSAG ratio reducing relative glucose response by 4·0 %. TGs1-3 elicited significantly lower glucose iAUC0-2 than CGs1-3 by 17, 18 and 17 %, respectively (similar to the 15 % reduction predicted by the pilot trial). The combined means ± sem (n 120) for TC and CG were glucose iAUC0-2, 98 ± 4 v. 118 ± 4 mmol × min/l (P < 0·001), and insulin iAUC0-2, 153 ± 9 v. 184 ± 11 nmol × h/l (P < 0·001), respectively. Neither postprandial hunger nor glucose or hunger increments 2 h after eating differed significantly between TG and CG. We concluded that TGs with RAGSAG ratios <5·5 predictably reduced glycaemic and insulinaemic responses compared with CGs with RAGSAG ratios >54. However, compared with CG, TG did not reduce postprandial hunger or delay the return of glucose or hunger to baseline.