Cooking and processing of food may account for differences in blood glucose and insulin responses to food with similar contents of carbohydrate, fat, and protein. The present study was carried out to see if short-term cooking of rolled oats caused an increase in blood glucose. Furthermore, we wanted to see if dried fruit could substitute for some of the starch without deterioration of the postprandial blood glucose response. We therefore compared the blood glucose and insulin responses to three isocaloric, carbohydrate equivalent meals in 11 normal subjects and 9 Type 2 diabetic patients. Meals composed either of raw rolled oats, oatmeal porridge or a mixture of raw rolled oats with raisins were served. In normal subjects, the three meals produced similar glucose (75 +/- 22, 51 +/- 16 and 71 +/- 23 (+/- SE) mmol l-1 180 min, respectively) and insulin response curves (3160 +/- 507, 2985 +/- 632 and 2775 +/- 398 mU l-1 180 min, respectively). Type 2 diabetic patients also showed similar postprandial blood glucose (515 +/- 95, 531 +/- 83 and 409 +/- 46 mmol l-1 180 min, respectively) and insulin (5121 +/- 850, 6434 +/- 927 and 6021 +/- 974 mU l-1 180 min, respectively) responses to the three meals. Thus short-term cooking of rolled oats has no deleterious effect on blood glucose and insulin responses, and substitution of 25% of the starch meal with simple sugars (raisins) did not affect the blood glucose or insulin responses.