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There are only limited published data on the glycemic index (GI) and insulin index of raisins. Further, the GI and insulin index of raisins have not been determined in endurance athletes or in persons with prediabetes. The objective of this study was to determine both the GI and the insulin index of raisins, and to evaluate if these indexes are similar when measured in different populations. The study groups consisted of 10 healthy sedentary subjects (S, 25.7±1.3 y, BMI=23.3±1.7 kg/m2), 11 endurance athletes (A, 23.1±1.0 y, BMI=24.1±0.3 kg/m2), and 10 prediabetic individuals (P, 50±2.6 y, BMI=32.6±1.9 kg/m2). Subjects consumed 50 g of available carbohydrates from raisins and from a glucose solution (reference food) on two separate occasions. Serum glucose and insulin concentrations were measured from capillary finger-stick blood samples at baseline and at 15, 30, 45, 60, 90, and 120 min (& 150 and 180 min for P) postprandially. The GI of raisins was low (GI≤55) in the S (49.4±7.4) and P (49.6±4.8) groups and was moderate (GI 55-69) in the A group (62.3±10.5), but there were no differences among the groups (P=0.437). The insulin index values of raisins were 47.3±9.4, 51.9±6.5, and 54.4±8.9 for the S, A, and P groups, respectively. On average, the A group secreted 2-2.5-fold less insulin per gram of carbohydrate compared with the S and P groups, respectively (P