Determination of the glycemic and insulinemic indexes of raisins in three populations

Abstract

There are only limited published data on the glycemic index (GI) and insulin index (II) of raisins. Further, the GI and II 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 II 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=21.7±1.7 kg/m2), 11 endurance athletes (A, 23.1±1.0 y, BMI=24.1±0.4 kg/m2), and 11 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±4.7) 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 II values of raisins were 47.3±9.4, 51.9±6.5, and 54.4±9.3 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<0.05). In summary, raisins are a low to moderate GI food and their II is proportionate to their GI, regardless of the population studied. Athletes were able to normalize postprandial glycemia with lower insulin secretion. Funded by the California Raisin Marketing Board