Scientific Study

PURPOSE: To compare serum glucose and insulin responses to 3 preexercise snacks before; during; and after exercise in individuals with impaired fasting glucose (IFG) and healthy (H) men. In addition; in an IFG population; the authors sought to determine whether a natural fruit snack (i.e.; raisins) yields more desirable glucose and insulin concentrations than an energy bar or a glucose solution. METHODS: The IFG (n = 11; age = 54.5 ± 1.3 yr; fasting blood glucose [BG] = 6.3 ± 0.1 mmol/L) and H groups (n = 9; age = 48.0 ± 3.1 yr; fasting BG = 4.9 ± 0.1 mmol/L) cycled at 50% of VO2peak for 45 min on 4 occasions after consuming water or 50 g of carbohydrate from raisins (R); an energy bar (EB); or a glucose beverage (GLU). Metabolic markers were measured before; during; and after exercise. RESULTS: In all nutritional conditions; glucose concentrations of the IFG group were consistently higher than in the H group. Differences between IFG and H groups in insulin concentrations were sporadic and isolated. In the IFG group; preexercise glucose concentration was lower in the R condition than in GLU. Ten and 20 min into exercise; glucose concentrations in the R and EB conditions were lower than in GLU. Insulin concentrations were lower in the R condition than in EB and GLU immediately before exercise and at Minute 10 but at 20 min R remained lower than only GLU. CONCLUSION: Glucose concentrations were higher in the IFG group regardless of preexercise snack. Compared with the glucose solution; raisins lowered both the postprandial glycemic and insulinemic responses; whereas the energy bar reduced glycemia but not insulinemia.