Low glycemic-index foods may reduce postprandial oxidative stress by reducing postprandial glucose excursions, but the evidence for this is limited by dietary confounders. To determine whether reducing postprandial glucose per se reduces postprandial oxidative stress, overnight-fasted participants (BMI 25.0–39.9 kg/m², n = 18) consumed four test meals in random order: 75 g dextrose solution (Dex) within 5 min (bolus/noC), Dex slowly over 3.25 h (sipping/noC), bolus with 1 g vitamin C (bolus/C) and sipping with 1 g vitamin C (sipping/C). Venous blood was taken at intervals over 6 h; a standard lunch was consumed at 4 h. Sipping flattened postprandial glucose and insulin and reduced free fatty acid rebound compared to bolus (p < 0.05). Vitamin C raised serum vitamin C from ~20 to ~55 μmol/L. The total peroxyl radical trapping antioxidant potential (TRAP) increments differed after lunch, with a main effect of vitamin C at 5 h (mean ± SEM; C 70 ± 23 vs. noC −29 ± 27; p = 0.016) and main effects of rate (sipping 57 ± 25 vs. bolus −71 ± 28; p = 0.0002) and vitamin C (C 58 ± 25 vs. noC −73 ± 28; p = 0.0003) at 6 h. By multiple regression analysis, the TRAP area under the curve (AUC) was positively associated with the insulin AUC (p < 0.001) and negatively with the glucose and vitamin C AUCs (p < 0.05). The oxidized LDL increments were higher 6 h after sipping than bolus (7 ± 7 vs. −20 ± 7, p = 0.005). The oxidized LDL AUC was negatively associated with the TRAP AUC (p < 0.001). These results support the hypothesis that reducing postprandial glucose reduces postprandial oxidative stress.

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