We examined whether ingestion of a modified waxy maize starch (WMS) designed to have a low glycemic impact would alter metabolic and hormonal responses to prolonged cycling compared to Maltodextrin. Ten male cyclists (n: 9, age: 30 2 y, weight: 79.2 2.1 kg, VO2peak: 4.7 0.1 L/min, training: 7.5 1.3 y) fasted for 12 h before cycling for 150 min @ 70% VO2peak. Before and after exercise, participants ingested 1g/kg of either WMS or Maltodextrin while providing blood and expired gas samples every 15 and 30 min, respectively, before, during, and following exercise. In a crossover fashion, identical testing was completed one week later. There was a rapid increase in blood glucose immediately after the ingestion of Maltodextrin pre‐ and post‐exercise, which was significantly attenuated by WMS (P < 0.05). In a similar manner, serum insulin levels were also significantly lower after ingestion of WMS (peak = 2.5 ìIU/ml) compared to Maltodextrin (peak = 20.3 ìIU/ml). WMS was associated with greater fat breakdown and oxidation during exercise and recovery as indicated by significantly increased serum non‐esterified fatty acids and glycerol levels and a trend for lower respiratory exchange ratios compared to Maltodextrin. Ingestion of a low glycemic modified waxy maize starch prior to prolonged submaximal cycling blunted the initial spike in blood glucose and insulin while enhancing breakdown and oxidation of fat.
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