Ingestion of a high-molecular-weight hydrothermally modified waxy maize starch alters metabolic responses to prolonged exercise in trained cyclists.

OBJECTIVE We examined whether the ingestion of a hydrothermally modified starch (HMS) would alter metabolic and hormonal responses to prolonged cycling compared with maltodextrin (MAL). METHODS Nine male cyclists (30 ± 2 y, 79.2 ± 2.1 kg, 4.7 ± 0.1 L of O(2)/min, 7.5 ± 1.3 y training) fasted 10 h before cycling for 150 min at 70% peak oxygen consumption and completing a cycling-to-exhaustion trial at 100% peak oxygen consumption. Participants ingested 1g/kg of HMS or MAL 30 min before and within 10 min of completing the bout. Blood samples were provided every 15 min before, during, and 90 min after exercise. Expired gases were collected every 30 min during exercise. In a crossover, randomized, and double-blind fashion, identical testing was completed 1 wk later. RESULTS Primary findings from this study were that 1) increases in serum glucose were greater during MAL (peak 9.5 mM) versus HMS (peak 7.4 mM, P ≤ 0.01), 2) insulin levels were significantly lower during HMS (peak 2.5 μIU/mL) versus MAL (peak 20.3 μIU/mL, P < 0.001), and 3) HMS was associated with greater fat breakdown as indicated by the increased serum non-esterified fatty acids (P < 0.01) and glycerol levels (P < 0.05). CONCLUSION Ingestion of a low-glycemic HMS before prolonged cycling exercise blunted the initial spike in serum glucose and insulin and increased the breakdown in fat compared with MAL.