Objective and methods: This randomized, double-blind, placebo-controlled study was designed to determine the influence of exercise mode and 6% carbohydrate (C) versus placebo (P) beverage ingestion, on blood cell counts, plasma glucose, hormone, and inflammatory cytokine responses (five total samples over 9 h) to 2.5 h of high-intensity running and cycling (approximately 75% VO2max) by 10 triathletes who acted as their own controls. Statistical significance was set at P < or = 0.05.
Results: C relative to P ingestion (but not exercise mode) was associated with higher plasma levels of glucose and insulin, lower plasma cortisol and growth hormone, and diminished perturbation in blood immune cell counts. The pattern of change over time for interleukin (IL)-6 was significantly different between C and P conditions (P = 0.021) and between running and cycling modes (P < 0.001), with the lowest postexercise values seen in the C-cycling sessions (10.7 +/- 1.8 pg x mL(-1)) and the highest in the P-running sessions (51.6 +/- 14.2 pg x mL(-1)). The pattern of change over time between C and P conditions (but not modes) was significantly different for IL-1 receptor antagonist (P = 0.003), with values once again lowest for the C-cycling sessions (1.5 h postexercise, 301 +/- 114 pg x mL(-1)) and highest for the P-running sessions (1171 +/- 439 pg x mL(-1)).
Conclusion: These data indicate that carbohydrate versus placebo ingestion (4 mL x kg(-1) carbohydrate or placebo every 15 min of the 2.5-h exercise bout) is associated with higher plasma glucose levels, an attenuated cortisol response, and a diminished pro- and anti-inflammatory cytokine response.