Carbohydrate Intake Does Not Counter the Post-Exercise Decrease in Natural Killer Cell Cytotoxicity

In a study using a randomized crossover approach, cyclists (n = 20, overnight fasted) engaged in three 75 km time trials while ingesting water (WAT) or carbohydrate (0.2 g/kg every 15 min) from bananas (BAN) or a 6% sugar beverage (SUG). Blood samples were collected pre-exercise and 0 h, 1.5 h, and 21 h post-exercise and analyzed for natural killer (NK) cytotoxicity activity (NKCA) using pure NK cell populations. The two carbohydrate trials (BAN, SUG) compared to WAT were associated with higher post-exercise glucose and lower cortisol, total blood leukocyte, neutrophil, and NK cell counts (interaction effects, p < 0.001). The immediate post-exercise increase in NK cell counts was higher in WAT (78%) compared to BAN (32%) and SUG (15%) trials (p ≤ 0.017). The 1.5 h post-exercise decrease in NK cell counts did not differ after WAT (-46%), BAN (-46%), and SUG (-51%) trials. The pattern of change in post-exercise NKCA differed between trials (p < 0.001). The 1.5 h post-exercise decreases in NKCA were 23%, 29%, and 33% in the WAT, BAN, and SUG trials, respectively, but trial contrasts did not differ significantly. Carbohydrate ingestion from BAN or SUG attenuated immediate post-exercise increases in leukocyte, neutrophil, and NK cell counts, but did not counter the 1.5 h decreases in NK cell counts and NKCA.