Effect Of Glycemic Index Meal And Carbohydrate Solution On Immune Responses And Running Performance

Abstract

Increasing evidence suggested that physical stress to immune system can be reduced by ingestion of carbohydrate (CHO) before and during prolonged exercise. However, little research has been undertaken to investigate the role of glycemic index (GI) on immune function and exercise performance. PURPOSE To investigate the effect of pre-exercise GI meal on the immune responses and endurance running performance. METHODS Eight endurance-trained male runners (Age: 28.6 ±2.7ys; Body mass: 61.9±1.71 kg; VO2max:58.5±1.6ml.kg−1min−1) completed three trials in a randomized order, separated by at least 7 days. Pre-exercise meal consisted of either high GI meal (GI=83, HGI), lower GI meal (GI=36, LGI) or control (CON) (low energy sugar-free jelly) was given to the subjects 2 hours before the performance run on a level treadmill, i.e., 5-km of run at 70% VO max followed by a 16-km self-paced run. The two GI meals were isocalaric (61.2% CHO; 14.1% protein; 24.7% fat) and provided 1.5 g CHO.kg−1 BM. During each trial, 2ml.kg−1BM of 6.6% CHO-electrolyte solution was consumed immediate pre-exercise and every 2.5-km afterward. Venous blood samples were collected before the meals (PRE-2h), immediately before the exercise (PRE-ex), 15min (POST-0.25h) and 60min after exercise (POST-1h) respectively and were assayed for plasma cytokines, cortisol, glucose and insulin. RESULTS There was no difference in time to complete the 21-km run between LGI and HGI (92.4 ± 6.7minvs 91.5 ± 6.3min, NS) but difference was observed between the HGI and CON (91.5 ± 6.3min vs 93.6 ± 6.0min, P<0.05). No overshooting response of tumour necrosis factor alpha (TNF-D) after exercise was detected in all trials. The concentration of interleukin 6 (IL-6) increased by more than 100 times at POST-0.25h in all trials and returned to the PRE-ex level on LGI but not on CON (P<0.05) and HGI (P<0.01). In contrast, the interleukin 2 (IL-2) concentrations decreased at POST-0.25h on CON only (P<0.001) and returned to baseline level by POST-1h in all trials. The blood glucose concentrations in HGI did not return to the pre-diet level by the POST-1h when compared with CON and LGI. Cortisol levels increased during the post exercise period and were lower on LGI but not on HGI when compared to CON (P<0.05) at the POST-1h. CONCLUSIONS The results suggested that running performance was improved when CHO-electrolyte solution was consumed during the run after the pre-exercise HGI meal when compared with CON. However, pre-exercise LGI meal attenuated the increases in cortisol and hastened the recovery of the increased IL-6 to normal value when compared with HGI and CON at POST-1h.