Ilex paraguariensis (IP) is a plant rich in polyphenols, saponins and xanthines consumed in beverages by millions of people world-wide, but its metabolic effects remain unknown. Traditionally IP has been considered a stimulant and recent research suggests that it increases fat oxidation during exercise. Our aim was to test the effect of IP on substrate utilisation during submaximal exercise and endurance performance in athletes. Eleven well-trained male cyclists (Age, mean +/- SD 30 +/- 3 y; Weight, 75 +/-7 kg; VO2max 71 +/- 6 ml/kg/min; PPO 403 +/- 32 W) participated in a double-blind counterbalanced crossover study design. Participants ingested 5 g of IP or placebo (PL; maltodextrin) daily for 5 days, and 1 h prior to an experimental trial. Prior to the study, IP samples were characterized phytochemically. Experimental trials were conducted in the morning, with fasted participants, after 48 h of exercise control and 24 h of dietary provision (8 g CHO/kg). Tests included a submaximal step-test (SST) at 30,40,50,60,70 and 80% of VO2max for 5 min per stage, followed by 10 min recovery and an ergometer-based time-trial (TT; n=9) to complete a predetermined amount of mechanical work and last ~30 min. During SST and selected TT time-points, respiratory gases were collected and analysed through an automated gas analysis system. Venous blood samples were taken prior to ingestion of treatment, pre-SST, post-SST and every 1/3 of TT. Plasma was analysed for free fatty acids (FFA), glycerol, glucose and lactate. Results show a small (ES=.38) but significant (p<.05) improvement of IP in time to complete TT from 30.1 +/-1.8 to 29.4 +/-1.4 min, and a concomitant small increase (2.3%) in power output (ES=.2; p<.05). Blood parameters remained unchanged at rest. [FFA] was lower from rest and IP in PL pre-SST (p<.05). [Glycerol] increased above rest at all timepoints after SST in both treatments (p<.05) and in IP vs PL post-SST and at 1/3 TT (p..05). [Lactate] increased above rest at all time-points post-SST (p<.001) and was higher in IP vs PL at 2/3 and 3/3 TT (p<.02). Respiratory gas analyses show lower fat oxidation in PL vs IP at 30, 40, 50 and 60% of VO2max (p..05) but no differences during TT. In conclusion, there was a small but significant increase in performance with IP and markers of fat utilization were lower in PL during SST compared to IP.
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