Pre-exercise ingestion of a low glycaemic index rice-based mixed meal increases fat oxidation and endurance running performance in a hot-humid environment

Relative to exercise in a thermoneutral environment, there is only limited evidence demonstrating that a low glycaemic index (LGI) pre-exercise meal can enhance endurance exercise performance in a hot-humid (HH) condition. Also, previous studies predominantly utilised Western-based and single food items, with minimal focus on Asian-based mixed meals. This study aimed to investigate the impact of pre-exercise LGI and high glycaemic index (HGI) rice-based mixed meals on endurance performance among acclimatised trained athletes in HH condition (32 °C, 65% relative humidity). Twelve native-born endurance-trained male runners (age 22.0 ± 5.8 years; peak oxygen consumption (V̇O_2peak) 64.2 ± 5.5 mL kg^-1 min^-1) completed two trials consisting of 45 min steady-state (SS) run at 70% V̇O_2peak followed by 10 km performance run (TT_10km). Three hours before exercise, participants consumed an isocaloric rice-based mixed meals containing either LGI (GI value = 47) or HGI (GI value = 80), providing 1.3 g of carbohydrate (CHO) per kg of body mass. Participants ran faster during TT_{10 km} after consuming the LGI meal compared to the HGI meal (LGI: 55.18 ± 1.22 vs. HGI: 57.03 ± 2.25 min, <i>p</i> = 0.010). End rectal temperature did not significantly differ between trials (LGI: 39.16 ± 0.74 vs. HGI: 38.95 ± 0.46 °C, <i>p</i> = 0.352). Fat oxidation was higher during the SS run in the LGI compared to the HGI trial (LGI: 0.19 ± 0.05 vs. HGI: 0.13 ± 0.19 g min^-1, <i>p</i> = 0.001). This study demonstrated that, relative to HGI, consuming a pre-exercise LGI rice-based mixed meal enhanced endurance performance in HH environment among acclimatised trained male athletes.