ABSTRACT Nine ultra‐endurance athletes completed a randomised, crossover trial involving two 28‐day dietary arms during which the athletes consumed a carbohydrate‐rich diet (carbohydrate 58 ± 3, protein 15 ± 2 and fat 26 ± 2%) containing low‐ or high‐glycaemic‐index (LGI or HGI, respectively) carbohydrates. At the start and end of each dietary arm, participants performed a fasted 3‐h submaximal run outdoors before ingesting either a low (GI = 32, isomaltulose Palatinose) or high (GI = 100, maltodextrin) glycaemic index drink (0.75 g/kg bm/h over 3.5 h). Participants then completed a treadmill run to exhaustion at 74 ± 1% vO 2peak , with pulmonary gas exchange measured over the first hour. Interstitial glucose iG was measured via continuous glucose monitoring (Supersapiens, Atlanta, USA). Data were analysed ANOVA and post hoc t ‐tests with Bonferroni adjustment as appropriate, with p ≤ 0.05 accepted as significant. Mean 24‐h iG was similar between diets (LGI:102 ± 5 vs. HGI:100 ± 5 mg/dL). iG variability measures, including standard deviation (LGI:17 ± 1 vs. HGI:18 ± 2 mg/dL, p = 0.016) and coefficient of variation (LGI:16 ± 1% vs. HGI:18 ± 1%, p = 0.0003), were lower in the LGI diet, with a reduced percentage of time spent below the recommended range (LGI 2 ± 1% vs. HGI 4 ± 2%, p = 0.006. Level 1 55–69 mg/dL LGI 1 ± 1% vs. HGI 3 ± 2, p = 0.005). Carbohydrate oxidation during the first hour of the run test was reduced in the LGI diet arm (ΔLGI −0.14 ± 0.32 vs. ΔHGI 0.06 ± 0.28 g·min −1 , p = 0.016) but endurance capacity was similar across diets. Adopting a 28‐day LGI carbohydrate‐rich diet and incorporating isomaltulose improved glycaemic variability and reduced time spent below the target glycaemic range with evidence of similar endurance performance capability when compared to a HGI carbohydrate‐rich diet.
Hamilton et al. (Tue,) studied this question.
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