Effects of Low Versus Moderate Glycemic Index Diets on Aerobic Capacity in Endurance Runners: Three-Week Randomized Controlled Crossover Trial.

Krzysztof Durkalec-Michalski,Bogna Zawieja,Dominika Jurkowska,Jan Jeszka,Emilia Zawieja,Maciej Buchowski

doi:10.3390/nu10030370

Krzysztof Durkalec-Michalski, Bogna Zawieja + Show 4 more

Open Access

https://doi.org/10.3390/nu10030370

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Abstract

The glycemic index (GI) of ingested carbohydrates may influence substrate oxidation during exercise and athletic performance. Therefore, the aim of this study was to assess the effect of low- and moderate-GI three-week diets on aerobic capacity and endurance performance in runners. We conducted a randomized crossover feeding study of matched diets differing only in GI (low vs. moderate) in 21 endurance-trained runners. Each participant consumed both, low- (LGI) and moderate-GI (MGI) high-carbohydrate (~60%) and nutrient-balanced diets for three weeks each. At the beginning and end of each diet, participants had their aerobic capacity and body composition measured and performed a 12-min running test. After LGI, time to exhaustion during incremental cycling test (ICT) and distance covered in the 12-min run were significantly increased. The MGI diet led to an increase in maximal oxygen uptake (O2max), but no performance benefits were found after the MGI diet. The LGI and MGI diets improved time and workload at gas exchange threshold (GET) during ICT. The results indicate that a three-week high-carbohydrate LGI diet resulted in a small but significant improvement in athletic performance in endurance runners. Observed increase in O2max on MGI diet did not affect performance.

Highlights

Carbohydrates and fat are the main sources of fuel oxidized in muscles during endurance exercise [1]
The glycemic index (GI) of a food is defined as the incremental area under the two-hour blood glucose response curve (AUC) following consumption of the tested food usually containing 50 g of CHO and divided by the AUC of a reference food containing the same amount of CHO and multiplied by 100
The major findings are that the LGI diet consumed for three three weeks by actively training endurance runners may improve distance covered in the 12‐min weeks by actively training endurance runners may improve distance covered in the 12-min running running test and time to exhaustion in incremental cycling test (ICT)

Summary

Introduction

Carbohydrates and fat are the main sources of fuel oxidized in muscles during endurance exercise [1]. Exercise-induced hypoglycemia contributes to the perception of fatigue and attenuates athletic performance [2]. While the ingestion of adequate amounts of carbohydrates is vital to maintain glucose availability and optimize athletic performance [1], the carbohydrate quality may play an important role because various carbohydrate-rich foods affect postprandial glycaemia differently. The glycemic index (GI) classifies carbohydrate-containing foods based on their postprandial glycemic response [3]. The GI of a food is defined as the incremental area under the two-hour blood glucose response curve (AUC) following consumption of the tested food usually containing 50 g of CHO and divided by the AUC of a reference food containing the same amount of CHO (either glucose or white bread) and multiplied by 100. Foods with a high GI increase blood glucose

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