Metabolism and performance during extended high-intensity intermittent exercise after consumption of low-and high-glycaemic index pre-exercise meals

Abstract

The metabolic and performance benefits of prior consumption of low-glycaemic index (GI) meals v. high-GI meals were determined in extended high-intensity intermittent exercise. Participants (ten males and four females, aged 25•8 (sd 7•3) years) completed two testing days (each consisting of back-to-back 90-min intermittent high-intensity treadmill running protocols separated by 3 h) spaced by at least 7 d. Using a randomised counterbalanced cross-over design, low-GI, lentil-based meals (GI about 42) or high-GI, potato-based meals (GI about 78) matched for energy value were consumed 2 h before, and within 1 h after, the first exercise session. Performance was measured by the distance covered during five 1-min sprints (separated by 2•5 min walking) at the end of each exercise session. Peak postprandial blood glucose was higher by 30•8 % in the high-GI trial compared with the low-GI trial, as was insulin (P = 0•039 and P = 0•003, respectively). Carbohydrate oxidation was lower by 5•5 % during the low-GI trials compared with the high-GI trials at the start of the first exercise session (P < 0•05). Blood lactate was significantly higher (6•1 v. 2•6 mmol/l; P = 0•019) and blood glucose significantly lower (4•8 v. 5•4 mmol/l; P = 0•039) at the end of the second exercise session during the high-GI trial compared with the low-GI trial. Sprint distance was not significantly different between conditions. A low-GI meal improved the metabolic profile before and during extended high-intensity intermittent exercise, but did not affect performance. Improvements in metabolic responses when consuming low-GI meals before exercise may be beneficial to the long-term health of athletes. © 2012 The Authors.