The Effect of Carbohydrate Gels on Gastrointestinal Tolerance During a 16-km Run

Two studies were conducted to investigate gastrointestinal (GI) tolerance of high carbohydrate (CHO) intakes during intense running. The first study investigated tolerance of a CHO gel delivering glucose plus fructose (GLU+FRC) at different rates. The second study investigated tolerance of high intakes of glucose (GLU) vs. GLU+FRC gel. Both studies used a randomized, 2-treatment, 2-period crossover design: Endurance-trained men and women (Study 1: 26 men, 8 women; 37 +/- 11 yr; 73 9 kg; 1.76 +/- 0.07 m. Study 2: 34 men, 14 women 35 +/- 10 yr: 70 +/- 9 kg; 1.75 +/- 0.09 m) completed two 16-km outdoor-runs. In Study 1 gels were administered to provide 1.0 or 1.4 g CHO/min with ad libitum water intake every 3.2 km. In Study 2 GLU or GLU+FRC gels were given in a double-blind manner to provide 1.4 g CHO/min. In both studies a postexercise questionnaire assessed 17 symptoms on a 10-point scale (from 0 to 9). For all treatments, G1 complaints were mainly scored at the low end of the scale. In Study I mean scores ranged from 0.00 +/- 0.00 to 1.12 +/- 1.90, and in Study 2, from 0.00 +/- 0.0 to 1.27 +/- 1.78. GI symptoms were grouped into upper abdominal, lower abdominal, and systemic problems. There were no significant treatment differences in these categories in either study. In conclusion, despite high CHO-gel intake, and regardless of the blend (GLU vs. GLU+FRC), average scores for GI symptoms were at the low end of the scale, indicating predominantly good tolerance during a 16-km run. Nevertheless, some runners (similar to 10-20%) experienced serious problems, and individualized feeding strategies might be required.