Two weeks of repetitive gut-challenge reduce exercise-associated gastrointestinal symptoms and malabsorption

Scand J Med Sci Sports. 2018 Feb;28(2):630-640. doi: 10.1111/sms.12912. Epub 2017 Jun 19.


Debilitating gastrointestinal symptoms is a common feature of endurance running and may be exacerbated by and/or limit the ability to tolerate carbohydrate intake during exercise. The study aimed to determine whether two weeks of repetitive gut-challenge during running can reduce exercise-associated gastrointestinal symptoms and carbohydrate malabsorption. Endurance runners (n=18) performed an initial gut-challenge trial (GC1) comprising 2-hour running exercise at 60% VO2max (steady state) while consuming a formulated gel-disk containing 30 g carbohydrates (2:1 glucose-fructose, 10% w/v) every 20 minutes, followed by a 1-hour running effort bout. Gastrointestinal symptoms, feeding tolerance, and breath hydrogen (H2 ) were determined along the gut-challenge trial. After GC1, participants were randomly assigned to a blinded carbohydrate (CHO, 90 gCHO hour-1 ) or placebo (PLA, 0 gCHO hour-1 ) gut-training group. This comprised of consuming the group-specific feeding intervention during 1-hour running exercise at 60% VO2max equivalent, daily over a period of two weeks. Participants then repeated the gut-challenge trial (GC2). In GC2, a reduced gut discomfort (P=.012), total (P=.009), upper- (P=.015), and lower-gastrointestinal (P=.008) symptoms, and nausea (P=.05) were observed on CHO, but not PLA. Feeding tolerance did not differ between GC1 and GC2 on CHO and PLA. H2 peak was attenuated in GC2 (6±3 ppm) compared to GC1 (13±6 ppm) on CHO (P=.004), but not on PLA (GC1 11±7 ppm, and GC2 10±10 ppm). The effort bout distance was greater in GC2 (12.3±1.3 km) compared with GC1 (11.7±1.5 km) on CHO (P=.035) only. Two weeks of repetitive gut-challenge improve gastrointestinal symptoms and reduce carbohydrate malabsorption during endurance running, which may have performance implications.

Keywords: breath hydrogen; discomfort; endurance; fructose; glucose; gut training; running.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Carbohydrate Metabolism
  • Dietary Carbohydrates / administration & dosage*
  • Female
  • Fructose / administration & dosage
  • Gastrointestinal Diseases / prevention & control*
  • Gastrointestinal Tract / physiopathology*
  • Glucose / administration & dosage
  • Humans
  • Male
  • Oxygen Consumption
  • Running*


  • Dietary Carbohydrates
  • Fructose
  • Glucose