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Reducing the Risk for GI Problems during High-Intensity Endurance Training

By: NCSF  on:  Mar 18 2014
1  Commentscomments

Clients who regularly compete in events from 5Ks to marathons and beyond will agree that steps must be taken to reduce the risk for gastrointestinal (GI) tract problems during both races and training sessions. It is well-known that long-duration endurance training can directly damage the GI tract and cause debilitating symptoms, especially when combined with inappropriate nutritional intake. Research indicates the 30-50% of endurance athletes experience some sort of GI issues related to their training. This value may be higher among recreational competitors who lack the training, nutritional expertise and guidance elite athletes often possess. Interestingly, GI issues appear to occur more frequently among women and individuals who run as opposed to those who cycle or swim. The latter may be directly due to the repeated jostling effect placed upon digestive tissues from the high-impact nature of running.

Frequently reported GI problems resulting from intense endurance training:

  • Upper GI
    • Heartburn, bloating, nausea, vomiting
  • Lower GI
    • Urge to defecate or urinate, loose stool or diarrhea, intestinal bleeding
  • Related issues
    • Nausea, dizziness, side ache (stitch)

There are many potential causes for the above issues which can stem from physiological, mechanical or nutritional factors. High anxiety or stress often associated with competition can significantly reduce blood flow to the GI tract. This promotes hypoxia and increases the risk for direct damage to the colon. As it relates to mechanical causative factors, (1) the high-impact forces of repeated foot contacts during running have been shown to potentially cause intestinal bleeding and blood in the feces; (2) continuous jostling of the trunk and pelvis is thought to contribute to flatulence, diarrhea, and an urgency to defecate; (3) postural modifications such as leaning forward during cycling (or due to fatigue) can increase compressive forces upon the abdomen and GI tract; and (4) “swallowing” of air can cause moderate stomach distress. Nutritional causes of GI-related problems on the other hand are more controllable by the exercise participant. Potential causes include the ingestion of fiber, fat, protein or fructose during or immediately prior to training, dehydration, ingestion of fluid with a high osmolarity during training (e.g., fruit juice), and ingestion of dairy products before or during training/competition. In addition, it has been shown that consumption of allergenic foods such as wheat, eggs, chicken, shrimp, shellfish, nuts, fruits, and vegetables, followed by exercise may induce food-dependent exercise-induced anaphylaxis (FDEIAn). FDEIAn is separate from food allergies and is more likely triggered by high intensity and frequent exercise.

While also considering the above causes and risk factors, competitive or recreational endurance athletes should make note of the following research-based recommendations for preventing GI problems. Unfortunately, strict and precise guidelines are limited due to the fact that each individual’s physiology has an impact on how stress affects their digestive system as well as other factors.

Recommendations purported to reduce the risk for GI problems during high-intensity endurance training:

  • Avoid milk products before exercise or a race
    • Even mild intolerance can cause problems
  • Avoid high-fiber foods prior to competition
    • Can cause unwanted bowel movement and GI discomfort
  • Practice stress management methods prior to a big race
  • Avoid aspirin and NSAIDs
    • Seem to increase the incidence of GI complaints
  • Avoid high-fructose foods and drinks before competition
    • Not rapidly absorbed and known to be less tolerated than high-glucose selections
    • Remember that high-osmolarity beverages limit stomach (gastric) emptying, which promotes discomfort as well as a lower rate of fluid absorption
  • Time pre-competition meals appropriately
    • A high-carbohydrate, low protein meal 3-5 hours before a race containing 400-500 kcals may be optimal
    • Another small meal may be consumed about an hour before a race containing well-tolerated, easily-digestible carbohydrates (white rice)
  • Consume appropriate carbohydrate/food sources during prolonged training (sport drinks, gels, and other easily-digestible options) at a rate of about 60-70 g/hr
  • Practice new nutrition strategies for use prior to exercise or competition, and stick with what works best
    • Individual-specific factors (hormonal and digestive) make personalized strategies a must
Matthew Potts
Date: Mar 24 2014 9:44 AM
I'd recommend steering clear of metabolism-boosting foods prior to any endurance exercising. Foods with heat naturally stimulate the metabolism and therefore present GI problems once the exercising has started. Hi-fat foods pose problems to well-trained, low-fat practicing individuals. Diarrhea is the main symptom. Matt's Personal Training Minersville, PA
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