Assessment of Exercise-Associated Gastrointestinal Perturbations in Research and Practical Settings: Methodological Concerns and Recommendations for Best Practice

Abstract

Strenuous exercise is synonymous with disturbing gastrointestinal integrity and function, subsequently prompting systemic immune responses and exercise-associated gastrointestinal symptoms, a condition established as “exercise-induced gastrointestinal syndrome.” When exercise stress and aligned exacerbation factors (i.e., extrinsic and intrinsic) are of substantial magnitude, these exercise-associated gastrointestinal perturbations can cause performance decrements and health implications of clinical significance. This potentially explains the exponential growth in exploratory, mechanistic, and interventional research in exercise gastroenterology to understand, accurately measure and interpret, and prevent or attenuate the performance debilitating and health consequences of exercise-induced gastrointestinal syndrome. Considering the recent advancement in exercise gastroenterology research, it has been highlighted that published literature in the area is consistently affected by substantial experimental limitations that may affect the accuracy of translating study outcomes into practical application/s and/or design of future research. This perspective methodological review attempts to highlight these concerns and provides guidance to improve the validity, reliability, and robustness of the next generation of exercise gastroenterology research. These methodological concerns include participant screening and description, exertional and exertional heat stress load, dietary control, hydration status, food and fluid provisions, circadian variation, biological sex differences, comprehensive assessment of established markers of exercise-induced gastrointestinal syndrome, validity of gastrointestinal symptoms assessment tool, and data reporting and presentation. Standardized experimental procedures are needed for the accurate interpretation of research findings, avoiding misinterpreted (e.g., pathological relevance of response magnitude) and overstated conclusions (e.g., clinical and practical relevance of intervention research outcomes), which will support more accurate translation into safe practice guidelines.

Effect of prebiotics, probiotics, and synbiotics on gastrointestinal outcomes in healthy adults and active adults at rest and in response to exercise—A systematic literature review

“…Improvements in selectively reported measures of GIS in response to exercise following probiotic supplementation were reported in 2/5 studies. It is important to highlight the magnitude of exercise-associated gastrointestinal disturbances and differences between intervention and placebo groups in studies reporting positive effects of supplementation interventions, are modest in nature and study conclusions suggesting beneficial effects of supplementation (i.e., lower intestinal permeabiluty, endotoxaemia, cytokine responses) are to be interpreted with caution given methodological issues and concerns identified, as recently discussed in Costa et al ( 44 ). Only a limited number of studies have assessed GIS during exercise, with either minimal or no effect of probiotic supplementation observed, and with likely distorted outcomes associated with a lack of control of established confounding factors ( 79 ).…”

“…It therefore appears that there is no compelling evidence that probiotics or synbiotics exert any clinically relevant effect on resting cytokines and perhaps less so on cytokine responses to exercise at the intensities and exercise volumes observed. Whether these biotic interventions could show an attenuated systemic inflammatory effect at exercise interventions causing more activation of the immune system, as reported in Costa et al (44), remains unknown.…”

“…Participant reported data on defecation frequency and stool consistency using the Bristol Stool Rating Scale also offer supportive evidence on changes to gastrointestinal function (50). As stated, several SLR have been published in respect to biotic supplementation interventions in active adults, but none have considered the methodological issues (e.g., adequate experimental design including exertional or exertional-heat stress with or without issues with sample collection timing, experimental control of confounding factors, limitations in EIGS biomarkers, validation and reliability of GIS assessment tool) or magnitude of response of key pathophysiological markers (e.g., clinical significance of responses) (44). To date, no systematic review has comprehensively examined in-depth the effect of short or long-term pre-, pro-and syn-biotics supplementation on gastrointestinal status outcomes in healthy active adults at rest and in response to acute exercise.…”

“…In regard to the application of variables to assess the impact of pre-, pro-, and/or syn-biotic supplementation on gastrointestinal status in response to exercise stress, various biomarkers have been employed ( 44 ). Changes in gastrointestinal integrity as a result of EIGS are commonly reported in research studies using intestinal fatty acid binding protein (I-FABP), a surrogate marker for intestinal epithelial injury; or urinary or plasma claudin-3 concentration, a surrogate marker for epithelial tight gap junction function or injury.…”

An exploratory study of the management strategies reported by endurance athletes with exercise-associated gastrointestinal symptoms

“…Observational studies indicate that there may be a link between anxiety or stress and GIS development in athletes ( 50), but the effect on both functional (e.g., oro-cecal transit time, malabsorption) or integrity changes (e.g., intestinal fatty acid binding protein and cytokine responses) is largely unknown. Further research using randomized controlled cross-over or parallel trials into the use of non-dietary approaches as a strategy to manage Ex-GIS is required, in addition to applying recommended methodological approaches (51).…”