The increase in core body temperature in response to exertional-heat stress can predict exercise-induced gastrointestinal syndrome.

Utilizing metadata from existing exertional and exertional-heat stress studies, the study aimed to determine if the exercise-associated increase in core body temperature can predict the change in exercise-induced gastrointestinal syndrome (EIGS) biomarkers and exercise-associated gastrointestinal symptoms (Ex-GIS). Endurance-trained individuals completed 2 h of running exercise in temperate (21.2-30.0°C) to hot (35.0-37.2°C) ambient conditions (n = 132 trials). Blood samples were collected pre- and post-exercise to determine the change in gastrointestinal integrity biomarkers and systemic inflammatory cytokines. Physiological and thermoregulatory strain variables were assessed every 10-15 min during exercise. The strength of the linear relationship between maximal (M-Tre) and change (Δ Tre) in rectal temperature and EIGS variables was determined via Spearman's rank correlation coefficients. While the strength of prediction was determined via simple and multiple linear regression analyses dependent on screened EIGS and Ex-GIS confounding factors. Significant positive correlations between Tre maximum (M-Tre) and change (Δ Tre) with I-FABP (rs = 0.434, p < 0.001; and rs = 0.305, p < 0.001; respectively), sCD14 (rs = 0.358, p < 0.001; and rs = 0.362, p < 0.001), systemic inflammatory response profile (SIR-Profile) (p < 0.001), and total Ex-GIS (p < 0.05) were observed. M-Tre and Δ Tre significantly predicted (adjusted R2) magnitude of change in I-FABP (R2(2,123)=0.164, p < 0.001; and R2(2,119)=0.058, p = 0.011; respectively), sCD14 (R2(2,81)=0.249, p < 0.001; and R2(2,77)=0.214, p < 0.001), SIR-Profile (p < 0.001), and total Ex-GIS (p < 0.05). Strong to weak correlations were observed between M-Tre and Δ Tre with plasma concentrations of I-FABP, sCD14, SIR-Profile, and Ex-GIS in response to exercise. M-Tre and Δ Tre can predict the magnitude of these EIGS variables and Ex-GIS in response to exercise.

The impact of 48 h high carbohydrate diets with high and low FODMAP content on gastrointestinal status and symptoms in response to endurance exercise, and subsequent endurance performance.

This study investigated the effects of a high carbohydrate diet, with varied fermentable oligo-, di-, and mono-saccharide and polyol (FODMAP) content, before endurance exercise on gastrointestinal integrity, motility, and symptoms; and subsequent exercise performance. Twelve endurance athletes were provided with a 48 h high carbohydrate (mean ± SD: 12.1 ± 1.8 g kg day-1) diet on two separate occasions, composed of high (54.8 ± 10.5 g day-1) and low FODMAP (3.0 ± 0.2 g day-1) content. Thereafter, participants completed a 2 h steady-state running exercise at 60% of V ˙ O 2 max (22.9 ± 1.2 °C, 46.4 ± 7.9% RH), followed by a 1 h distance performance test. Pre-exercise and every 20 min during steady-state exercise, 100 mL maltodextrin (10% w/v) solution was consumed. A 150 mL lactulose (20 g) solution was consumed 30 min into the distance performance test to determine orocecal transit time (OCTT) during exercise. Blood was collected pre- and post exercise to determine gastrointestinal integrity biomarkers (i.e., I-FABP, sCD14, and CRP). Breath hydrogen (H2) and gastrointestinal symptoms (GIS) were determined pre-exercise, every 15 min, during and throughout recovery. No differences in gastrointestinal integrity biomarkers, OCTT, or distance completed were observed between trials. Pre-exercise total-GIS (1.3 ± 2.9 vs. 4.3 ± 4.4), gut discomfort (9.9 ± 8.1 vs. 15.8 ± 9.0), and upper-GIS (2.8 ± 2.6 vs. 5.7 ± 4.8) during exercise were less severe on high carbohydrate low FODMAP (HC-LFOD) versus high carbohydrate high FODMAP (HC-HFOD) (p < 0.05). Gut discomfort (3.4 ± 4.4 vs. 0.2 ± 0.6) and total-GIS (4.9 ± 6.8 vs. 0.2 ± 0.6) were higher during recovery on HC-LFOD versus HC-HFOD (p < 0.05). The FODMAP content of a 48 h high carbohydrate diet does not impact gastrointestinal integrity or motility in response to endurance exercise. However, a high FODMAP content exacerbates GIS before and during exercise, but this does not impact performance outcomes.

Flavonoids and phenolic acids from sugarcane: Distribution in the plant, changes during processing, and potential benefits to industry and health.

Sugarcane (Saccharum sp.) plants are grown in warmer climates throughout the world and processed to produce sugar as well as other useful byproducts such as molasses and bagasse. Sugarcane is rich in (poly)phenols, but there has been no attempt to critically evaluate the published information based on the use of suitable methodologies. The objective of this review is to evaluate the quantitative and qualitative (poly)phenolic profiles of individual parts of the sugarcane plant and its multiple industrial products, which will help develop new processes and uses for sugarcane (poly)phenols. The quantitative analysis involves the examination of extraction, concentration, and analytical techniques used in each study for each plant part and product. The qualitative analysis indicates the identification of various (poly)phenols throughout the sugarcane processing chain, using only compounds elucidated through robust analytical methodologies such as mass spectrometry or nuclear magnetic resonance. In conclusion, sugarcane (poly)phenols are predominantly flavonoids and phenolic acids. The main flavonoids, derivatives of apigenin, luteolin, and tricin, with a substantial proportion of C-glycosides, are consistently found across all phases of sugarcane processing. The principal phenolic acids reported throughout the process include chlorogenic acids, as well as ferulic and caffeic acids mostly observed after hydrolysis. The derivation of precise quantitative information across publications is impeded by inconsistencies in analytical methodologies. The presence of multiple (poly)phenols with potential benefits for industrial applications and for health suggests sugarcane could be a useful provider of valuable compounds for future use in research and industrial processes.

Does Age Influence Gastrointestinal Status Responses to Exertional-heat Stress?

This meta-data exploration aimed to determine the impact of exertional-heat stress (EHS) on gastrointestinal status of masters age and young adult endurance athletes. Sixteen MASTERS (mean: 44y) and twenty-one YOUNG (26y) recreational endurance athletes completed 2 h of running at 60% ˙V O2max in 35˚C ambient conditions. Blood samples were collected pre-, immediately and 1 h post-EHS, and analyzed for markers of exercise-induced gastrointestinal syndrome (EIGS). Thermo-physiological measures and gastrointestinal symptoms (GIS) were recorded every 10-20 min during EHS. Peak Δ pre- to post-EHS did not substantially differ (p>0.05) between MASTERS and YOUNG for intestinal epithelial injury [I-FABP: 1652pg/ml vs. 1524pg/ml, respectively], bacterial endotoxic translocation [sCD14: -0.09µg/mL vs. 0.84µg/mL, respectively], lipopolysaccharide-binding protein [LBP: 0.26µg/mL vs. 1.76µg/mL, respectively], and systemic inflammatory response profile (SIR-Profile: 92.0arb.unit vs. 154arb.unit, respectively). A significantly higher peak Δ pre- to post-EHS in endogenous endotoxin anti-body IgM (p=0.042), and pro-inflammatory cytokine IL-1ß (p=0.038), was observed in YOUNG compared to MASTERS. No difference was observed between incidence (81% and 80%, respectively) and severity (summative accumulation: 21 and 30, respectively) of reported GIS during EHS between MASTERS and YOUNG. Pathophysiology of EIGS in response to EHS does not substantially differ with age progression, since masters and younger adult endurance athletes responded comparably.

Exertional Stress-induced Pathogenic Luminal Content Translocation - Friend or Foe?

The incidence of perturbed gastrointestinal integrity, as well as resulting systemic immune responses and gastrointestinal symptoms, otherwise known as exercised-induced gastrointestinal syndrome (EIGS), is common among individuals who partake in prolonged exercise. EIGS may cause the translocation of pathogenic material, including whole bacteria and bacterial endotoxins, from the lumen into circulation, which may progress into clinical consequences such as sepsis, and potentially subsequent fatality. However, further investigation is warranted to assess the possibility of food allergen and/or digestive enzyme luminal to circulatory translocation in response to exercise, and the clinical consequences. Findings from this narrative literature review demonstrate evidence that whole bacteria and bacterial endotoxins translocation from the gastrointestinal lumen to systemic circulation occurs in response to exercise stress, with a greater propensity of translocation occurring with accompanying heat exposure. It has also been demonstrated that food allergens can translocate from the lumen to systemic circulation in response to exercise stress and initiate anaphylaxis. To date, no research investigating the effect of exercise on the translocation of digestive enzymes from the lumen into systemic circulation exists. It is evident that EIGS and consequential pathogenic translocation presents life-threatening clinical implications, warranting the development and implementation of effective management strategies in at-risk populations.

Effect of Personalized Sodium Replacement on Fluid and Sodium Balance and Thermophysiological Strain During and After Ultraendurance Running in the Heat.

PURPOSE: To investigate the effect of personalized sweat sodium replacement on drinking behavior, sodium and water balance, and thermophysiological responses during and after ultraendurance running in hot conditions. METHODS: Nine participants (7 male, 2 female) completed two 5-hour treadmill runs (60% maximum oxygen uptake, 30°C ambient temperature), in a double-blind randomized crossover design, consuming sodium chloride (SODIUM) capsules to replace 100% of previously assessed losses or placebo (PLACEBO). Fluid was consumed ad libitum. RESULTS: No effect of SODIUM was observed for ad libitum fluid intake or net fluid balance (P > .05). Plasma sodium concentration increased in both trials, but to a greater extent in SODIUM at 2.5 hours (mean [SD]: 4 [4] mmol·L-1 vs 1 [5] mmol·L-1; P < .05) and postexercise (4 [3] mmol·L-1 vs 1 [5] mmol·L-1; P < .05). Plasma volume change was not different between trials (P > .05) but was strongly correlated with sodium balance in SODIUM (r = .880, P < .01). No effect of sodium replacement was observed for heart rate, rectal temperature, thermal comfort, perceived exertion, or physiological strain index. During the 24 hours postexercise, ad libitum fluid intake was greater following SODIUM (2541 [711] mL vs 1998 [727] mL; P = .04), as was urinary sodium excretion (NaCl: 66 [35] mmol, Pl: 21 [12] mmol; P < .01). CONCLUSIONS: Personalized sweat sodium replacement during ultraendurance running in hot conditions, with ad libitum fluid intake, exacerbated the rise in plasma sodium concentration compared to no sodium replacement but did not substantially influence overall body-water balance or thermophysiological strain. A large sodium deficit incurred during exercise leads to substantial renal sodium conservation postexercise.

Plasma measurements of the dual sugar test reveal carbohydrate immediately alleviates intestinal permeability caused by exertional heat stress.

The aim of this set of randomised cross-over studies was to determine the impact of progressive heat exposure and carbohydrate or protein feeding during exertional stress on small intestine permeability using a dual sugar test. In our previous work, and typically in the field, recovery of lactulose and l-rhamnose is measured cumulatively in urine. This follow-up study exploits our novel high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) protocol to accurately quantify the sugars in plasma. Endurance-trained participants completed experimental trial A (ET-A; n = 8), consisting of 2 h running at 60% V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ in temperate, warm and hot ambient conditions, and/or experimental trial B (ET-B; n = 9), consisting of 2 h running at 60% V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ in the heat while consuming water, carbohydrate or protein. Blood samples were collected and plasma lactulose (L) and l-rhamnose (R) appearance, after dual sugar solution ingestion at 90 min of exercise, was quantified by HPAEC-PAD to measure plasma L/R and reveal new information about intestinal permeability immediately post-exercise and during recovery. In ET-A, plasma L/R increased immediately post-exercise in hot compared with temperate and warm conditions, while, in ET-B, carbohydrate alleviated this, and this information was otherwise missed when measuring urine L/R. Consuming carbohydrate or protein before and during exercise attenuated small intestine permeability throughout recovery from exertional heat stress. We recommend using the dual sugar test with quantification of plasma sugars by HPAEC-PAD at intervals to maximise intestinal permeability data collection in exercise gastroenterology research, as this gives additional information compared to urinary measurements. KEY POINTS: Intestinal permeability is typically assessed using a dual sugar test, by administering a drink containing non-metabolisable sugars (e.g. lactulose (L) and l-rhamnose (R)) that can enter the circulation by paracellular translocation when the epithelium is compromised, and are subsequently measured in urine. We demonstrate that our recently developed ion chromatography protocol can be used to accurately quantify the L/R ratio in plasma, and that measuring L/R in plasma collected at intervals during the post-exercise recovery period reveals novel acute response information compared to measuring 5-h cumulative urine L/R. We confirm that exercising in hot ambient conditions increases intestinal epithelial permeability immediately after exercise, while consuming carbohydrate or protein immediately before and during exercise attenuates this. We recommend using our dual sugar absorption test protocol to maximise intestinal epithelial permeability data collection in exercise gastroenterology research and beyond.

The Impact of a Short-Term Ketogenic Low-Carbohydrate High-Fat Diet on Biomarkers of Intestinal Epithelial Integrity and Gastrointestinal Symptoms.

Endurance exercise can disturb intestinal epithelial integrity, leading to increased systemic indicators of cell injury, hyperpermeability, and pathogenic translocation. However, the interaction between exercise, diet, and gastrointestinal disturbance still warrants exploration. This study examined whether a 6-day dietary intervention influenced perturbations to intestinal epithelial disruption in response to a 25-km race walk. Twenty-eight male race walkers adhered to a high carbohydrate (CHO)/energy diet (65% CHO, energy availability = 40 kcal·kg FFM-1·day-1) for 6 days prior to a Baseline 25-km race walk. Athletes were then split into three subgroups: high CHO/energy diet (n = 10); low-CHO, high-fat diet (LCHF: n = 8; <50 g/day CHO, energy availability = 40 kcal·kg FFM-1·day-1); and low energy availability (n = 10; 65% CHO, energy availability = 15 kcal·kg FFM-1·day-1) for a further 6-day dietary intervention period prior to a second 25-km race walk (Adaptation). During both trials, venous blood was collected pre-, post-, and 1 hr postexercise and analyzed for markers of intestinal epithelial disruption. Intestinal fatty acid-binding protein concentration was significantly higher (twofold increase) in response to exercise during Adaptation compared to Baseline in the LCHF group (p = .001). Similar findings were observed for soluble CD14 (p < .001) and lipopolysaccharide-binding protein (p = .003), where postexercise concentrations were higher (53% and 36%, respectively) during Adaptation than Baseline in LCHF. No differences in high CHO/energy diet or low energy availability were apparent for any blood markers assessed (p > .05). A short-term LCHF diet increased intestinal epithelial cell injury in response to a 25-km race walk. No effect of low energy availability on gastrointestinal injury or symptoms was observed.

The Impact of a 24-h Low and High Fermentable Oligo- Di- Mono-Saccharides and Polyol (FODMAP) Diet on Plasma Bacterial Profile in Response to Exertional-Heat Stress.

Exertional-heat stress (EHS) compromises intestinal epithelial integrity, potentially leading to the translocation of pathogenic agents into circulation. This study aimed to explore the impact of EHS on the systemic circulatory bacterial profile and to determine the impact of a short-term low (LFOD) and high (HFOD) fermentable oligo- di- mono-saccharide and polyol dietary intervention before EHS on this profile. Using a double-blind randomized cross-over design, thirteen endurance runners (n = 8 males, n = 5 females), with a history of exercise-associated gastrointestinal symptoms (Ex-GIS), consumed a 24 h LFOD and HFOD before 2 h running at 60% V.O2max in 35.6 °C. Blood and fecal samples were collected pre-EHS to determine plasma microbial DNA concentration, and sample bacteria and short chain fatty acid (SCFA) profiles by fluorometer quantification, 16S rRNA amplicon gene sequencing, and gas chromatography, respectively. Blood samples were also collected post-EHS to determine changes in plasma bacteria. EHS increased plasma microbial DNA similarly in both FODMAP trials (0.019 ng·µL-1 to 0.082 ng·µL-1) (p < 0.01). Similar pre- to post-EHS increases in plasma Proteobacteria (+1.6%) and Firmicutes (+0.6%) phyla relative abundance were observed in both FODMAP trials. This included increases in several Proteobacteria genus (Delftia and Serratia) groups. LFOD presented higher fecal Firmicutes (74%) and lower Bacteroidota (10%) relative abundance pre-EHS, as a result of an increase in Ruminococcaceae and Lachnospiraceae family and respective genus groups, compared with HFOD (64% and 25%, respectively). Pre-EHS plasma total SCFA (p = 0.040) and acetate (p = 0.036) concentrations were higher for HFOD (188 and 178 µmol·L-1, respectively) vs. LFOD (163 and 153 µmol·L-1, respectively). Pre-EHS total fecal SCFA concentration (119 and 74 µmol·g-1; p < 0.001), including acetate (74 and 45 µmol·g-1; p = 0.001), butyrate (22 and 13 µmol·g-1; p = 0.002), and propionate (20 and 13 µmol·g-1; p = 0.011), were higher on HFOD vs LFOD, respectively. EHS causes the translocation of whole bacteria into systemic circulation and alterations to the plasma bacterial profile, but the FODMAP content of a 24 h diet beforehand does not alter this outcome.

Carbohydrate knowledge, beliefs, and intended practices, of endurance athletes who report exercise-associated gastrointestinal symptoms.

This study aimed to explore carbohydrate (CHO) knowledge, beliefs, and intended practices of endurance athletes who experience exercise-associated gastrointestinal symptoms (Ex-GIS) compared to those without Ex-GIS. A validated online questionnaire was completed by endurance athletes (n = 201) participating in >60 min of exercise that present with Ex-GIS (n = 137) or without (n = 64). Descriptive statistics were used for parametric and non-parametric data with appropriate significance tests. Associations between categorical data were assessed by Chi-square analysis, and post-hoc Bonferroni tests were applied when significant. A content analysis of open-ended responses was grouped into themes, and quantitative statistics were applied. Participants included runners (n = 114, 57%), triathletes (n = 43, 21%) and non-running sports (n = 44, 21%) who participate in recreational competitive (n = 74, 37%), recreational non-competitive (n = 64, 32%), or competitive regional, national, or international levels (n = 63, 31%). Athletes correctly categorized CHO (x̄ = 92-95%) and non-CHO (x̄ = 88-90%) food and drink sources. On a Likert scale of 1 (strongly disagree) to 5 (strongly agree) athletes typically agree or strongly agree that consuming CHO around key training sessions and competitions enhances athletic performance [median = 4 (IQR, 4-5)], and they intend to consume more CHO around exercise [median = 3 (IQR, 2-3)]. No differences in beliefs and intentions were found among athletes with or without Ex-GIS. To enhance athletic performance, most endurance athletes intend to consume more CHO around exercise. Adequate knowledge of CHO-containing food sources was apparent; however, specific CHO ingestion practices remain to be verified.

Amino Acid-Based Beverage Interventions Ameliorate Exercise-Induced Gastrointestinal Syndrome in Response to Exertional-Heat Stress: The Heat Exertion Amino Acid Technology (HEAAT) Study.

The study aimed to determine the effects of two differing amino acid beverage interventions on biomarkers of intestinal epithelial integrity and systemic inflammation in response to an exertional-heat stress challenge. One week after the initial assessment, participants (n = 20) were randomly allocated to complete two exertional-heat stress trials, with at least 1 week washout. Trials included a water control trial (CON), and one of two possible amino acid beverage intervention trials (VS001 or VS006). On VS001 (4.5 g/L) and VS006 (6.4 g/L), participants were asked to consume two 237-ml prefabricated doses daily for 7 days before the exertional-heat stress, and one 237-ml dose immediately before, and every 20 min during 2-hr running at 60% maximal oxygen uptake in 35 °C ambient conditions. A water volume equivalent was provided on CON. Whole blood samples were collected pre-, immediately post-, 1 and 2 hr postexercise, and analyzed for plasma concentrations of cortisol, intestinal fatty acid protein, soluble CD14, and immunoglobulin M (IgM) by ELISA, and systemic inflammatory cytokines by multiplex. Preexercise resting biomarker concentrations for all variables did not significantly differ between trials (p > .05). A lower response magnitude for intestinal fatty acid protein (mean [95% CI]: 249 [60, 437] pg/ml, 900 [464, 1,336] pg/ml), soluble CD14 (-93 [-458, 272] ng/ml, 12 [-174, 197] ng/ml), and IgM (-6.5 [-23.0, 9.9] MMU/ml, -10.4 [-16.2, 4.7] MMU/ml) were observed on VS001 and V006 compared with CON (p < .05), respectively. Systemic inflammatory response profile was lower on VS001, but not VS006, versus CON (p < .05). Total gastrointestinal symptoms did not significantly differ between trials. Amino acid beverages' consumption (i.e., 4.5-6.4 g/L), twice daily for 7 days, immediately before, and during exertional-heat stress ameliorated intestinal epithelial integrity and systemic inflammatory perturbations associated with exercising in the heat, but without exacerbating gastrointestinal symptoms.

The Effect of Gut-Training and Feeding-Challenge on Markers of Gastrointestinal Status in Response to Endurance Exercise: A Systematic Literature Review.

BACKGROUND: Nutrition during exercise is vital in sustaining prolonged activity and enhancing athletic performance; however, exercise-induced gastrointestinal syndrome (EIGS) and exercise-associated gastrointestinal symptoms (Ex-GIS) are common issues among endurance athletes. Despite this, there has been no systematic assessment of existing trials that examine the impact of repetitive exposure of the gastrointestinal tract to nutrients before and/or during exercise on gastrointestinal integrity, function, and/or symptoms. OBJECTIVE: This systematic literature review aimed to identify and synthesize research that has investigated the impact of 'gut-training' or 'feeding-challenge' before and/or during exercise on markers of gastrointestinal integrity, function, and symptoms. METHODS: Five databases (Ovid MEDLINE, EMBASE, CINAHL Plus, Web of Science Core Collection, and SPORTDiscus) were searched for literature that focused on gut-training or feeding-challenge before and/or during exercise that included EIGS and Ex-GIS variables. Quality assessment was conducted in duplicate and independently using the Cochrane Collaboration's risk-of-bias (RoB 2) tool. RESULTS: Overall, 304 studies were identified, and eight studies were included after screening. Gut-training or feeding-challenge interventions included provision of carbohydrates only (n = 7) in various forms (e.g., gels or liquid solutions) during cycling or running, or carbohydrate with protein (n = 1) during intermittent exercise, over a varied duration (4-28 days). Gut discomfort decreased by an average of 47% and 26% with a 2-week repetitive carbohydrate feeding protocol (n = 2) and through repeated fluid ingestion over five trials (n = 1), respectively. Repetitive carbohydrate feeding during exercise for 2 weeks resulted in the reduction of carbohydrate malabsorption by 45-54% (n = 2), but also led to no significant change (n = 1). The effect of gut-training and feeding-challenges on the incidence and severity of Ex-GIS were assessed using different tools (n = 6). Significant improvements in total, upper, and lower gastrointestinal symptoms were observed (n = 2), as well as unclear results (n = 4). No significant changes in gastric emptying rate (n = 2), or markers of intestinal injury and permeability were found (n = 3). Inconclusive results were found in studies that investigated plasma inflammatory cytokine concentration in response to exercise with increased carbohydrate feeding (n = 2). CONCLUSIONS: Overall, gut-training or feeding-challenge around exercise may provide advantages in reducing gut discomfort, and potentially improve carbohydrate malabsorption and Ex-GIS, which may have exercise performance implications.

Reliability of pathophysiological markers reflective of exercise-induced gastrointestinal syndrome (EIGS) in response to 2-h high-intensity interval exercise: A comprehensive methodological efficacy exploration.

The study aimed to determine the test-retest reliability of exercise-induced gastrointestinal syndrome (EIGS) biomarkers, and assess the association of pre-exercise short chain fatty acid (SCFA) concentration with these biomarkers in response to prolonged strenuous exercise. Thirty-four participants completed 2 h of high-intensity interval training (HIIT) on two separate occasions with at least 5-days washout. Blood samples were collected pre- and post-exercise, and analysed for biomarkers associated with EIGS [i.e., cortisol, intestinal fatty-acid binding protein (I-FABP), sCD14, lipopolysaccharide binding protein (LBP), leukocyte counts, in-vitro neutrophil function, and systemic inflammatory cytokine profile]. Fecal samples were collected pre-exercise on both occasions. In plasma and fecal samples, bacterial DNA concentration was determined by fluorometer quantification, microbial taxonomy by 16S rRNA amplicon sequencing, and SCFA concentration by gas-chromatography. In response to exercise, 2 h of HIIT modestly perturbed biomarkers indicative of EIGS, including inducing bacteremia (i.e., quantity and diversity). Reliability analysis using comparative tests, Cohen's d, two-tailed correlation, and intraclass correlation coefficient (ICC) of resting biomarkers presented good-to-excellent for IL-1ra (r = 0.710, ICC = 0.92), IL-10 (r = 0.665, ICC = 0.73), cortisol (r = 0.870, ICC = 0.87), and LBP (r = 0.813, ICC = 0.76); moderate for total (r = 0.839, ICC = 0.44) and per cell (r = 0.749, ICC = 0.54) bacterially-stimulated elastase release, IL-1ß (r = 0.625, ICC = 0.64), TNF-α (r = 0.523, ICC = 0.56), I-FABP (r = 0.411, ICC = 0.21), and sCD14 (r = 0.409, ICC = 0.38), plus fecal bacterial α-diversity; and poor for leukocyte (r = 0.327, ICC = 0.33) and neutrophil (r = 0.352, ICC = 0.32) counts. In addition, a medium negative correlation was observed between plasma butyrate and I-FABP (r = -0.390). The current data suggest a suite of biomarkers should be used to determine the incidence and severity of EIGS. Moreover, determination of plasma and/or fecal SCFA may provide some insight into the mechanistic aspects of EIGS instigation and magnitude in response to exercise.

Impact of exercise duration on gastrointestinal function and symptoms.

The study aimed to determine the impact of exercise duration on gastrointestinal functional responses and gastrointestinal symptoms (GISs) in response to differing exercise durations. Endurance runners (n = 16) completed three trials on separate occasions, randomized to 1 h (1-H), 2 h (2-H), and 3 h (3-H) of running at 60% V̇o2max in temperate ambient temperature. Orocecal transit time (OCTT) was determined by lactulose challenge, with concomitant breath hydrogen (H2) determination. Gastric slow wave activity was recorded using cutaneous electrogastrography (cEGG) before and after exertion. GIS was determined using a modified visual analog scale (mVAS). OCTT response was classified as very slow on all trials (∼93-101 min) with no trial difference observed (P = 0.895). Bradygastria increased postexercise on all trials (means ± SD: 1-H: 10.9 ± 11.7%, 2-H: 6.2 ± 9.8%, and 3-H: 13.2 ± 21.4%; P < 0.05). A reduction in the normal gastric slow wave activity (2-4 cycles/min) was observed postexercise on 1-H only (-10.8 ± 17.6%; P = 0.039). GIS incidence and gut discomfort was higher on 2-H (81% and 12 counts) and 3-H (81% and 18 counts), compared with 1-H (69% and 6 counts) (P = 0.038 and P = 0.006, respectively). Severity of gut discomfort, total-GIS, upper-GIS, and lower-GIS increased during exercise on all trials (P < 0.05). Steady-state exercise in temperate ambient conditions for 1 h, 2 h, and 3 h instigates perturbations in gastric slow wave activity compared with rest and hampers OCTT, potentially explaining the incidence and severity on exercise-associated GIS.NEW & NOTEWORTHY Exercise stress per se appears to instigate perturbations to gastric myoelectrical activity, resulting in an increase in bradygastria frequency, inferring a reduction in gastric motility. The perturbations to gastrointestinal functional responses instigated by exercise per se, likely contribute to the high incidence and severity level of exercise-associated gastrointestinal symptoms. Cutaneous electrogastrography is not commonly used in exercise gastroenterology research, however, may be a useful aid in providing an overall depiction of gastrointestinal function. Particularly relating to gastrointestinal motility and concerning gastroparesis.

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.

Introduction: A systematic literature search was undertaken to assess the impact of pre-, pro-, and syn-biotic supplementation on measures of gastrointestinal status at rest and in response to acute exercise. Methods: Six databases (Ovid MEDLINE, EMBASE, Cinahl, SportsDISCUS, Web of Science, and Scopus) were used. Included were human research studies in healthy sedentary adults, and healthy active adults, involving supplementation and control or placebo groups. Sedentary individuals with non-communicable disease risk or established gastrointestinal inflammatory or functional diseases/disorders were excluded. Results: A total of n = 1,204 participants were included from n = 37 papers reported resting outcomes, and n = 13 reported exercise-induced gastrointestinal syndrome (EIGS) outcomes. No supplement improved gastrointestinal permeability or gastrointestinal symptoms (GIS), and systemic endotoxemia at rest. Only modest positive changes in inflammatory cytokine profiles were observed in n = 3/15 studies at rest. Prebiotic studies (n = 4/5) reported significantly increased resting fecal Bifidobacteria, but no consistent differences in other microbes. Probiotic studies (n = 4/9) increased the supplemented bacterial species-strain. Only arabinoxylan oligosaccharide supplementation increased total fecal short chain fatty acid (SCFA) and butyrate concentrations. In response to exercise, probiotics did not substantially influence epithelial injury and permeability, systemic endotoxin profile, or GIS. Two studies reported reduced systemic inflammatory cytokine responses to exercise. Probiotic supplementation did not substantially influence GIS during exercise. Discussion: Synbiotic outcomes resembled probiotics, likely due to the minimal dose of prebiotic included. Methodological issues and high risk of bias were identified in several studies, using the Cochrane Risk of Bias Assessment Tool. A major limitation in the majority of included studies was the lack of a comprehensive approach of well-validated biomarkers specific to gastrointestinal outcomes and many included studies featured small sample sizes. Prebiotic supplementation can influence gut microbial composition and SCFA concentration; whereas probiotics increase the supplemented species-strain, with minimal effect on SCFA, and no effect on any other gastrointestinal status marker at rest. Probiotic and synbiotic supplementation does not substantially reduce epithelial injury and permeability, systemic endotoxin and inflammatory cytokine profiles, or GIS in response to acute exercise.

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

This exploratory study investigated endurance athletes self-reported exercise-associated gastrointestinal symptoms (Ex-GIS) and associated strategies to manage symptomology. Adult endurance athletes with a history of Ex-GIS (n = 137) participating in events ≥ 60 min completed an online validated questionnaire. Respondents included runners (55%, n = 75), triathletes (22%, n = 30), and non-running sports (23%, n = 32), participating at a recreationally competitive (37%, n = 51), recreationally non-competitive (32%, n = 44), and competitive regional/national/international (31%, n = 42) levels. Athletes identified when Ex-GIS developed most frequently either around training (AT), around competitions (AC), or equally around both training (ET) and competitions (EC). Athletes reported the severity of each symptom before, during, and after exercise. Athletes predominantly categorized Ex-GIS severity as mild (< 5/10) on a 0 (no symptoms) to 10 (extremely severe symptoms) visual analog symptomology scale. The Friedman test and post hoc analysis with Wilcoxon signed rank test was conducted with a Bonferroni correction applied to determine differences between repeated measures. The only severe symptom of significance was the urge to defecate during training in the ET group (Z = -0.536, p = 0.01). Ex-GIS incidence was significantly higher during training and competitions in all categories. A content review of self-reported strategies (n = 277) to reduce Ex-GIS indicated popular dietary strategies were dietary fiber reduction (15.2%, n = 42), dairy avoidance (5.8%, n = 16), and a low fermentable oligosaccharides, monosaccharides, and polyols (FODMAP) diet (5.4%, n = 15). In contrast, non-dietary strategies included the use of medications (4.7%, n = 13) and relaxation/meditation (4.0%, n = 11). On a Likert scale of 1-5, the most successful dietary strategies implemented were dietary fiber reduction (median = 4, IQR = 4, 5), low FODMAP diets (median = 4, IQR = 4, 5), dairy-free diets (median = 4, IQR = 4, 5), and increasing carbohydrates (median = 4, IQR = 3, 4). Accredited practicing dietitians were rated as the most important sources of information for Ex-GIS management (n = 29). Endurance athletes use a variety of strategies to manage their Ex-GIS, with dietary manipulation being the most common.

Does exertional heat stress impact gastrointestinal function and symptoms?

OBJECTIVES: Exertional-heat stress generates a thermoregulatory strain that exacerbates splanchnic hypoperfusion and sympathetic drive, but the effects on gastrointestinal function are poorly defined. The study aimed to determine the effects of exertional-heat stress on gastric myoelectrical activity, orocecal transit time (OCTT), and gastrointestinal symptoms (GIS). DESIGN: Randomised cross-over study. METHODS: Endurance runners (n = 16) completed 2 h of running at 60 % V̇O2max in 35 °C (HOT) and 22 °C (TEMP) ambient conditions. Surface electrogastrography (cEGG) was recorded pre- and post-exercise to determine gastric myoelectrical activity, a lactulose challenge was used to determine OCTT, and GIS were recorded using a modified visual analogue scale tool. RESULTS: Post-exercise Tre [HOT:38.8(38.5 to 39.0)°C and TEMP:38.1(37.8 to 38.4)°C] and Δ Tre [HOT:2.2(2.0 to 2.4)°C and TEMP:1.5(1.2 to 1.8)°C] was higher on HOT compared to TEMP (p < 0.001). Normal gastric myoelectrical cycle frequency reduced (p = 0.010) on HOT [-11.7(-20.8 to -2.6)%], but this decrease did not differ (p = 0.058) from TEMP [-2.7(-8.3 to 3.0)%]. Bradygastria increased post-exercise on both trials (HOT:11.3(2.3 to 20.4)%, p = 0.030; and TEMP:7.4(2.1 to 12.6)%, p = 0.009). OCTT did not differ between trials (p = 0.864) with transit response classified as very slow on both HOT (99(68 to 131)min) and TEMP (98(74 to 121)min). GIS incidence was higher on HOT (88 %) compared to TEMP (81 %), in accordance with greater total-GIS and upper-GIS severity (p = 0.005 and p = 0.033, respectively). CONCLUSIONS: Running for 2 h at 60 % V̇O2max in either hot or temperate ambient conditions instigates perturbations in myoelectrical activity and OCTT, with GIS incidence and severity greater in hot conditions.

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

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.

The impact of exercise modality on exercise-induced gastrointestinal syndrome and associated gastrointestinal symptoms.

OBJECTIVES: This study aimed to determine the impact of running and cycling exercise modalities on the magnitude of exercise-induced gastrointestinal syndrome (EIGS) and associated gastrointestinal symptoms (GIS). DESIGN: Parallel group trial design. METHODS: Twenty-eight endurance athletes (male n = 14, female n = 14) completed 2 h running at 55 % of maximal oxygen uptake or cycling at 55 % of maximal aerobic power in Tamb 35 °C and 22 % RH. Pre- and post-exercise blood samples were collected and analysed for markers of intestinal epithelial integrity perturbations (i.e., plasma intestinal fatty acid protein (I-FABP), soluble (s)CD14, and lipopolysaccharide binding protein (LBP)) and systemic inflammatory cytokines (i.e., plasma IL-1ß, TNFα, IL-10, and IL-1ra). GIS were assessed pre-exercise and every 10 min during exercise. RESULTS: Exercise-associated Δ for plasma I-FABP (191 and 434 pg‧ml-1) and LBP (-1228 and 315 ng‧ml-1) did not differ between running and cycling, respectively; however for sCD14 was higher (p = 0.030) on cycling (116 ng‧ml-1) vs running (96 ng‧ml-1). There were no differences in absolute pre- and post-exercise systemic inflammatory cytokine concentration, with large individual variation observed. Exercise-associated plasma TNF-α, (p = 0.041) and IL-10 (p = 0.019) responses were greater in running than cycling, but did not lead to a greater systemic inflammatory response profile (p = 0.305) between running (5.0arb.units) and cycling (-2.5arb.units). Although greater GIS incidence occurred in running (44 %) compared with cycling (25 %), there was no difference between groups for GIS severity. CONCLUSIONS: When running and cycling exercise is performed with similar duration, intensity, ambient conditions, and with confounder control, the exercise modality does not substantially impact the magnitude of EIGS or associated GIS severity.

Short-Term Very High Carbohydrate Diet and Gut-Training Have Minor Effects on Gastrointestinal Status and Performance in Highly Trained Endurance Athletes.

We implemented a multi-pronged strategy (MAX) involving chronic (2 weeks high carbohydrate [CHO] diet + gut-training) and acute (CHO loading + 90 g·h−1 CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON) in two groups of athletes. Nineteen elite male race walkers (MAX: 9; CON:10) undertook a 26 km race-walking session before and after the respective interventions to investigate gastrointestinal function (absorption capacity), integrity (epithelial injury), and symptoms (GIS). We observed considerable individual variability in responses, resulting in a statistically significant (p < 0.001) yet likely clinically insignificant increase (Δ 736 pg·mL−1) in I-FABP after exercise across all trials, with no significant differences in breath H2 across exercise (p = 0.970). MAX was associated with increased GIS in the second half of the exercise, especially in upper GIS (p < 0.01). Eighteen highly trained male and female distance runners (MAX: 10; CON: 8) then completed a 35 km run (28 km steady-state + 7 km time-trial) supported by either a slightly modified MAX or CON strategy. Inter-individual variability was observed, without major differences in epithelial cell intestinal fatty acid binding protein (I-FABP) or GIS, due to exercise, trial, or group, despite the 3-fold increase in exercise CHO intake in MAX post-intervention. The tight-junction (claudin-3) response decreased in both groups from pre- to post-intervention. Groups achieved a similar performance improvement from pre- to post-intervention (CON = 39 s [95 CI 15−63 s]; MAX = 36 s [13−59 s]; p = 0.002). Although this suggests that further increases in CHO availability above current guidelines do not confer additional advantages, limitations in our study execution (e.g., confounding loss of BM in several individuals despite a live-in training camp environment and significant increases in aerobic capacity due to intensified training) may have masked small differences. Therefore, athletes should meet the minimum CHO guidelines for training and competition goals, noting that, with practice, increased CHO intake can be tolerated, and may contribute to performance outcomes.