Carbohydrate and protein intake during exertional heat stress ameliorates intestinal epithelial injury and small intestine permeability

Abstract

Exertional heat stress (EHS) disturbs the integrity of the gastrointestinal tract leading to endotoxaemia and cytokinaemia, which have symptomatic and health implications. This study aimed to determine the effects of carbohydrate and protein intake during EHS on gastrointestinal integrity, symptoms, and systemic responses. Eleven (male, n = 6; female, n = 5) endurance runners completed 2 h of running at 60% maximal oxygen uptake in 35 °C ambient temperature on 3 occasions in randomised order, consuming water (WATER), 15 g glucose (GLUC), or energy-matched whey protein hydrolysate (WPH) before and every 20 min during EHS. Rectal temperature and gastrointestinal symptoms were recorded every 10 min during EHS. Blood was collected pre- and post-EHS, and during recovery to determine plasma concentrations of intestinal fatty-acid binding protein (I-FABP) as a marker of intestinal epithelial injury, cortisol, endotoxin, and inflammatory cytokines. Urinary lactulose/l-rhamnose ratio was used to measure small intestine permeability. Compared with WATER, GLUC, and WPH ameliorated EHS associated intestinal epithelial injury (I-FABP: 897 ± 478 pg·mL vs. 123 ± 197 pg·mL and 82 ± 156 pg·mL, respectively, p < 0.001) and small intestine permeability (lactulose/l-rhamnose ratio: 0.034 ± 0.014 vs. 0.017 ± 0.005 and 0.008 ± 0.002, respectively, p = 0.001). Endotoxaemia was observed post-EHS in all trials (10.2 pg·mL, p = 0.001). Post-EHS anti-endotoxin antibodies were higher (p < 0.01) and cortisol and interleukin-6 lower (p < 0.05) on GLUC than WATER only. Total and upper gastrointestinal symptoms were greater on WPH, compared with GLUC and WATER (p < 0.05), in response to EHS. In conclusion, carbohydrate and protein intake during EHS ameliorates intestinal injury and permeability. Carbohydrate also supports endotoxin clearance and reduces stress markers, while protein appears to increase gastrointestinal symptoms, suggesting that carbohydrate is a more appropriate option.

Reliability of gastrointestinal barrier integrity and microbial translocation biomarkers at rest and following exertional heat stress

“…A previous systematic review has suggested an exercise‐induced hyperthermia threshold of 38.6°C T core for GI barrier integrity loss (DSAT, I‐FABP and endotoxin) to be commonplace (>50% incidence) and of 39.0°C for GI barrier integrity loss to be universal (100% incidence; Pires et al, ). Consistently, previous research supports the notion that MT biomarkers (endotoxin) are less responsive to subtle alterations in GI barrier integrity that were otherwise detected by the DSAT or I‐FABP following exercise (March et al, ; Snipe et al, , ). Positively, no GI barrier integrity or MT biomarker displayed statistical heteroskedasticity in this EHST model, suggestive that absolute reliability was not dependent upon the magnitude of biomarker response.…”

“…This response is comparable to numerous similar duration/intensity exercise protocols, such as: 45‐to‐60 min of ~70% watt max normothermic cycling (van Wijck et al, , [61%, Δ 0.306 ng ml −1 ] 2012, [61%; Δ 0.179 ng ml −1 ] and 20–30 min of ~80% VO 2max running (Barberio et al, [46%, Δ 0.297 ng ml −1 ]; March et al, [72%; Δ 0.350 ng ml −1 ]). In comparison, far greater elevations in I‐FABP have been shown following 90–120 min of moderate‐intensity running performed in the heat (30°C; Morrison, Cheung, & Cotter, [663%; Δ 0.203–0.806 ng ml −1 ]; Snipe et al, [288%, Δ 0.897 ng ml −1 ]; 2018 [432%, Δ 1.230 ng ml −1 ]. Given the high sensitivity of I‐FABP to even minor GI injury, it is vital that known extraneous variables (e.g., prandial/hydration status, prior exercise) are tightly controlled prior to investigation.…”

“…Positively, no GI barrier integrity or MT biomarker displayed statistical heteroskedasticity in this EHST model, suggestive that absolute reliability was not dependent upon the magnitude of biomarker response. Next, biomarker analysis was limited to a single time‐point after the EHST (at termination), though this can be justified in that peak responses are consistently shown to occur at this instance in comparable exertional heat stress interventions (e.g., I‐FABP , Snipe et al, ; CLDN‐3 , Yeh et al, ; LBP , Moncada‐Jimenez et al, ; Bact./16S , March et al, ). Third, there was statistically significant systematic bias for peak T core and T body responses, which were lower (0.17°C and 0.18°C) following implementation of trial two.…”

“…The second and third visits were the main experimental trials. These were separated by 7-14 days to negate the influence of prior exertional heat stress on thermoregulatory (Barnett & Maughan, 1993) and GI barrier integrity (Snipe, Khoo, Kitic, Gibson, & Costa, 2017) responses. During both main experimental trials, participants completed an intermittent exertional heat stress test (EHST), consisting of two bouts of 40 min fixed-intensity treadmill walking (6 km h −1 and 7% gradient) in the heat (35°C and 30% relative humidity; RH).…”

Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance

“…Indeed, carbohydrate presence within the duodenum is a potent nutrient-mediator for hyperaemia in intestinal villi microvasculature (Matherson et al 2000;Rehrer et al 2005). A recent study showed that consumption of 15 g glucose before and every 20 min during running for 2 h at 60% VO 2max in 35ºC ambient temperature resulted in an abolition of exercise associated epithelial injury, compared with water alone (Snipe et al 2016b). Conversely, considering participants that reported the lowest frequency and severity of gastrointestinal symptoms did not have difficulties in tolerating the gut-challenge, but presented substantially elevated plasma I-FABP concentration, the continuation of carbohydrate provisions during the distance test may have attenuated the intestinal epithelial injury without D r a f t 21 promoting further symptoms.…”