Dietary interventions targeting the gut microbiota to support gastrointestinal and respiratory health of athletes

Parker, CJ ORCID: https://orcid.org/0000-0002-4272-1637, 2025. Dietary interventions targeting the gut microbiota to support gastrointestinal and respiratory health of athletes. PhD, Nottingham Trent University.

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Abstract

Introduction: Acute illnesses that are associated with gastrointestinal (GI) discomfort and upper respiratory symptoms (URS) are one of the major causes for medical treatment and absence in athletes. GI discomfort may occur during exercise due to increased exercise-induced GI damage and permeability, with 96% of athletes from both individual and team-based sports experiencing at least one symptom. Athletes face numerous stressors that can increase the risk of upper respiratory illness. Heavy exercise, poor sleep, poor nutrition, life stress and travel can all temporarily impair immunity and potentially increase the likelihood of infection. Large squads and the sharing of facilities can then increase the risk of transmission amongst athletes. Performing exercise in extreme environments can exacerbate these issues, which is a concern as athletes are more likely to be exposed to such climates. There is limited evidence to date on the combined influence of environmental stressors and team sport exercise on URS, GIS and gut barrier function. It is well established that the gut microbiome has a significant influence on GI health and immunity. Specific nutritional interventions may positively alter the gut microbiome and influence gut barrier function. Indeed, probiotic interventions have been shown to alleviate both GI discomfort and URS in athletic populations. However, it is unclear whether other dietary strategies that target the gut could be effective.

Thesis aims: Accordingly this thesis investigated: (i) the impact of exercising in hypoxia on blood biomarkers of GI damage, permeability, endotoxemia and discomfort, (ii) GI damage in response to a competitive soccer match and the impact of a turmeric, vitamin D and vitamin C combined dietary intervention on GI discomfort, damage and respiratory illness in professional footballers, (iii) the effects of a 24-week prebiotic trans-galactooligosaccharide (B-GOS) supplementation on GI discomfort, URS and markers of immunity in professional rugby players across a competitive season, (iv) the effects of a 6-week prebiotic B-GOS supplementation on markers of GI damage, GI discomfort, URS and markers of immunity in response to a simulated soccer match in the heat.

Experimental Results

Chapter 4: It was found that 60-min of treadmill running at 85% respiratory compensation point (RCP) caused greater GI damage when performed in normobaric hypoxia (FIO2=14.0%) than normoxia (FIO2=20.9%). Specifically, pre to post exercise ∆ plasma I-FABP was almost 2-fold greater in hypoxia than normoxia (780 ± 350 vs. 388 ± 317pg/mL) (P = 0.008). Running in hypoxia also caused greater increase in surrogate markers of GI permeability and endotoxemia as shown by higher pre to post exercise ∆ plasma claudin-3 (0.88 ± 1.66 vs. -0.65 ± 2.04ng/mL) (P = 0.005) and LBP (2659 ± 2568 vs. 607 ± 1730ng/mL) (P = 0.031) respectively. These findings were accompanied by higher GI discomfort during the hypoxia run than normoxia (10.9 ± 8.6 vs. 6.1 ± 4.4) (P=0.016). This is the first study to show that when exercise intensity is matched to environment hypoxia induces greater GI damage and discomfort. Thus, this provides preliminary evidence of a possible hypoxic and exercise mechanistic pathway. It also highlights the precautions athletes should take when exercising in hypoxic or high-altitude environments.

Chapter 5: This thesis shows for the first time that a competitive 90-minute soccer match causes GI damage as shown by elevated plasma I-FABP. It then demonstrated that the daily supplementation of a combined supplement containing 17.5 g of raw turmeric root (estimated to contain 700 mg curcumin), 1000 mg of Vitamin C, 3000 IU of Vitamin D3, and 200 mg of black pepper (estimated to contain 10 mg of piperine) for 113 days was able to reduce exercise induced GI damage following a competitive match. The combined ingredient nutritional supplement also lowered URS incidence and the severity of GI discomfort. These data highlight that the combined administration of turmeric, vitamin D3 and Vitamin C can be a potentially beneficial treatment for elite team-sport athletes, reducing the burden of acute illness and exercise-induced GI damage.

Chapter 6: Data in chapter 6 showed for first time that a 24-week prebiotic intervention was able to reduce the burden of upper respiratory illness and GI discomfort in male elite rugby union players over the course of a competitive season. Individuals assigned the daily consumption of a prebiotics galactooligosaccharide (B-GOS) (2.9/day) experienced shorter URS episodes than those assigned a placebo (7.42 ± 2.83 days vs 9.82 ± 4.05 days) (P = 0.045). They also reported a lower incidence and less severe GI discomfort (P < 0.001, P = 0.041). Individuals in the prebiotic groups also had a higher salivary IgA secretion rate than the placebo group at 24-weeks (129.23 ± 38.15 vs 90.06 ± 33.45) (P = 0.004). This study indicates that regular ingestion with a prebiotic galactooligosaccharide can be beneficial for alleviating the impact of URS and GI discomfort in elite team sport athletes.

Chapter 7: Another highly novel finding of this thesis was that a 42-day intervention of B-GOS alleviated exercise-induced GI damage following a treadmill based simulated football match in the heat. This was accompanied by a reduction in GI discomfort severity with a 17% drop in the GI severity score (P=0.021). Like the previous chapter, the B-GOS group experienced shorter URS episodes (3.4 ± 5.1 days vs 9.0 ± 5.9 days) (P = 0.025) . However, this was in conjunction with less severe URS (12 ± 16.5 vs 34.5 ± 22.5) (P = 0.029). There was also an increase in salivary IgA secretion rate in the B-GOS group but not placebo immediately post exercise at day 42 (74 ± 204 vs 106 ± 124) (P = 0.016). This shows for the first time that a prebiotic galactooligosaccharide can influence GI barrier integrity during team-based exercise in the heat, possibly alleviate exercise induced immunosuppression and confirms that it can reduce the burden of URS athletic populations.

Item Type:	Thesis
Creators:	Parker, C.J.
Contributors:	Name Role NTU ID ORCID Williams, N.C. Thesis supervisor SPO3WILLIN https://orcid.org/0000-0002-2607-4572 Sharpe, G.R. Thesis supervisor LIF3SHARPGR https://orcid.org/0000-0002-4575-2332 Hunter, K. Thesis supervisor XAA3HUNTEK https://orcid.org/0000-0002-0743-9724 Johnson, M.A. Thesis supervisor SAT3JOHNSMA https://orcid.org/0000-0002-8226-9438
Date:	May 2025
Rights:	The copyright in this work is held by the author. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required, should be directed to the author
Divisions:	Schools > School of Science and Technology
Record created by:	Laura Borcherds
Date Added:	09 Apr 2026 14:49
Last Modified:	09 Apr 2026 14:49
URI:	https://irep.ntu.ac.uk/id/eprint/55524

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