The effects of different nutritional strategies on markers of inflammation, oxidative stress and gastrointestinal stress after exercise

Abstract

Thesis abstract Exercise elicits a transient physiological stress response, involving inflammation, oxidative stress, and gastrointestinal (GI) disturbances. Regular, moderate-intensity training is associated with low-to-moderate elevations in reactive oxygen and nitrogen species (RONS) and inflammatory mediators, which play a pivotal role in cellular signalling and adaptive responses in skeletal muscle. However, prolonged or unaccustomed high-intensity exercise can provoke a more pronounced acute-phase inflammatory reaction, oxidative stress and compromise GI barrier integrity that can be detrimental to both immune and muscular recovery processes. Hence, there is a growing body of research exploring the potential of numerous nutritional approaches for modulating inflammation, oxidative stress, and gut integrity. These interventions may provide a practical advantage in athletic settings where recovery windows are limited. Among these, (poly)phenols—bioactive compounds in plant-based foods—have attracted considerable scientific attention for their potential health-promoting effects. Within this group, curcumin, a pleiotropic compound derived from turmeric, has gained particular attention due to its ability to interact with multiple antioxidant and inflammatory signalling pathways as well as its gastroprotective properties. Besides these concentrated supplements, an increasing focus has shifted toward lower-dose (poly)phenol-rich meals that are thought to deliver a complex matrix of phenolic and non-phenolic constituents, which may enhance overall bioefficacy through additive or synergistic mechanisms. While curcumin and these high (poly)phenol diets have been extensively studied in vitro or in clinical populations, evidence from human exercise studies remains limited. Accordingly, the overarching aim of this thesis was to investigate whether specific nutritional strategies—including dietary proteins and (poly)phenol-based interventions—could attenuate exercise-induced markers of inflammation, oxidative stress, and GI disturbances during the immediate hours post-exercise in healthy humans. Chapter 3 systematically evaluated the evidence from high-quality randomized controlled trials examining the effects of whole protein and commonly consumed amino acid-based supplements on biomarkers associated with inflammation and oxidative stress following exercise. The concluded evidence regarding the modulatory impact of dietary protein and amino acid supplementation on exercise-induced inflammation and oxidative stress remains insufficient and inconsistent. Consequently, the future experimental Chapters focused on exploring alternative nutritional approaches that are hypothesized to exert stronger anti-inflammatory effects. Chapter 4 aimed to explore whether short-term intake of an innovative formulation of curcumin supplementation could modify markers of inflammation and oxidative stress after intense exercise, and if this novel formulation was bioavailable. This study found that curcumin may, to some extent, modify the immune response by attenuating elevated systemic neutrophil concentrations. However, despite significantly higher plasma curcumin metabolites, the data suggested that curcumin exerted limited and inconsistent effects on other markers of inflammation and oxidative stress post-exercise, as evidenced by elevated granulocytes colony stimulating factor (G-CSF), vascular cell adhesion protein (VCAM)-1, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels in curcumin group. Chapter 5 builds upon the data from Chapter 4, by evaluating specific markers of GI disturbance or integrity post-intense exercise after acute curcumin supplementation. The findings indicated that acute curcumin supplementation may have elevated GI damage markers immediately following exercise. Chapter 6 aimed to examine whether 4 days consumption of (poly)phenols, this time whole foods breakfast, prior to muscle-damaging exercise positively influences post-exercise inflammatory and oxidative stress markers. This study reported no consistent trend in the markers measured to suggest that increasing plasma (poly)phenol levels through whole foods effectively mitigates post-exercise changes in oxidative stress and inflammation, as reflected by low glutathione peroxidase (GPX) activity and higher 8-OHdG concentrations in the supplemented group. Collectively, the findings in this thesis indicate that the ability of dietary protein, curcumin, or (poly)phenol-rich foods to modify exercise-induced markers of inflammation, oxidative stress, or GI stress (curcumin only) in humans is both limited and inconsistent. The potential benefits of these interventions in addressing post-exercise biological responses remains uncertain, and future research is needed to clarify their effectiveness in athletic populations and therefore efficacy to support recovery.