Investigating the altered human metabolome induced by a marathon and the recovery thereof
Although moderate physical activity is substantially beneficial to human health, continuous participation in endurance running (≥5 km), has been associated with various adverse physiological and immunological effects. Despite these effects, endurance running is still considered a popular global pass time that has rapidly evolved into a highly competitive sport, classified as either a half-marathon (21 km), marathon (42 km) or ultra-marathon (≥42 km). Considering that recovery is a key component in athletic performance, previous research approaches have been directed towards identifying more cost-effective, readily available recovery approaches, such as functional foods (beetroot, cherry, pomegranate, bananas, etc.). These foods, especially beetroot, are rich in antioxidants and possess potent radical scavenging properties, that may aid in the physiological and immunological post-training recovery of athletes. Despite the well-characterised nature of the aforementioned effects and the recovery thereof, very limited literature exists pertaining to the holistic metabolic adaptations that may arise due to participation in endurance races and how these may recover with and without the intervention of recovery aids. Since metabolomics not only elucidates the effects of an intervention at metabolic level, but also provides a representation or prediction of the organism’s phenotypic state at a specific point in time, it is an excellent research approach to fill these voids. Metabolomics is defined as the comprehensive identification and quantification of the small metabolites (<1500 Da) involved in the metabolic reactions associated with cell growth and function in a biological sample, using high-throughput separation systems, in conjunction with various statistical approaches. As such, the current investigation aimed to: (1) better characterise the metabolic adaptations induced by a marathon, (2) investigate the unaided or natural metabolic recovery trend thereof, and (3) determine whether beetroot juice ingestion may expedite this recovery process in athletes within 48 h post-marathon. For this double-blinded placebo-controlled study, serum samples from 31 athletes were obtained 24 h before (pre-marathon), immediately after, as well as 24 h and 48 h after completing the Druridge Bay Marathon. During the post-race recovery period (i.e. 24 h and 48 h post-marathon), these athletes were subdivided into beetroot (n=15) and placebo (n=16) ingesting cohorts, based on the supplement received (± three times a day). All samples were extracted using a total metabolome extraction and analysed using an untargeted two-dimensional gas chromatography time-of-flight mass spectrometry-based metabolomics approach. Based on the comparison of the pre-marathon and immediately post-marathon serum metabolite profiles of athletes (n=31), it was clear that a marathon induces a metabolic shift between various fuel substrate pathways, as evident by the elevated concentrations of carbohydrates, fatty acids, tricarboxylic acid cycle intermediates and ketones, along with a reduction in amino acids. Additionally, elevated odd-chain fatty acids and α-hydroxy acids indicated the utilisation of α-oxidation and autophagy as alternative energy-producing mechanisms. Adaptations in various gut microbe-associated markers were also observed and correlated with the metabolic flexibility of the athlete. Surprisingly, when investigating the unaided metabolic recovery trend of placebo-ingesting athletes (n=16; comparing immediately post-marathon, 24 h and 48 h post-marathon profiles), the metabolic data indicated recovery to pre-marathon-related state within 24 h post-marathon, with the exception of xylose which recovered within 48 h. This may be explained by a reduction in energy requirements during recovery and the subsequent downregulation of fuel substrate catabolism, resulting in the activation of glycogenesis, uridine-dependent nucleotide synthesis, protein synthesis, and the reduction of cellular autophagy. Finally, when determining the effects of beetroot juice supplementation on the recovery of athletes (n=15; comparing immediately post-marathon, 24 h and 48 h post-marathon profiles), a similar recovery trend to that of the placebo cohort was observed. Although a few significant, albeit small, intervention and/or interaction associated metabolic fluctuations were identified between the cohorts, the majority of these presented a considerable amount of post-marathon inter-cohort variation. As such, only metabolites with a large practical significance within the recovery period was considered to be pertinent in determining the efficacy of beetroot juice supplementation. These metabolites (n=4) were predominantly associated with beetroot constituents and the microbial fermentation thereof, with little to no apparent value to the immediate metabolic recovery of the athletes. Considering this, and the global metabolic recovery trends of the two opposing cohorts, beetroot ingestion did not expedite the metabolic recovery process of these athletes within 48 h post-marathon.