Microbial instability in the gut could hinder the performance of elite endurance athletes

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New research has found that microbial instability in the gut could hinder the performance of elite endurance athletes, and that short-term, high-protein diets are associated with this type of imbalance.

Researchers from across the UK analysed the performance and gut health of a group of well-matched, highly trained endurance runners, to explore the impact of both high-protein and high-carbohydrate diets.

The study found that in those following a high-protein regime, this resulted in a disturbance in the stability of the gut microbiome. This was also accompanied by a 23.3% reduction in time trial performance.

Analysis found a significantly reduced diversity and altered composition of the gut phageome, as well as higher levels of certain types of virals and bacterial compartments. Those participants whose gut microbiome was more stable performed better during time trials.

Gut imbalance impacts different people in different ways, but can manifest itself in acute symptoms such as cramps or nausea. As there is cross-talk between the gut and the brain, authors suggest this could be important.

Those following a high-carbohydrate diet resulted in an improved time trial performance of 6.5%.

Dr Justin Roberts, Associate Professor in Health and Exercise Nutrition at Anglia Ruskin University (ARU) and co-author of the study, said: “These results suggest that athletic performance may be linked with gut microbial stability, where athletes who had more stable microbial communities consistently performed best in each dietary intervention compared to those with a more turbulent gut microbiota.

“While we cannot be certain that the high amount of protein in the body was entirely responsible for the significant drop in time-trial performance, it was found that there were certainly changes to the gut microbiome following a short-term high-protein diet which appeared to be associated with performance.

“These results suggest that consuming a high-protein diet may negatively impact the gut via an altered microbial pattern, while a high-carbohydrate intake, for example containing a variety of grains and vegetables, was associated with greater gut microbial stability.

“The diets were well controlled and carefully balanced and so we think it is unlikely that the protein itself caused a drop in performance. Instead we think it is possible that the changes to the gut microbiome could impact intestinal permeability or nutrient absorbtion, or the messages between the gut and the brain, affecting perceived effort and therefore performance.”

The study was published in the American Society for Microbiology’s journal mSystems and was carried out by researchers from Northumbria University, Anglia Ruskin University (ARU), University of Reading, Newcastle University, University of Kent, University of Hertfordshire and Northwest University in South Africa.


The human gastrointestinal (GI) tract harbors a vast number of microbial cells (1014), which surpasses the number of cells that make up the human body [1]. Although many intestinal microbiota species are beneficial, others are potentially detrimental, or their functions remain unknown. These resident microbes are involved in many metabolic processes, such as the fermentation of undigested carbohydrates into short-chain fatty acids (SCFAs), lipid metabolism, and vitamin synthesis. Intestinal microbiota also stimulates the maturation of the immune system and protects against potentially pathogenic microbes [2]. Further, the microbiota may play a role in cognitive performance and stress tolerance [3,4].

A healthy adult gut is characterized by a high degree of microbial richness (diversity) [5], favoring health-promoting species, and features an intact epithelial barrier, which affects the inflammatory status and nutrient utilization of the host [6]. Genetic and environmental factors, in addition to diet and antibiotic use, have major influences on the gut microbiota composition, starting in early childhood and extending into adulthood [7].

Dysbiosis and the loss of diversity among gut microbiota species have been associated with various immune-regulated pathological conditions and diseases and may, in part, contribute to the risks of developing obesity-related disorders [7,8]. Gut microbiota populations with high degrees of microbial diversity have been associated with various health benefits in adults.

Gut microbes have the potential to exert effects via metabolites, such as SCFAs and neurotransmitters, that can influence mucosal tissues locally or enter the circulation to affect extra-intestinal tissues. Recently, these findings have resulted in the conceptualization of a gut-brain axis (for review see [9]) and a gut-muscle axis (for review see [10]) indicating the existence of bidirectional communications between the gut microbiota and the peripheral tissues of the host.

Exercise has well-known effects on cardiorespiratory fitness, muscle strength, glucose metabolism, the immune system, and mental health [11]. Emerging evidence has indicated a plausible association between physical activity and the gut microbiota composition [12,13,14]. The particular features of gut microbiota compositions found in athletic individuals and the impacts of exercise on the gut microbiota compositions of sedentary populations have begun to be revealed. Intervention studies have supported the beneficial impacts of exercise and physical activity on the gut microbiota [15,16,17]. Furthermore, a growing interest has developed regarding whether the modification of the gut microbiota composition can affect the exercise and training outcomes of the host.

Probiotics are, by definition, “live micro-organisms that, when administered in adequate amounts, confer a health benefit on the host” [18]. Probiotic supplementation may modify the gut microbiota composition, promoting increased microbial diversity and supporting the growth of health-promoting species [19,20,21]. Probiotics may also help restore a disturbed gut microbiota [15] and support a microbiota under stress [22,23]. Although, many probiotics can support a general healthy GI and immune system function, the specific mechanisms underlying probiotic actions, such as the production of bioactive compounds, the inhibition of pathogen adhesion, the improvement of gut barrier function, and immune modulation, may be highly strain-specific, even within a single bacterial species [18].

Thus far, probiotic research has primarily focused on GI function and immune regulation; however, recent studies have targeted new research areas, such as metabolic and cognitive health. The well-established probiotic effects on gut health and immune system function may benefit endurance athletes, who train and perform at high intensities and often encounter physiological challenges associated with GI and immune health during and after a competition.

Therefore, probiotic supplementation may indirectly improve the performance of an athlete by increasing the number of healthy training and competition days and maybe even benefit stamina. The benefits of probiotics for sports performance and training have been recognized, although the number of studies that have examined these issues remains limited. Recently, the International Society of Sports Nutrition (ISSN) provided a position stand on probiotics, concluding that probiotics have strain-specific effects in athletes [24]. In this review, we provide an overview of the current research on the relationships between exercise and gut microbiota and further evaluate the indirect and direct effects of probiotics on physical performance, in animal models and human subjects.

Gut Microbiota and Physical Performance
Exercise has well-known effects on metabolism and the immune system, but the effects of exercise on the gut microbiota have been less well studied. Compared with sedentary subjects, athletes and physically active subjects appear to have greater fecal microbial diversity and more health-associated microbial genera, such as Akkermansia, Veillonella and Prevotella [12,13,14].

However, the results of these observational studies can only confirm associations between training status and microbiota populations, without determining causality. In addition to physical activity patterns, sedentary subjects often differ from physically active subjects in dietary intake patterns [25], and diet has a strong impact on the gut microbiota composition [26].

The association between exercise and the gut microbiota composition appears to be bidirectional. Exercise intervention studies in humans have indicated that regular physical activity modulates the gut microbial composition [15,16,17]. Furthermore, growing evidence from animal studies has also suggested that the gut microbiota plays an important role in the physical performance of the host [27,28,29].

The composition and metabolic activity of gut microbiota may aid in the digestion of dietary compounds and improve energy harvest during exercise, which could provide metabolic benefits for an athlete during high-intensity exercise and recovery. Observational studies have demonstrated that the metabolic activity and pathways associated with amino acid and carbohydrate metabolism are increased among the athlete microbiome compared with those in sedentary subjects [13,14,30].

In the gut, bacteria ferment non-digestible carbohydrates, primarily into SCFAs acetate, propionate and butyrate. Training and regular exercise have been associated with increased fecal SCFA contents in humans [15,30], and specific SCFAs have been associated with improved physical performance in animal studies [14,29].

Most SCFAs are absorbed from the intestinal tract and contribute to the host’s energy metabolism [31]. Butyrate is used primarily by epithelial cells in the colon, as an energy source. Acetate is metabolized in muscle tissue but can also cross the blood-brain barrier. Propionate can be used as a precursor for glucose synthesis in the liver [31]. Additionally, SCFAs improve intestinal barrier integrity, reducing local and systemic inflammation risk. Preclinical studies have strongly suggested that SCFAs may represent key modulators of physical performance.

Notably, the host may not be the only party to benefit from the symbiotic relationship with microbiota during exercise. A recent study suggested that lactate, produced by the host skeletal muscles during anaerobic exercise, enters the gut lumen through circulation, providing a selective advantage for lactate-utilizing species that reside in the colon [14]. The results from this seminal work imply that during high-intensity exercise, the host provides fuel, in the form of lactate, for specific bacteria, which, in turn, produce metabolites, such as propionate, that benefit the exercising host. Current research on the interactions between the gut microbiota and physical performance is reviewed below and summarized in Figure 1.

Figure 1
Interactions between gut microbiota and exercise.

reference link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7599951/


Original Research: Open access.
Gut Microbial Stability is Associated with Greater Endurance Performance in Athletes Undertaking Dietary Periodization” by Justin Roberts et al. mSystems

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