The following blog was written by Maisie Johnson, a third year Food Science and Human Nutrition BSc student joining Clasado Biosciences for hands-on work experience. Maisie is currently working towards graduating as an Associate Nutritionist (ANutr) at Northumbria University, and is eager to further her knowledge by undertaking a Dietetics MSc at Teesside University.

The human gut microbiome is comprised of trillions of microorganisms1, including bacteria, viruses, and fungi. Generally, greater microbial diversity in the gut microbiota is associated with a healthier gut. Overall, the gut microbiome contains five dominant phyla, notably Bacteroidetes and Firmicutes, and thousands of different species1,2. These distinct microorganisms found in the gut microbiome significantly impact metabolic pathways and other physiological systems and mechanisms of the body. This includes key areas such as gut development, the immune system, digestion, cognition and nutrient absorption2. Gut health is becoming increasingly more important as interest around the subject grows and the relationship between the gut microbiome and other parts of the body becomes clearer. Both non–modifiable factors, such as genetics, as well as modifiable factors such as diet and physical activity levels (specifically endurance exercise), have the potential to influence the gut microbiome1,3.

Endurance exercise is defined as “cardiovascular exercise – such as running, cross country skiing, aerobic exercise, or swimming – that is performed for an extended period of time”2. Many sports have an element of endurance training - even if they are not solely an endurance sport. Therefore, the majority of athletes will regularly undergo endurance exercise in some form or another. Throughout this article, the apparent bidirectional association between endurance exercise and the gut microbiome composition will be explored further.

What is the connection between endurance exercise and the gut microbiome?

The impact of endurance exercises on the gut microbiome is not yet fully understood, more studies and interventions are needed to completely comprehend the relationship between the two. There is emerging evidence which suggests that endurance exercise might impact the overall composition of the gut microbiome3. A great research example is Mach et al., (2017) which reported an increase in Prevotella, a genus of gram-negative bacteria, amongst rugby players in comparison to non-healthy individuals2. Similarly, Petersen et al. (2017) reported that cyclists who trained more than 11 hours per week were also found to have a greater abundance of Prevotella and lower levels of Bacteroides spp. than those who trained less often4. These two examples alone show that there might be a correlation between endurance exercise and the composition of the gut microbiome. There is significantly rising interest surrounding the extent to which someone’s gut health may impact their endurance performance. Running is a classic example of where the status of someone’s gut microbiome composition could be a major factor in their physical performance.

Rugby

It is widely known that endurance exercises, such as running, have a great impact on intestinal permeability - swimming and cycling are two other endurance sports which can contribute to this2,5. The concept of a ‘leaky gut’, also known as intestinal permeability, is common in runners – especially those with a greater mileage5. When someone undertakes some form of endurance exercise they are exposing their bodies to intense physiological stressors. In turn, this can disrupt the typical functions and processes within the human body, causing an increase in intestinal permeability2. On the other hand, there is evidence to suggest that regular physical activity does correlate with an increase in short–chain fatty acid (SCFAs) production within human faeces. The increase in SCFAs may enhance the integrity of the intestinal barrier as they provide fuel for the proliferation of enterocytes. This mechanism reduces the likelihood of a leaky gut and could lead to an improved sport and exercise performance3.

Sedentary vs Physically Active Individuals

It is plausible that the gut microbiome composition of a physically active individual holds greater diversity than that of a sedentary individual that participates in less exercise or sport3. In comparison to sedentary individuals, those who are more physically active typically display a wider variation of health–associated microbial genera, such as Prevotella and Veillonella, and comprise a greater faecal microbial diversity3. Despite the need for further research, the beneficial impacts of physical activity on the gut microbiome can be supported by several studies and interventions2,3,4,6,7. For example, the accumulating literature from these studies has demonstrated that the microbiome of athletes and physically active individuals comprises “distinct microbial compositions defined by elevated abundances of Veillonellaceae, Bacteroides, Prevotella, Methanobrevibacter or Akkermansia”7.

Another recent study involving elite rugby players found a significantly higher proportion of Akkermansia in the latter compared to in sedentary individuals2 – supporting the findings of the current literature. Thus, there is a clear association between exercise and changes in the composition of the gut microbiome, supporting the idea that physically active individuals - in comparison to sedentary individuals - hold a greater microbial diversity. 

What is the connection between diet and gut microbiota?

The changes in gut microbiota composition between physically active and sedentary individuals are not solely down to their active lifestyle but could in fact be related to their dietary patterns too2,3. Particular dietary compounds, such as fibre, are considered important influences on gut microbiota composition. Typically, active individuals, in comparison to sedentary individuals, consume a more balanced diet which has greater focus on the nutritional content and energy density of foods and beverages2,3. Thus, dietary patterns, along with numerous other factors such as training times and intensity, cannot be ignored when discussing gut health, specifically the composition of the gut microbiome and exercise performance3.

Continuing the upward momentum of studies in this field, it is vital that further research is undertaken surrounding the impact of the gut microbiota on an individual’s exercise performance as there is not yet enough evidence to provide a definitive answer on this bidirectional relationship. Alongside this, many athletes and physically active individuals regularly report symptoms of intestinal permeability, leading to digestive discomfort and pain whilst they are performing endurance exercises, such as running. Further research into the causations of intestinal permeability and its management strategies should be carried out in the near future. Overall, research of the gut microbiota needs greater attention. The interest from the public surrounding gut health is increasing at a rapid pace, and as individuals get more engaged with physical health, the importance of the gut microbiome is becoming a key focal point for many, including performance athletes.

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