Recent research has been focusing on the multidirectional relationship between the gut microbiome and exercise. The type and intensity of exercise can dictate whether a positive or negative effect is exerted on the gut microbiome.

Endurance exercise can cause an increase in oxidative stress, intestinal permeability, muscle damage, systemic inflammation and immune responses. Regular intense exercise can exert a chronic effect on the immune system that may increase the risk of acute illness in some athletes1

In addition, endurance athletes present with a high prevalence of Upper Respiratory Tract Infections (URTI) during times of high exercise load2. Athletes are more prone to URTI because of the physical and psychological stress of exercise combined with an imbalanced diet, international travel across time zones, disturbed sleep and exposure to environmental extremes3. Their exposure to pathogens may also be increased because of elevated lung ventilation during exercise, skin abrasions, and exposure to large crowds.

Research has shown that adaptations can take place in the body to counter the demands of intensive exercise. The gut microbiome is thought to be an essential part of this adaptive process.

Since the gut microbiome can be modulated either positively or negatively through diet and lifestyle, extra focus needs to be paid to maintaining a diverse gut microbiome. Just as the quality of soil can influence the growth of plants, the diversity of bacteria in the gut microbiome will affect how it functions.

Gut Microbiome
Table 1. Multidirectional effects of Gut Microbiome and Health with relevance to athletes4

On the other hand, exercise is one of the factors that can influence the gut microbiome, in addition to diet, antibiotics, health and disease.

The gut microbiome – an overview

The gut microbiome hosts trillions of bacteria which are classed into types (phyla). Bacteria in the gut falls into two main types, Firmicutes and Bacteroidetes with lower numbers of a third, Actinobacteria. Although each individual gut microbiome is unique, the ratio of phyla is similar amongst individuals. Within each phyla, there are many different classes, families, genera, and species of bacteria and it is this diversity that is associated with a healthier status. Simplistically an abundance of the genera and species bifidobacteria (phyla Actinobacteria) and Prevotella (phyla Bacteroidetes) within the microbiome are seen as beneficial5. These bacterial species selectively ferment dietary fibre and so are usually abundant in the gut microbiome of those who eat a plant-based diet5.

The types of bacteria in the gut microbiome are influenced not only by exercise and diet but by a variety of factors, including age, gender, genetics, lifestyle, medication including use of antibiotics, and disease.

How does the gut microbiome affect health?

The gut microbiome influences human health and immune function, in part through the fermentation of indigestible food components in the large intestine. The gut microbiome and derived metabolites including short-chain fatty acids (SCFAs) have been shown to influence gut function, energy utilisation, cognitive function and immune function (both within the gut and systematically)6.

Effects of intensity and type of exercise on the gut microbiome

The intensity and duration of exercise will affect the gut microbiome. Studies indicate that athletes have a gut microbiome which differs not only from non-athlete controls but also among athletes from different disciplines.

An observational study comparing the faecal bacterial profile of elite male rugby players with non-athlete healthy subjects showed that athletes had lower levels of Bacteroidetes and greater amounts of Firmicutes than controls. This gut microbiome composition may also be associated with their diet, which is high in protein, and low in fibre and is seen as less favourable for health7.

In contrast, another study in amateur and professional cyclists showed that an abundance of beneficial bacteria, Prevotella was significantly correlated with time reported exercising during an average week. In this study, an increased abundance of Prevotella correlated to several amino acid and carbohydrate metabolism pathways, including branched-chain amino acid metabolism7. As mentioned earlier, increased abundance of Prevotella can be associated with eating a plant-based diet6, the study in cyclists is an example that one can modulate the same genus of bacteria not only by diet but also by exercise.

The adaptive responsive of the gut microbiome to endurance exercise has also been demonstrated in a study of marathon runners. The runners were found to have greater numbers of bacteria called Veillonella, which feeds on lactic acid, a compound produced in the muscles during exercise; in turn, the bacteria produce a compound called propionate, which can boost athletic performance8.

The gut microbiome appears to adapt differently to the type and amount of exercise undertaken and the diets of the athletes. Endurance exercise such as cycling, swimming or running, seems to modulate the gut microbiome positively.

The role of the gut microbiome in adaptations to exercise

To some extent, regular exercise and training enables individuals to perform at the height of their abilities and recover after endurance exercise. The physiological and biochemical demands of endurance exercise elicit both muscle-based and systemic responses. The main adaptations to endurance exercise include an improvement of mechanical, metabolic, neuromuscular and contractile function in muscles, a rebalance of electrolytes, a decrease in glycogen storage and an increase in mitochondrial biogenesis in muscle tissue9.

A demonstration of the effect that gut microbiome modulation could have on respiratory issues in individuals with asthma was shown in a study at Nottingham Trent University. Research showed that incidences of hyperpnoea induced bronchoconstriction (HIB) was reduced after administration of prebiotics3.

Interestingly, the capacity for exercise performance appears to be influenced by the gut microbiome, which plays an important role in the production, storage, and expenditure of energy obtained from the diet as well as in inflammation, redox reactions and hydration status.

Studies have shown the gut microbiome can also influence host behaviour via the gut-brain axis, for example by contributing to stress response which may help cope with the demands of competitive sport10. As more athletes suffer from psychological and gastrointestinal conditions, these could be linked to the gut microbiome status and mitigated by dietary adjustments.

Effects of an athlete’s diet on the gut microbiome

Nutritional choices also impact both performance and adaptations to endurance exercise. Generally, the diets typically eaten by athletes are not beneficial to the gut microbiome, as they are high in simple sugars, protein and low in fibre6.

A diet high in protein will mitigate the effects of muscle damage but protein degradation can release toxic metabolites such as ammonia, phenols, p-cresol, certain amines and hydrogen sulphide which affect the gut barrier by increasing intestinal permeability, inflammation and bacterial translocation9. A diet high in fibre may improve gut barrier function through the fermentation of bifidobacteria. Associated metabolites such as butyrate have been shown to help reduce gut permeability and therefore bacterial translocation and inflammation. Studies show that gut bacteria that ferment fibre modulates excitatory and inhibitory neurotransmitters (such as serotonin, GABA and dopamine) in response to physical and emotional stress10, 11. However, athletes, like most of the UK population, fall short of their fibre intake which includes the fermentable (prebiotic) fibre that could outweigh the negative effects of protein on the gut microbiome.

Modifying the gut microbiome through diet

The modulation of the gut microbiome and its fermentation capacity may provide the scientific basis for designing diets aimed at improving performance. This is through enhancing carbohydrate fermentation during exercise and limiting those that produce toxic metabolites from protein degradation. Modifying an athlete’s diet to positively impact the activities of their gut microbiome may also benefit sport performance.

Within the energy restrictions which an athlete may face, it is important to include the recommended daily intake of 30g of fibre, which should include 5g of fermentable (prebiotic) fibre. A diet rich in fruit and vegetables will provide fibre and antioxidants which, in addition to quenching oxidative stress, can have a prebiotic effect.

Studies show that the consumption of polyphenol extracts, such as cocoa and blueberries, modulates the gut microbiome toward a more “health-promoting profile” by increasing the relative abundance of bifidobacteria and lactobacilli12.

Although exercise is shown to have a positive effect on the gut microbiome, this combined with eating the recommended amount of fibre is shown to have the greatest effect. If this is not possible through diet alone then a prebiotic fibre supplement such as Bimuno® should be considered.

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Informed Sport is a quality assurance programme for sports nutrition products. The programme certifies that all nutritional supplements and/or ingredients that bear the Informed Sport logo have been through a rigorous certification process that every batch produced is tested for banned substances by LGC’s world-class sports anti-doping laboratory. You can find approved products and their batch numbers here.

Look for the Informed Sport logo on pack to ensure the products you are purchasing are Informed Sport certified. All products purchased via are guaranteed to be Informed Sport certified.

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Discover more through this webinar

We recently sponsored a webinar featuring Dr. Neil Williams and Dr. Jamie Pugh on the topic of the gut microbiome in athletes.


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