Recent research has been focusing on the multidirectional relationship between the gut microbiome and exercise. The type and intensity of the 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 athletes.1 

In addition, endurance athletes present with a high prevalence of Upper Respiratory Tract Infections (URTI)2. 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 diversity in gut bacteria. Just as the quality of soil can influence the growth of plants, the diversity of gut bacteria in the microbiome will affect how it functions.

Multidirectional effects of Gut Microbiome and Health with relevance to athletes - Bimuno
Table 1. Multidirectional effects of Gut Microbiome and Health with relevance to athletes4 5

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 sit under two main types, Firmicutes and Bacteroidetes with lower numbers of Actinobacteria. Although each individual gut microbiome is unique, the ratio of phyla is similar amongst individuals. Within each phyla, there are many different strains of bacteria and it is this diversity that is associated with a healthier status. Simplistically an abundance of the species bifidobacteria (phyla Actinobacteria) and Prevotella (phyla Bacteroidetes) within the microbiome are seen as beneficial5. These species of bacteria selectively ferment dietary fibre and so are usually abundant in the gut microbiomes of those who eat a plant-based diet7.

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, antibiotics, health 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 have been shown to influence gut function, energy utilisation, cognitive function and immune function (both within the gut and systematically)8.

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 gut microbiome enterotypes which differ not only from non-athlete controls but also between athletes from other disciplines.

An observational study comparing the faecal bacterial profile of male elite 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 enterotype may also be associated with their diet, high in protein, and low in fibre and is not seen as a positive for health9.

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 metabolism10. As mentioned earlier, increased abundance of Prevotella can be also associated with eating a plant-based diet7, so 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 recent study of Marathon runners. The runners were found to have greater numbers of a bacteria which consumed lactic acid, which can cause muscle stiffness, into propionate which can boost performance.11

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, the body has an ability to adapt through regular exercise training which 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 functions in muscle, a rebalance of electrolytes, a decrease in glycogen storage and an increase in mitochondrial biogenesis in muscle tissue12.

A demonstration on the effect that gut microbiome modulation could have on respiratory issues in athletes was shown in a study at Nottingham Trent University. Research in athletes showed that incidences of hyperpnoea induced bronchoconstriction (HIB) was reduced after administration of prebiotics13.

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 that the gut microbiome can also influence host behaviour via the gut-brain axis, for example by contributing to stress response which might help cope with the demands of competitive sport15. 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 fibre.7 14

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 translocation15. A diet high in fibre may improve gut barrier function through the fermentation of bifidobacteria, and associated metabolites such as butyrate have been shown to help reduce gut permeability and therefore bacterial translocation and inflammation. Studies show that gut microbiota that ferments fibre modulates excitatory and inhibitory neurotransmitters (such as serotonin, GABA and dopamine) in response to physical and emotional stress8. However, athletes, common to 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

With this in mind, the modulation of the gut microbiome and its fermentation capacity may provide the scientific basis for designing diets aimed at improving performance by enhancing carbohydrate fermentation during exercise and limiting those that produce toxic metabolites from protein degradation. Modifying an athlete’s diet in a way in which they positively impact the activities of their gut microbiome may also benefit sport performance.

Within the energy restrictions which may be imposed on an athlete, 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 red wine, cocoa, and blueberry, modulates the gut microbiome toward a more “health-promoting profile” by increasing the relative abundance of bifidobacteria and lactobacilli.16

In summary, 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 high fibre food supplement such as Bimuno® should be considered.

In addition, Bimuno TRAVELAID contains gelatin which is important for athletes as it plays a role in collagen synthesis which is important for injury prevention and tissue repair. Research has demonstrated that 5g of gelatin consumed 30 minutes before exercise increases levels of amino acids’, glycine, proline, hydroxyproline, and hydroxylysine. A serving of Bimuno Travelaid provides 5.8g of gelatin.17

Bimuno is certified with Informed Sport

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 check approved products and their batch numbers here.

At present, only Bimuno products that are purchased via are guaranteed to have been certified by Informed Sport. All batch tested products will have the Informed Sport logo on the pack. Informed Sport certified Bimuno products will be available in retail stores from late 2019.

WEBINAR: The Gut Microbiome in Athletes: The role of Prebiotics

The  Gut Microbiome in Athletes: The role of Prebiotics

Our latest blog posts

For Healthcare Professionals

View all

More for Healthcare Professionals

Our Products


This section is an information and educational resource for healthcare professionals. It is not intended for consumers. If you wish to purchase Bimuno please click here