By guest blogger Accredited Sports Dietitian, Andrew Hall.


Probiotic supplementation is gaining more traction in sporting circles due to suggested benefits on health, immune strength and exercise performance. Probiotics are classified as live microorganisms that provide a health benefit to the individual when administered in adequate amounts (6). These microorganisms exhibit strain-specific differences in their ability to colonise the gastrointestinal (GI) tract, or “Microbiome” (2). The Microbiome, which some are suggesting essentially be classed as an “organ”, is continuing to be the focus of many research groups due to rapid developments in technologies that allow evaluation of bacterial species and strains that normally inhabit the gut (4). The gut and the microbiota are important organs for athletic performance, as they are responsible for the delivery of water, nutrients and hormones during exercise (1). Microbes in the distal gut may contribute to biosynthesis of vitamins and essential amino acids, as well as generation of important metabolic byproducts from dietary components left undigested by the small intestine. Short chain fatty acid (SCFA) byproducts such as butyrate, propionate, and acetate act as a major energy source for intestinal epithelial cells and may therefore strengthen the mucosal barrier (5). Ideally, an increased consumption of complex plant polysaccharides should be promoted to help maintain gut microbiota diversity and function, but this isn’t always possible with the athletic population (more on this soon). For this reason, it is worthwhile Sports Dietitians ensure that microbiota health (and probiotics) be considered in screening and nutrition therapy.


Probiotics are available commercially in capsule form, as a powder or in selected dairy products such as fermented milk or yoghurt. The most commonly used species of probiotics include Lactobacillus and Bifidobacterium, but the yeast Saccharomyces boulardii and some E. coli and Bacillus species are also used. Lactic acid bacteria, including Lactobacillus species, which have been used for preservation of food by fermentation for thousands of years, can act as agents for food fermentation and, in addition, potentially convey health benefits. Strictly speaking, however, the term “probiotic” should be reserved for live microbes that have been shown in controlled human studies to yield a health benefit (6).


When it comes to supporting a healthy microbiome, an athletes lifestyle/training program certainly challenges the balance. Here are just some of the reasons why athletes might look to supplement with probiotics.


Athletes with extensive training loads subsequently have large caloric intake demands. Due to time-critical recovery requirements (restoring muscle glycogen, meeting protein and healthy fat needs), high fibre diets can often be nudged down the priority list. This is particularly pertinent with athletes training twice per day or for seriously long hours (cyclist training rides etc). In this instance, high fibre foods are not welcomed/appropriate during this large proportion of their waking day. Therefore, the lack of complex carbohydrates in elite athletes’ diets may negatively affect the gut microbiota composition and function in the long run (1). As we know, diets rich in whole grains and wheat bran are linked to an increases in gut Bifidobacteria and Lactobacilli. Other non-digestible carbohydrates, such as resistant starch and whole grain barley, appear to also increase the abundance of Ruminococcus, E. rectale, and Roseburia. So, athletes can be at risk for dysbiosis in this respect (5).


Symptoms associated with GI distress (e.g., cramping, diarrhoea, nausea, and abdominal pain) are estimated to occur in 25%–90% of endurance athletes, and are often cited as reasons for non-completion (7). Prolonged physical exertion, particularly running exercise, appears to impact intestinal epithelial integrity. The epithelial lining along the GI tract plays a significant protective role in preventing the penetration of enteric pathogenic microorganisms into portal and systemic circulation. Alterations to intestinal motility and mechanical trauma (i.e., repetitive jarring associated with running) can further promote intestinal mucosa and epithelial damage and/or dysfunction (3). These acute changes in tight junction permeability may lead to a greater prevalence of systemic lipopolysaccharides (LPS) escaping. As a result, LPS from intestinal bacteria may provoke immune responses and endotoxin-associated symptoms characteristic of GI complaints often experienced in runners (7).


Exercise-induced stress modifies stress and catabolic hormones, cytokines and gut microbial molecules, which can result in GI disturbances, anxiety, depression, and underperformance (1). Research suggests that fluctuations in athletes’ mood and GI function during times of intense physical stress may reflect the underlying interaction between the gut microbiota and gut-brain axis. It has been demonstrated that bacteria have the capacity to generate neuromodulators as well as neurotransmitters, including GABA, serotonin and noradrenalin, dopamine, and acetylcholine (8). This impact can be demonstrated when accentuating the neurotransmitter serotonin. Low serotonin in the brain may cause mood disorders and depression as well as changes in gut transit, blood pressure, cardiac function and platelet aggregation (1). Approximately 95% of the body’s serotonin is produced in the enterochromaffin cells of the intestines, as it impacts enteric motor and sensory functions such as visceral pain perception, illustrating the gut-brain connection potential (1).


There is now a reasonable body of evidence that shows probiotics may reduce the risk of respiratory and GI illness during stressful periods of training and competition (particularly for individuals undertaking endurance training, and those more susceptible to GI symptoms) (2,7). Additionally, supplementation is suggested to improve stress-induced symptoms such as depression, mood disturbance and other digestive issues such as inflammation (1). The clinical benefits of probiotics are most likely mediated by changes in gut microbiota, SCFA metabolites, and enhanced mucosal barrier integrity in the GI and respiratory tracts. However, before commencing probiotic supplementation, there are a few practical aspects worth considering.  Pyne Et al. suggest medical and dietary review of individual athletes, exposure to probiotics well before competition to establish individual tolerance and possible side effects and daily monitoring during periods of intensive training and competition. Probiotic supplementation should be trialled during the preseason phase, or otherwise the early- to mid-stages of a competitive season, so the athlete is familiar with taking the supplements (2). Probiotic supplementation is highly variable depending on the strain and microbiota composition and thus there have not yet been specific established dosages nor strains in athletes (1). More research is required to clarify issues of strains, dose–response, mechanisms and best practice models for probiotic implementation in the sporting community (2).

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1.      Clark, A., & Mach, N. (2016). Exercise-induced stress behavior, gut-microbiota-brain axis and diet: a systematic review for athletes. Journal of the International Society of Sports Nutrition13(1), 43.

2.      Pyne, D. B., West, N. P., Cox, A. J., & Cripps, A. W. (2015). Probiotics supplementation for athletes–clinical and physiological effects. European journal of sport science15(1), 63-72.

3.      Gill, S. K., Teixeira, A., Rama, L., Rosado, F., Hankey, J., Scheer, V., … & Costa, R. J. (2015). Circulatory endotoxin concentration and cytokine profile in response to exertional-heat stress during a multi-stage ultra-marathon competition. Exercise immunology review21.

4.      Iqbal, S., & Quigley, E. M. (2016). Progress in our understanding of the gut microbiome: implications for the clinician. Current gastroenterology reports18(9), 49.

5.      Singh, R. K., Chang, H. W., Yan, D., Lee, K. M., Ucmak, D., Wong, K., … & Bhutani, T. (2017). Influence of diet on the gut microbiome and implications for human health. Journal of Translational Medicine15(1), 73.

6.      World Gastroenterology Organisation Global Guidelines (February 2017) Probiotics and prebiotics. WGO Link

7.      Roberts, J. D., Suckling, C. A., Peedle, G. Y., Murphy, J. A., Dawkins, T. G., & Roberts, M. G. (2016). An Exploratory Investigation of Endotoxin Levels in Novice Long Distance Triathletes, and the Effects of a Multi-Strain Probiotic/Prebiotic, Antioxidant Intervention. Nutrients8(11), 733.

8.      McKean, J., Naug, H., Nikbakht, E., Amiet, B., & Colson, N. (2016). Probiotics and Subclinical Psychological Symptoms in Healthy Participants: A Systematic Review and Meta-Analysis. The Journal of Alternative and Complementary Medicine.


Originally published

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