probiotics for athletes

INTRO

Probiotic supplementation is gaining more traction in sporting circles due to suggested benefits on health, immune strength, and exercise performance. Probiotics are defined 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, often referred to as an “organ”, is the focus of many research groups dueto rapid developments in technologies that allow evaluation of bacterial 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 especially 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.

A GOOD KIND OF STRAIN

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 Lactobacillusand Bifidobacterium, but the yeast Saccharomyces boulardii and some E. coli and Bacillusspecies are also used. Lactic acid bacteria, including the Lactobacillusspecies have both social and medical benefits; they have been used for preservation of food by fermentation for thousands of years, can act as agents for food fermentation, and potentially provide 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).

HEIGHTENED CHALLENGES FOR AN ATHLETES MICROBIOME

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

REDUCED CONSUMPTION OF NON-DIGESTIBLE CARBOHYDRATES (LESS FIBRE) 

Athletes with extensive training loads 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 extended hours (cyclist training rides etc). In this instance, high fibre foods are not welcomed/appropriate during exercise, which equates to a large proportion of the athletes 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 increase in gut Bifidobacteriaand Lactobacilli. Other non-digestible carbohydrates, such as resistant starch and whole grain barley, appear to also increase abundance of Ruminococcus, E. rectale, and Roseburia. As a result, fibre-deficient athletes are at risk for dysbiosis in this respect (5). 

GI ISCHEMIA, PERMEABILITY & IMMUNE FUNCTION

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 endurance running, appears to impact intestinal epithelial integrity. The epithelial lining along the GI tract plays a significant 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 mucosal damage and/or dysfunction (3).These acute changes in tight junction permeability may lead to a greater prevalence of systemic lipopolysaccharides (LPS) traversing the GI wall and entering the systemic circulation. As a result, LPS from intestinal bacteria may provoke immune responses and endotoxin-associated symptoms characteristic of GI complaints often experienced in runners (7). Furthermore, recent interest in the use of probiotics has focused on preventing respiratory illness, particularly the common cold. From an immunological perspective, the gut plays a primary role in mediating defence against infection and regulating mucosal homeostasis (2).

STRESS, FATIGUE & MOOD DISTURBANCES

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 concurrent fluctuations in athletes’ mood and GI function during times of intense physical stress may cause the underlying interaction between neuropsychological stress and gut microbiota. Bacteria have the capacity to impact mood, due to the generation of neurotransmitters including GABA, serotonin and noradrenalin, dopamine, and acetylcholine (8). This impact can be demonstrated when accentuating the neurotransmitter serotonin, as low serotonin in the brain is associated with mood disorders and depression. Additionally, low serotonin influence 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 (1).

POSSIBLE MODES OF ACTION & PRACTICAL APPLICATION

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 and mood disturbance (1). Probiotics change gut microbiota, therefore providing clinical benefits via SCFA metabolitesand 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).Due to the high variability in species and strain composition of commercial probiotic supplements, optimal dosages and strains have not yet been established for 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).

REFERENCES

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 Nutrition, 13(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 science, 15(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 review, 21.

4.     Iqbal, S., & Quigley, E. M. (2016). Progress in our understanding of the gut microbiome: implications for the clinician. Current gastroenterology reports, 18(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 Medicine, 15(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. Nutrients, 8(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.