In addition to extensive training, athletes may seek optimum physical and mental wellness through diet, meditation, sleep aids, and numerous supplements. In the past few decades, the microbiome has become another area of intense interest in this regard. This article looks at the role of the microbiota as well as the potential for probiotics to enhance health, recovery, and performance in athletes. 

Gut microbiota in athletes

Athletes possess distinct microbiota influenced by exercise and diet. Based on animal and/or human studies, research shows that exercise may play a crucial role in enriching microbiota diversity, altering the Bacteroidetes-Firmicutes ratio, and enhancing mucosal immunity and gut barrier functions. Elite athletes show other microbiota differences from their sedentary counterparts. In one example, an increase in Veillonella atypica abundance was linked to improvement in endurance performance (due to lactate conversion to propionate). Nevertheless, extended, intense exercise can harm intestinal function by redirecting blood flow (splanchnic hypoperfusion) from the intestines to active muscles, potentially causing mucosal damage, enterocyte injury, and increased gut permeability, particularly in endurance sports. 

Researching the human gut microbiota in athletes poses challenges in isolating the impacts of exercise and diet due to their connections, including changes in dietary habits associated with physical activity (e.g., heightened protein intake in resistance-trained athletes or increased carbohydrate consumption in endurance athletes, alongside overall increased energy and nutrient intake). For example, in athletes, protein intake is a robust modulator of the microbiota while high complex carbohydrate intake is associated with richer microbial diversity with an increased abundance of Prevotella. 

Nonetheless, many studies have focused on the effect of altering the gut microbiota with probiotic supplementation in athletes. Probiotics as functional modulators of the microbiome may possibly promote health, exercise adaptation, and performance in athletes. 

Intense physical exercise can negatively impact various systems in the body that are linked to gut microbiota. Many of these common adverse effects may potentially be alleviated with modification via probiotics. Let’s look at the evidence regarding:

Intestinal permeability

Extreme physical exertion strains the gastrointestinal system, heightening the risk of various symptoms such as abdominal discomfort, heartburn, nausea, vomiting, diarrhea, and increased gut permeability potentially leading to systemic toxemia. 

Probiotic supplementation may support the gut epithelial barrier, which is crucial for maintaining epithelial integrity and protecting the host from environmental threats; potential mechanisms include enhancing tight junction signaling, promoting mucus secretion, and preventing endotoxemia, although further research is needed to fully understand these processes and their implications for gastrointestinal health in athletes undergoing strenuous exercise.

Certain multi-strain probiotics  (lactobacilli and bifidobacteria) combined with prebiotics have demonstrated value in enhancing gut-barrier function among athletes.

Immune response

The mucosal lining of the GI tract serves as the primary barrier against pathogens and interacts closely with the host immune system. While low to moderate exercise can improve immune function, high-intensity exercise can lead to immunosuppression for as long as several days. These effects include reduced counts and functionality of immune cells like natural killer (NK) cells and T lymphocytes, with alterations in cytokine levels and gene expression. 

As a result, a compromised immune system increases susceptibility to illness in the athlete which can impact training and performance. Indeed, an athlete is more prone to upper respiratory tract infections (URTIs) during periods of intense training and competition. 

Probiotics may regulate immune response, enhance macrophage activity, modulate gene expression, interact with Toll-like receptors, and influence various aspects of immune function. According to an International Society of Sports Nutrition Position Paper, one well-known mechanism that probiotic bacteria enlist is by adhering to the intestinal mucosa resulting in competitive exclusion “involving competition for receptor sites, secretion of antimicrobial substances, and induction of mucin alterations, which collectively modulate the immune system, antagonize pathogens, and inhibit the attachment of pathogenic bacteria.“

Many studies have explored the effect of probiotic supplementation on outcomes related to the immune system in athletes. 

The previously mentioned position paper reported that of the 22 studies reviewed to assess the “effect of probiotics on outcomes related to the immune system, 14 reported significant improvements, whereas 8 reported no effects.” 

Moreover, a recent systematic review reported the beneficial effects of both single-strain and multi-species probiotics consumption on the incidence, duration, and/or severity of URTIs in athletes. Alteration of the inflammatory cytokine profile is suggested as a primary mechanism driving the immune-modulating effects of probiotics in athletes.

Inflammation

Probiotics may also serve to reduce inflammation in sore muscles after exercise. This effect may be partially mediated by antioxidant effects manifested by probiotics because certain strains may increase antioxidant levels and neutralize the effects of reactive oxygen species. 

In addition, probiotics may reduce hyperglycemia, a condition linked to oxidative stress. Probiotics can also be a source of  postbiotics, which may contribute to antioxidant and immunomodulatory effects.

Moreover, probiotics produce vitamins (mostly B vitamins), some of which can reduce oxidative stress, though their use in athletes for this outcome is controversial.

A study evaluated the effect of 14 weeks multi-species probiotic supplementation on markers of oxidative stress and inflammation and results showed that supplementation decreased protein oxidation and the chronic inflammatory marker TNF-α.

Bioavailability of nutrients

Probiotics may improve dietary protein absorption and utilization, which is important in strength recovery. The amounts of glycogen (stored energy for muscles) in the liver and muscles may also be increased by probiotics. In addition, probiotics can enhance the absorption of other nutrients such as iron, which when deficient can harm performance. 

Probiotics & sports performance

When intense exercise leads to a “leaky gut,” inflammation, and a compromised immune system, training is interrupted—performance can suffer. Supplementing with probiotics may ameliorate some of the physiological effects. Altering the microbiome may influence various indices of exercise performance and recovery.

A recent systematic review of interventions conducted from 2014 to 2021 looked at the effects of probiotics on different performance aspects (skill, strength, endurance, and recovery) in different sports. Endurance sports with male athletes were most represented. Various metrics were used in the diverse studies including body composition, anaerobic and aerobic capacities, muscle damage, and muscle fatigue tests. Of the 13 studies, 11 reported positive effects (not all significant) of probiotic supplementation on different measurements of sports performance. The authors noted that the heterogeneity of the studies (probiotic benefits are strain-specific) precluded definitive conclusions. 

Another meta-analysis and systematic review found that supplementing with probiotics positively impacts performance, particularly in a trained population where aerobic metabolism is predominant. Results indicated that consuming single-strain probiotics for ≤4 weeks yielded greater benefits than a placebo. 

For a comprehensive list of probiotic studies in an athletic population, refer to Table 3 in the aforementioned position paper. The same paper includes Table 5 entailing approved Canadian probiotics claims for sports performance.

Takeaway

The athlete’s microbiome, particularly its modulation through probiotics, has emerged as a significant area of interest in overall health, recovery, and performance. Athletes exhibit distinct microbiota influenced by their exercise routines and dietary habits, impacting diverse aspects such as gut barrier function, immune response, and inflammation. While intense exercise can strain the gastrointestinal system, leading to symptoms like heightened gut permeability and compromised immunity, probiotic supplementation shows promise in supporting gut health and bolstering immune function. Moreover, probiotics may aid in reducing inflammation, improving nutrient absorption, and enhancing sports performance and recovery. However, further research is needed to fully understand the strain-specific benefits of probiotics and their optimal usage in an athletic context.

*Key references are available in the web version of this article, at WholeFoodsMagazine.com.

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Authorship

The International Probiotics Association (IPA) is a global non-profit organization bringing together, through its membership, the probiotic sector's stakeholders, including but not limited to academia, scientists, healthcare professionals, consumers, industry, and regulators. The IPA's mission is to promote the safe and efficacious use of probiotics worldwide. Holding NGO status before Codex Alimentarius, the IPA is also recognized as the unified "Global Voice of Probiotics" around the world.

Clare Fleishman, MS RDN, bridges the gap between science and health across most platforms: major newspapers, magazines, books (Globesity), workshops, social media, and websites. In 2010, she launched www.ProbioticsNow.com to share the cascade of new discoveries in the microbiome. Always amazed at this "forgotten organ," Fleishman has also created white papers, blogs, videos, and social media for the International Probiotics Association. She recently published Fertility: Why Microbes, Weight & Nutrition Matter.

Edited by IPA Scientific Committee members: 

Dr. Arthur Ouwehand, PhD, Technical Fellow at IFF Finland

Dr. Carolyn Gugger, PhD, RD, Senior Director of Regulatory & Scientific Affairs at Nature's Way