Marathon Runners and Probiotics

    Portrait of happy young fitness woman running with earphones

    Probiotics Help Marathoners Go the Distance

    Like most exercise, running is good for your microbes. However, a marathon (26.219 miles) can be an extreme challenge leading to gut dysbiosis, immunosuppression and respiratory problems. Clearly, care of a healthy gut microbiome is vital for an athlete’s health, training and performance. New research shows that probiotics may help runners reach the finish line.

    Quick review: Exercise and the microbiome

    Hundreds of microbial species in the human body are fairly stable. Exercise can change the microbiome, usually in a beneficial manner.

    Compared to sedentary people, athletes have increased gut microbial diversity, a generally accepted positive attribute.

    Athletes’ gut microbiota also had a higher abundance of short-chain fatty acids (SCFA) metabolic pathways, an indicator of health.

    Specific microbes stand out. For example, a 2019 study reported that the genus Veillonella was enriched in the gut microbiome of marathon runners when compared to non-runners. In mice, the species Veillonella atypica increased endurance, reduced inflammatory cytokines, and converted lactate to acetate/propionate.

    Studies of exercise and the gut microbiome are summarized in this table included in an excellent review titled The Potential Impact of Probiotics on the Gut Microbiome of Athletes.

    Extreme exercise or overtraining as in a marathon may have different effects. The aforementioned paper published in the journal Nutrients in 2019 explains the risks and possible negative effects. Oxidative stress, increased gut permeability, immunosuppression, susceptibility to infections and even depression can be triggered by extreme exercise such as a marathon.

    Fortuitously, in a recent systematic review, probiotic supplementation was observed to lead to positive effects for several outcomes including gastrointestinal symptoms, immunologic markers and respiratory tract infection, in both athletes and non-athletes.

    Oxidative stress

    Normal metabolism creates free radicals. If antioxidants fail to neutralize them, an imbalance called oxidative stress ensues which causes inflammation and tissue damage. Intense physical exercise can lead to oxidative stress.

    Probiotics may add to the antioxidant arsenal. While there are many, the following species are documented in that capacity: Lactobacillus (L.) delbrueckii ssp. bulgaricus, L. delbrueckii ssp. lactis, L. acidophilus, L. casei as well as Bifidobacterium animalis. All of them produce organic acids (acetate and lactate) that in turn are converted into butyrate, a short chain fatty acid beneficial to the immune system.

    In a small clinical trial, two probiotic strains given during a four-week time frame of intense training successfully lowered the oxidative stress caused by the intense exercise.

    Leaky gut effects

    Endurance athletes often suffer from what is termed “leaky gut,” a condition where the intestinal lining becomes more permeable, leading to numerous well-documented problems:

    • Infections including cold and flu
    • Increased inflammation
    • Diarrhea, nausea and vomiting
    • Slowed tissue repair
    • Suboptimal performance

    Probiotics may be useful in leaky gut

    Researchers recently asked whether probiotics may alleviate some of that distress. Four weeks of probiotic supplementation reduces GI symptoms during a marathon race appeared in the European Journal of Applied Physiology in 2019. The 24 runners were randomly assigned to a probiotic or a placebo group. The probiotic group received daily supplements of strains of Lactobacillus acidophilus, Bifidobacterium bifidum, and Bifidobacterium animalis subsp. lactis for 28 days before a marathon race event. The results were promising.

    • In the probiotic group, gastrointestinal (GI) symptoms were lower during the 3rd and 4th weeks compared to the first two weeks. The placebo group saw no change.
    • Also, GI symptom severity during the final third of race was lower in probiotic group compared to the placebo group.
    • No differences in finish times were observed between the two groups.

    The authors concluded:

    “Probiotics supplementation was associated with a lower incidence and severity of GI symptoms in marathon runners, although the exact mechanisms are yet to be elucidated. Reducing GI symptoms during marathon running may help maintain running pace during the latter stages of racing.”


    Intense training can lead to immunosuppression. The normal protective tools of the upper airways, including immune cells, antimicrobial peptides, immunoglobulins, and cytokines are affected, leading to a breakdown in homeostasis.

    Indeed upper respiratory tract infections, both in training and races, are more common in these runners. In addition to immune changes, inflammatory events in the airways may also be responsible by such alterations.

    One example of a probiotic connection, some lactobacilli may regulate the mucosal and systemic immune systems. Ingestion of certain strains of Lactobacillus rhamnosus and Lactobacillus casei had protective effects on the incidence of respiratory and gastrointestinal tract symptoms during the training period and two weeks after a marathon. Moreover, the frequency, duration, and severity of these symptoms were decreased in lactobacilli-supplemented individuals.

    One recent study from Mauro Vaisberg and colleagues in Brazil led to promising results. Forty-two male marathon runners ingested a fermented milk containing 40 billion CFU of L. casei Shirota/day (n=20) or placebo (n=22) during 30 days pre-marathon.

    Results in the probiotic-treated group:

    • Salivary levels of both SIgA and antimicrobial peptides maintained.
    • Nasal IL-10 levels, a classic anti-inflammatory cytokine, increased.
    • Nasal levels of proinflammatory cytokines were reduced.
    • Nasal mucosal neutrophil infiltration decreased, demonstrating an anti-inflammatory effect.

    The probiotic was able to modulate both immunological and inflammatory responses in the blood and also in the upper airway mucosa of runners after a marathon.


    The immune system has a tough job: weeding out pathogens lurking in a thicket of commensal bacteria. It uses a highly complex system of molecules and cells (pattern recognition receptor (PRR) families expressed in immune cells.)

    These bacteria in our microbiota have “skin in the game”: They produce antimicrobials to ward off invaders. There are several types: bacteriocins, and other compounds including hydrogen peroxide, lactic acid, and acetic acid. Further, some of the members of our microbiota are able to induce a strengthened mucosal barrier function.

    A few quick examples:

    Studies using probiotics on physically active and athlete cohorts are summarized in this excellent table.

    Mental Health

    It is said that the mind wins the race.

    Yet depression is common in athletes. Indeed, preliminary studies show that certain probiotics may alleviate depression in athletes by successfully reducing the exercise-induced depletion of tryptophan levels that occur after excessive exercise. Tryptophan is a precursor of serotonin, a neurotransmitter involved in mood regulation as well as gastrointestinal function. Psychobiotics is a newly coined term for the probiotics that positively influence the gut-brain axis where microbes and mind network.


    It takes more than strong lungs and legs to run a marathon. Healthy microbes are crucial to prevent leaky gut, immunosuppression, inflammation, and depression.

    Probiotics offer an effective strategy to prevent or improve those symptoms and allow for athletic success without the downsides.  Eat fermented foods daily and take a high-dose multi-strain supplement during training.

    And then run like the wind.

    Note: The views and opinions expressed here are those of the author(s) and contributor(s) and do not necessarily reflect those of the publisher and editors of WholeFoods Magazine.

    Clare Fleishman RDN, MS is a Registered Dietitian with the Academy of Nutrition and Dietetics and holds a master degree in nutrition science. She bridges the gap between science and health across most platforms: major newspapers, magazines, books (Globesity), workshops, social media and websites. From corporate whiteboards to refugee schools in Egypt, Fleishman agitates for personal and public change.  In 2010, she launched to share the cascade of new discovery in the microbiome. Always amazed at this “forgotten organ” Fleishman also creates white papers, blogs, videos and social media for the International Probiotics Association as well as continuing education platforms.