John Davis

Written by John Davis


Probiotic Supplements for Runners: The Definitive Guide

One of the most exciting frontiers in medical research is on the gut microbiome, the population of “good bacteria” inside your body that are linked to everything from gastrointestinal health to the function of your immune system.

Supplements that boost the population of these good bacteria are known as probiotic supplements or just “probiotics” for short, and they’ve rapidly become incredibly popular.

Runners are understandably interested in the potential benefits of a healthy population of gut bacteria—a healthier gut could promise fewer illnesses and gastrointestinal problems during training and racing.

Exercise already helps improve your gut bacteria populations

Over the past decade, research has definitively established that athletes have a healthier and more diverse gut microbiome than people who do not exercise.

One study published in 2014 in the journal Gut examined the microbiomes of professional rugby players and matched non-athletic controls, and found substantially greater variety in the types of beneficial bacteria in the digestive tract of the athletes [1].

Moreover, the researchers found a correlation between greater protein consumption and greater bacterial diversity.

Even with this greater bacterial diversity, athletes (including runners) do face additional stresses on their body during training.

As such, could runners benefit from a probiotic supplement? In this article, we’ll explore the research.

What the research says about probiotic supplementation in runners

New research that is specifically focused on probiotic supplements in runners suggests some very promising applications.

Reducing risk of getting sick

Specifically, probiotics could help reduce the risk of getting sick during tough training blocks, and they could also help prevent gastrointestinal problems like cramping, bloating, and diarrhea, both during training and racing.

On the illness front, a study published in 2010 by a team of researchers at the Australian Institute of Sport tested the effects of a probiotic supplement in 20 elite distance runners [2].

Half the runners received a placebo, while half received a supplement containing Lactobacillus fermentum bacteria. After two months, the groups were switched, so all of the participants took both the placebo and the probiotic.

When the runners were on the placebo, they racked up a total of 72 days of symptoms from respiratory illnesses like the cold and the flu, but when they were on the probiotic supplement, they only experienced a total of 30 days of symptoms.

The over-50% reduction in this study is pretty impressive, and suggests that probiotics could be a useful way to avoid illness in the lead-up to a big race or during a tough training block.

Improving stomach issues

Scientific evidence also indicates that probiotic supplementation could help reduce gastrointestinal problems like bloating, nausea, and diarrhea.

One study published in the International Journal of Sport Nutrition and Exercise Metabolism in 2007 studied nearly 150 marathon runners over the course of a three-month training period [3].

This time, the researchers used a probiotic based on Lactobacillus rhamnosus bacteria in half of the runners, comparing it with a placebo given to the other half of the participants.

Gastrointestinal tract symptoms were lower in the probiotic group both before and after the marathon (though notably, the number of respiratory infections were the same in both groups).

Probiotics might help you out on race day, too, at least according to a study published this year by a team of researchers in the UK [4].

The study gave 24 recreational runners either a placebo or a combination of three probiotic bacteria strains in the months leading up to a marathon.

The runners were polled on the incidence of gastrointestinal problems both leading up to the marathon and during each third of the race itself. The researchers also tracked how much the runners slowed down in the final third of the race to get an objective measurement of whether the probiotic supplement had a performance benefit.

While the probiotic supplement had no effect on overall finish times, the runners who were taking the probiotic supplement reported fewer gastrointestinal problems in the two weeks leading up to the race, and fewer problems in the final third of the race.

Moreover, the runners in the probiotic group slowed down less than the runners in the placebo group—perhaps because of fewer bathroom-related interruptions.

Using probiotic supplements to help your running

The results we’ve seen so far are promising, but it’s still far from clear how to actually supplement with probiotics to help your running.

There’s a huge variety of potential probiotic strains (i.e. types of different bacteria) you could take, and wildly varying dosages too.

Some guidance comes from a review article published in 2015 in the European Journal of Sports Science by David B. Payne and other researchers, which provides some much-needed practical tips from experts [5].

When it comes to the strains of probiotic bacteria, the lion’s share of the research conducted on athletes thus far has used strains from the Lactobacillus and Bifidobacterium families.

Look for strains like Lactobacillus rhamnosus, Lactobacillus casei, Lactobacillus fermentum, and Bifidobacterium animalis.

Dosages for probiotics are measured in CFUs, which stands for “colony-forming units”—essentially, this is how many live bacteria are present in a single dose.

Research on athletes typically uses doses of 12 to 40 billion CFUs per day.

This same review article also provides some useful advice on day-to-day use of probiotic supplements.

First off, it’s important to remember that probiotics contain living bacteria, which could be killed if you are careless with your supplement.

Keep the bottle in a cool, dark place, out of direct sunlight and away from heat. The best place to keep a probiotic supplement would be your refrigerator (and the worst place would be your car on a hot summer day).

According to Payne and his colleagues, you should start taking a probiotic supplement at least two weeks before a race or the start of a serious block of training—it can take at least 14 days for changes in your gut bacteria to appear.

Moreover, you shouldn’t be surprised if you have some transient gas or stomach rumbling in the first few days after you start taking a probiotic, as your body adjusts.

There’s still quite a lot we don’t know about probiotics, health, and performance in runners, but so far, the scientific research indicates that they could be useful for reducing training time lost due to illness, and lowering the rate of gastrointestinal problems, both in training and during long races.

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1. Clarke, S.F., Murphy, E.F., O'Sullivan, O., Lucey, A.J., Humphreys, M., Hogan, A., Hayes, P., O'Reilly, M., Jeffery, I.B., Wood-Martin, R. and Kerins, D.M., 2014. Exercise and associated dietary extremes impact on gut microbial diversity. Gut, 63(12), pp.1913-1920.

2. Cox, A.J., Pyne, D.B., Saunders, P.U. and Fricker, P.A., 2010. Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes. British Journal of Sports Medicine, 44(4), pp.222-226.

3. Kekkonen, R.A., Vasankari, T.J., Vuorimaa, T., Haahtela, T., Julkunen, I. and Korpela, R., 2007. The effect of probiotics on respiratory infections and gastrointestinal symptoms during training in marathon runners. International Journal of Sport Nutrition and Exercise Metabolism, 17(4), pp.352-363.

4. Pugh, J.N., Sparks, A.S., Doran, D.A., Fleming, S.C., Langan-Evans, C., Kirk, B., Fearn, R., Morton, J.P. and Close, G.L., 2019. Four weeks of probiotic supplementation reduces GI symptoms during a marathon race. European Journal of Applied Physiology, 119(7), pp.1491-1501.

5. Pyne, D.B., West, N.P., Cox, A.J. and Cripps, A.W., 2015. Probiotics supplementation for athletes–clinical and physiological effects. European Journal of Sport Science

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