Wendy Martinson, performance nutritionist, explains how probiotics could be beneficial to the human gut, and specifically for athletic performance.
What are probiotics?
The human gut is inhabited by over 40 trillion bacteria,1 which play a key role in various aspects of human physiological function such as nutrient uptake, vitamin synthesis, energy yield, inflammatory modulation, and host immune response.2 The intended use of probiotics is to influence this vast microbiota in the gut for the benefit of human health.
The word 'probiotic' comes from the Greek and means 'for life'.3 The term is used to describe live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.4 Species of Lactobacillus and Bifidobacterium are most commonly used as probiotics.1
Creating a healthier gut environment is one of the main advantages of probiotics. This can occur via their effect on the development of the microbiota residing in the gut, so promoting proper balance between pathogens and the bacteria that are necessary for normal gut functioning.
There are many recognised benefits of probiotics, and results of clinical studies demonstrate their favourable effect on certain conditions such as gastrointestinal diseases (irritable bowel syndrome, gastrointestinal disorders, elimination of Helicobacter, inflammatory bowel disease, diarrhoeas) and allergic diseases (atopic dermatitis), as well as positive effects on human health through influencing the body's immune function.3, 5
A study by Hao et al in 2015 showed that probiotics have also been shown to be superior to placebo in reducing acute upper respiratory tract infections (URTI), and research is ongoing relating to specific strains and GI conditions: Lactobacillus paracasei LPC- 37, Lactobacillus rhamnosus GG, Lactobacillus Acidophilous NCFM and Bifidobacterium. animalis. subsp. lactis BI-04 have all been found to have benefits in the management of antibiotic-associated diarrhoea, and Lactobacillus Paracasei LPC-37 and Lactobacillus Acidophilous NCFM in the treatment of functional constipation.1
Individual types of probiotics are named by genus, species, subspecies (if applicable) and an alphanumeric designation that identifies a specific strain. For example, Bifidobacterium (genus) animalis (species) lactis (subspecies) BI-04 (strain). This enables specific strains to be identified and linked to particular health benefits.
It is likely that different strains, species or genera may share some similar mechanisms of action. For example, the ability to produce organic acids, such as lactate and acetate, is common in most species of both Bifidobacterium and Lactobacillus. These acids are important as they inhibit the growth of undesirable microbes and cross-feed beneficial microbes, leading to the production of butyrate, an important fuel for the intestinal cells.6
Probiotics for athlete health
Athlete health can be affected by numerous factors such as intense and extensive training, lack of rest, frequent travel and compromised nutritional intake. Common issues include gastrointestinal (GI) symptoms, oxidative and mental stress, increased risk of upper respiratory tract infections (URTI) and dysregulation of immune and inflammatory responses.7, 8
Various food-based nutrition strategies can be implemented to support the challenges faced by athletes, and the addition of a probiotic supplement may complement this.
A selection of different strains of probiotics have been studied in athlete groups, and it is suggested that a minimum intervention time is needed to affect the immune response. It is generally understood that it takes around 14 days for probiotics to colonise the GI tract,9 and so this should be factored into any supplementation strategy.
A multi-strain probiotic formulation may increase the likelihood of adhesion and colonisation of probiotic strain in the GI tract, and could reduce the duration of supplementation required to achieve impact.
Strains that are compatible with each other may also work together synergistically. Haywood et al (2014) found that four weeks' supplementation of a probiotic mix containing 3 strains of bacteria at a dosage of 3 x 109 (3 billion) colony forming units (CFU) significantly reduced the number of URTI or GI episodes of elite rugby union players compared to placebo.10
West et al. (2013) investigated the impact of probiotic supplementation for 150 days on symptoms of respiratory and gastrointestinal illness in healthy physically active adults. The study compared the impact of a single strain of a probiotic (Bifidobacterium. animalis. subsp. lactis BI-04) and a multi-strain probiotic (Lactobacillus. acidophilus NCFM and Bifidibacterium. animalis subsp. lactis Bi-07) against placebo.
Analysis of results showed a significant reduction in the risk of 27% of any URTI episode in the BI-04 group and although not significant, there was a reduction in the risk of 19% in the NCFM and Bi-07 group compared to placebo.11
Kekkonen et al. (2007) investigated the effect of supplementation of the probiotic strain Lactobacillus rhamnosus GG compared to placebo on respiratory infection and gastrointestinal symptoms of 141 marathon runners.
The daily dose for 3 months was either 1 x 1010 if capsules were taken or 4 x 1010 if a drink option was taken. There was no effect on the incidence of URTI, but there was a shortening in the duration of gastrointestinal symptom episodes.12
Recommended doses of probiotics cannot be generalised, but should be based on those that have been used in studies showing a benefit.3 Dosing ranges have been reported in the literature between 1 x 109 and 4 x 1010 and the 2018 IOC consensus statement suggests 1010.13
In summary, as in many areas of sports nutrition, there is still much more research to be done in this field. However, from the current literature there appears to be great potential for both single-strain and multi-strain probiotics to have a positive impact on the health and wellbeing of athletes, especially in relation to gut and immune function.