The gut microbiota and exercise

In recent years there has been an exponential increase in research into gut microbiota and its health implications.

Growing evidence suggests that commensal and pathogenic bacteria, and their metabolic by-products (e.g., short chain fatty acids and structural residues (e.g. endotoxins)), may attenuate or exacerbate pathophysiologic pathways of many clinical conditions. Browse gut microbiota to find out more.

It’s worth noting that the key messages from this document are:

• Bacterial numbers and diversity increase along the gastrointestinal tract- from the stomach to the colon.

• There exists differences in the bacterial numbers and composition sectional from the lumen to the epithelial atypic surface

• Bacterial numbers and diversity change through life, with accelerated growth in the first year, then slow increase until a plateau. During transition into adulthood and throughout adulthood bacterial numbers and diversity are stable, but change dynamically depending on lifestyle factors (e.g., individual variant, diet, exercise, circadian and seasonal variations, stress and trauma, etc.).

What is considered a healthy gut microbiota profile?

1. ↑ α-diversity (e.g. Shannon index).

2. ↑ relative abundance of SCFA producing bacteria.

3. ↓ relative abundance of pathogenic endotoxin producing bacteria.

4. Health specific associations: Firmicutes:Bacteroidetes ratio, E.coli sepsis, Clostridium leptum groups (e.g., Faecalibacterium prausnitzii) in IBD.

What are the functions of SCFA (e.g., butyrate C4, propionate C3, and acetate C2)?

• Nutrient production, digestion and absorption.
• luminal, epithelial, and systemic immunity.
• ↑ intestinal epithelial integrity (e.g., mucosa, cell and tight-junction complex).
• Gastrointestinal motility and peristalsis.

What we know

From an exercise perspective, previous research has predominantly explored the gastrointestinal bacterial taxonomy of athlete groups at rest, and (or) assessed changes in bacterial taxa induced by exercise training (e.g., 30-60 min·day^-1 for 3-weeks) in health sedentary (lean and obese) or cardiometabolic risk populations.

Although the impact of exercise on resting gut microbiota status in active populations seems promising (e.g., increase α-diversity and relative abundance of short chain fatty acid producing bacterial groups), there appears to be substantial heterogeneous bacterial taxa outcome between studies, possibly associated with varying levels of confounding factor control (e.g., dietary differences, training and rest period, seasonal variation, and degree of supplement use, etc.) and differing methodologies used (e.g., faecal collection, processing, analysis, and data management).

Therefore, at present the establishment and confirmation of a so-called ‘healthy gut microbiota profile’ in athletes is not possibly and clearly evidence, and likely to be dynamic and individually responsive.

What role does gut microbiota play?

The gut microbiota may play a role in modulating exercise-induced gastrointestinal syndrome through increasing are diversity and relative abundance of intestinal commensal bacterial (e.g., Akkamensia, Bacteroides, Bifidobacterium, Lactobacillus, Rosburia and Faecalibacterium) producing short chain fatty acids (i.e., butyrate, acetate, and propionate) and other metabolic by-products (e.g., anti-inflammatory factors) reported to stimulate luminal host immunity (e.g., luminal secretion of anti-microbial proteins and activation of innate immune responses), enhance intestinal epithelial structural barrier (i.e., mucus production, enterocyte cell proliferation, and tight-junction proteins expression), reduce pathogenic adhesion to intestinal epithelial apical surface, and improved gastrointestinal motility including facilitating peristalsis.

In addition, reduction of bacteria structural residues (e.g., endotoxins- lipopolysaccharide, peptidoglycan, flagellin, lipoteichoic acid, and muramyldipeptide) that are common on pathogenic bacteria (e.g., Escherichia, Salmonella and (or) Campylobacter), and are potent stimulators of local epithelium and systemic immune responses (via Nfκβ and phagocytic immune cell activation), through the TLR-4 activation pathway identifying pathogen-associated molecular patterns on pathogenic bacterial surfaces.

Research outcomes from Monash University

To date the only research that has explored the link between the gut bacterial composition and EIGS is from the Monash University team. The following describes outcomes from the research.

Research outcome 1

Greater α-diversity and presence of several commensal bacterial groups was associated with a favourable, but modest, effect on the magnitude of perturbations to gastrointestinal integrity and symptoms, and potentially favourable tolerance to thermoregulatory strain, in response to exertional-heat stress.

Research outcome 2

The human gut microbiota composition may play a role in amelioration or exacerbation of exercise-induced gastrointestinal syndrome, and therefore should be a consideration within the pathophysiological and exacerbation assessment procedures of athlete reporting exercise-associated gastrointestinal symptoms.

Research outcome 3

No one singular commensal or pathogenic bacterial taxa was identified as a key association microorganism. At present, associations between the gut microbiota with exercise-induced gastrointestinal syndrome and subsequent gastrointestinal symptoms, and relevant performance and clinical outcomes, the bacterial diversity appears to present a potential beneficial outcome.

Research outcome 4

Future research is warranted to justify and establish the extent and need for human gut microbiota modifiers (e.g., diet, exercise, supplementation, and (or) pharmaceuticals) prior to exertional or exertional-heat stress with the aim of optimising bacterial taxa targets for exercise-associated gastrointestinal symptom amelioration, this clinical and performance implications.

Research outcome 5

Despite recent animal research showing exercise performance improvements in mice treadmill testing with a singular bacteria species (Veillonella atypica) and short chain fatty acid (i.e., propionate) interventions, proposed through lactate pathway mechanisms, any substantial implications on human performance would be via reductions in debilitating gastrointestinal symptoms, and not necessarily through a metabolic pathway that is not performance limiting in human athletes.

Find out more

Consider exploring Exercise and the Gut Microbiome: A Review of the Evidence, Potential Mechanisms, and Implications for Human Health, Meta-omics analysis of elite athletes identifies a performance-enhancing microbe that functions via lactate metabolism or Does the gut microbiota bacterial abundance and composition influence the magnitude of intestinal integrity perturbations, systemic cytokinaemia, and gastrointestinal symptoms in response to exertional-heat stress? to find out more about this research area.