Microbiome Research in Cycling: The Impact of Endurance Training on Gut Microbiota

Introduction

The human gut is home to over 100 trillion microorganisms, with a total gene count roughly 150 times that of the human genome. This “second genome” is known as the gut microbiota, and it has profound effects on the immune system, metabolic function, and even mental health. In recent years, sports science research has begun to focus on a new question: Does endurance training alter the gut microbiota, and does this change affect athletic performance?

For cyclists, gut issues are themselves a major factor influencing performance—according to statistics, approximately 30–50% of endurance athletes experience gastrointestinal discomfort (nausea, diarrhea, abdominal cramps) during competition. Understanding the bidirectional relationship between the gut microbiota and training may be the next frontier in optimizing athletic performance.

The Impact of Endurance Training on Gut Microbiota

Characteristics of Athletes’ Gut Microbiota

A landmark study by Clarke et al. (2014) published in the journal Gut compared the gut microbiota of professional rugby players, moderately active adults, and sedentary adults:

• Athletes had significantly higher microbial diversity (Alpha Diversity) than both control groups
• Higher proportions of specific beneficial genera (such as Akkermansia and Bifidobacterium)
• Greater abundance of genera associated with short-chain fatty acid (SCFA) production

Further research on cyclists (research direction by Mitchell et al., 2019) found:

• Amateur riders cycling > 10 hours per week had significantly better gut microbiota diversity than those cycling < 3 hours per week
• The abundance of Ruminococcaceae family bacteria (involved in fiber breakdown and SCFA production) was positively correlated with VO₂max

Differential Effects of Exercise Intensity

The “Leaky Gut” Issue in High-Intensity Training

During high-intensity riding, blood is redistributed to working muscles, and intestinal blood flow can decrease by 60–70%. This causes transient ischemia of the intestinal mucosa, leading to a phenomenon known as “increased intestinal permeability (Leaky Gut)”:

• Toxins such as bacterial lipopolysaccharides (LPS) may leak into the bloodstream
• Triggers a systemic low-grade inflammatory response
• Directly linked to the nausea and diarrhea symptoms experienced after races

Short-Chain Fatty Acids (SCFA) and Athletic Performance

The Key Metabolic Role of SCFAs

Short-chain fatty acids (primarily acetate, propionate, and butyrate) are metabolic products of gut bacteria fermenting dietary fiber. Their importance for athletes includes:

• Butyrate: The primary energy source for intestinal mucosal epithelial cells, maintaining intestinal barrier integrity
• Propionate: Converted in the liver into a substrate for gluconeogenesis, indirectly supporting blood glucose stability during exercise
• Acetate: A potential energy source for cardiac and skeletal muscle

Research on Microbiota and SCFA Production

Recent metagenomic studies (analyzing microbiota through DNA sequencing) show:

• Veillonella atypica (a lactate-converting bacterium) can convert lactate produced during exercise into propionate, theoretically forming a positive feedback loop of energy reuse
• A 2019 study in Nature Medicine found that Boston Marathon runners had significantly increased gut Veillonella abundance after the race
• However, the applicability of these findings to cyclists still requires further research

The Bidirectional Relationship Between Gut Health and Training

Endurance training → Improved gut microbiota → Better energy metabolism → Better training adaptation → Continuous positive cycle
     ↑                                                      |
     └──────────────── Increased SCFA production ──────────────────────┘

But there is also a risk of a negative cycle:

Overtraining → Increased intestinal permeability → Inflammatory response → Reduced recovery capacity → Decreased training tolerance

Dietary Strategies and Their Microbiota Effects

Practical Recommendations

1. Dietary diversity during the season: During training periods, focus on a variety of fruits, vegetables, and whole grains to maintain a foundation of gut microbiota diversity
2. Probiotic supplementation strategy: Research supports supplementing with probiotics containing Lactobacillus rhamnosus for 4–8 weeks before long-distance events, which may reduce gastrointestinal discomfort
3. Gut protection after high-intensity training: Consuming polyphenol-rich foods (berries, dark chocolate) after high-intensity sessions may help reduce intestinal inflammatory responses
4. Avoid trying new foods before races: Maintain a familiar dietary pattern for 48 hours before competition to reduce microbiota fluctuations
5. Monitor the relationship between training load and gastrointestinal symptoms: If gut issues occur frequently, it may be a warning sign of overtraining

Conclusion

Gut microbiota research has opened a new door for cycling sports science. From microbial diversity to the metabolic recycling of short-chain fatty acids, the gut is no longer just a digestive organ but an important component of the athletic performance system. As microbiome technologies (Microbiomics) become more accessible, personalized “gut microbiota optimization diet plans” may become a standard part of elite cyclists’ preparation protocols in the future.

Related Reading

• Gut Microbiota and Cycling Performance: How the Microbiome Affects Your Endurance
• Microbiome and Exercise: New Research on Gut Microbiota and Endurance Performance
• Gut Health in Swimmers: The Impact of Probiotics and Gut Microbes on Immunity
• Gut Microbiota and Endurance Performance: How the Microbiome Affects Energy, Inflammation, and Recovery