Research shows that a healthy gut microbiome can be beneficial for many aspects of overall health, wellness, and longevity. Optimizing gut health can promote immune system health, reduce inflammation, balance hormones, and improve the digestion and absorption of food—all actions that are also important components of being a healthy athlete. So, is there a connection between gut health and performance? Here's a synopsis of what the science says about the connection between a healthy gut and optimized athletic and physical performance.
Why is the gut microbiome critical in athletic performance?
The gut microbiome can contribute to athletic performance both during and after intense exercise. First, an optimal gut microbiome can improve energy metabolism by supplying muscles with oxygen and nutrients during intense exercise. The gut microbiome can then also control inflammation and expedite tissue repair, helping to improve performance and expedite recovery.  
A healthy, well-fed gut can provide energy during exercise
Energy availability is an important limiting factor during intense exercise—the more energy available in the body, the more work you'll be able to do. So, during prolonged physical activity, the body needs to tap into various energy sources to maintain or exceed load. Luckily, a healthy microbiome can contribute to this energy supply. When gut microorganisms break down and derive energy from food, they produce short-chain fatty acids (SCFAs). These SCFAs act as a substrate for a process called gluconeogenesis, which generates glucose for muscles to use as energy. A 2021 review confirmed that these SCFAs may be a critical factor in endurance performance, but more research in humans, particularly athletes, is needed. 
Despite the established importance of gut health on physical performance, athletes are at particular risk of damaging the microbiome by underfueling. It’s well-established that athletes have higher overall energy and nutrient needs than sedentary people, which is just a part of what makes them prone to the risk for underfueling. Underfueling or restrictive eating habits can lead to GI issues by a number of mechanisms.
It is also important to feed the good gut microbes with prebiotic, fiber-rich foods to promote gut health.  Examples of these foods include whole grains, legumes, fruits, vegetables, nuts, and seeds. If an athlete is following a restrictive diet or falling short on these foods in particular, these gut microbes won’t have the fuel they need to thrive.
A healthy gut can help reduce inflammation
The gut microbiota can mitigate inflammation, which is of critical importance for athletic performance. Exercise naturally induces muscle fiber tears, causing inflammation. During the repair process, blood flow increases to the affected area to replenish oxygen, fuel our muscles, and clear out waste, allowing our muscles to repair and grow. And while some inflammation is critical for the muscle-building process, prolonged inflammation can be detrimental to the immune system.
But a healthy gut can counteract the potential for excess inflammation brought on by intense exercise. As mentioned earlier, a well-fed microbiome produces SCFAs which contribute to energy usage.  But these molecules play yet another role: research has shown that SCFAs produced by healthy gut microorganisms can counteract inflammation brought on by intense exercise by reducing gut permeability and inhibiting cytokines, a type of inflammatory molecule. This mitigation of inflammation can also help to delay fatigue post-exercise. 
How athletes can support gut health
Like many topics in the sports nutrition world, further research is needed to understand the relationship between physical activity and the gut microbiome more deeply. In the meantime, there are actions you can take as an athlete to promote a healthy gut microbiome:
Prioritize sleep: It’s critical that athletes get adequate sleep to maximize recovery and performance. A diverse gut microbiome is associated with increased sleep efficiency, increased total sleep time, and decreased mid-sleep awakenings.
Fuel up: Adequate intake of macro and micronutrients and diverse food groups can help support athletic performance and overall health. Restrictive diets or those which exclude entire food groups (oftentimes carb sources) can deprive good gut bacteria of the prebiotic, fiber-rich foods they need. In addition, polyphenol-rich foods can positively impact the gut microbiome.  These include coffee, tea, wine, and cocoa.
Manage stress: This includes both life and training stress. Increased levels of cortisol, the stress hormone, have been associated with poor gut health, digestive problems, and loss of muscle tissue. They can also lead to poor sleep quality, increased anxiety, poor mood, decreased bone density, and reduced immune system function.
Monitor your biomarkers: In addition to cortisol, a number of blood biomarkers are associated with gut health. Monitoring hsCRP, HDL cholesterol, triglycerides, glucose, and HbA1c and taking the recommended actions to optimize these markers can help to improve your gut microbiome.
Probiotics may be warranted: Probiotics are beneficial microbes that may help lower inflammation levels, promote weight maintenance, and improve mood and cognition.[9,10,11] Probiotics also have the potential to promote health in athletes and improve physical performance and exercise capacity. While there are many potential benefits from probiotics, more research in athletes is necessary to learn more about the roles that probiotics play in physical performance and the modes of action behind these potential benefits. 
An active lifestyle may also support gut health
The gut microbiome can support athletic performance, but the opposite may also be true. Studies have shown that gut microbiome diversity (a marker of good gut health) is characteristically higher in active individuals than sedentary ones.  Body composition and physical activity are also positively correlated with several specific bacterial strains.
While more research is needed to untangle the relationship, researchers have identified multiple possible modes by which an active lifestyle may impact gut health. These include:
- Higher amounts of health-promoting or ‘good’ gut bacteria
- More diversity of the good gut bacteria
- Increased metabolic capacity
- Improved GI barrier function
- Improved mucosal immune function (remember, the gut is part of the immune system!)
Athletes also have more fecal metabolites—the end products from gut bacteria's metabolism of food and nutrients—that are associated with increased muscle turnover (or fitness level) and overall health than less active individuals.  In turn, athlete gut microbiomes may improve capacity for tissue repair and a greater ability to use energy from the diet, as mentioned earlier.
Interestingly, there also may be a difference in gut health associated with different types of sports. A study of elite athletes across sixteen different sports found that, when diet was kept consistent, sport type and training load contributed to differences in the gut microbiome. 
A summary of the research on the gut microbiome and athletic performance:
- Having an optimized gut microbiome can improve energy metabolism during exercise.
- Healthy gut microbiota also can mitigate inflammation and delay post-exercise fatigue.
- Underfueling or restricting intake can negatively impact an athlete's gut health.
- Athletes may have a more diverse gut microbiome than the general population.
- The gut microbiome can vary across different types of sport or training loads.
- More research is needed to further understand the relationship between physical activity and the gut microbiome.
Stevie Lyn Smith, MS, RDN, CSSD, CDNStevie Lyn is a Content Strategist and Team Nutritionist at InsideTracker. As a Registered Dietitian and Ironman triathlete, she enjoys combining her passions to help educate others on how to fuel for overall health and performance. When she’s not swimming, biking, or running with her dog, you’ll find her in the kitchen working on a new recipe to improve her biomarkers.