Gut check: how exercise shapes the microbial community in our gut


Breaking down the microbiology world one bite at a time

Gut check: how exercise shapes the microbial community in our gut

At some point in our lives we have all looked in the mirror and seen a few flaws in our appearance. Maybe a fat belly or flabby arms. This may have motivated some to work out or pushed some of us into sadness. Rarely does it happen that we look underneath the physical appearance. How does our sedentary lifestyle impact our digestion? Do we fall sick frequently? How does it affect our brain? Or our mood? Similarly, the people who have intense work out sessions, especially athletes, are they really healthy from inside? Can intense exercising have negative effects too? Let’s dive in!

What is gut microbiota? How does it help us?

Think of your gut microbiota as a community of tiny organisms that live in your digestive system. They help to keep your body healthy. One of their main jobs is to protect your gut lining from harmful bacteria and viruses. They do this by producing antimicrobial factors that stop bad bacteria from growing and spreading. It’s like having a security team that keeps the bad guys out of your house.

Gut microbiota also has a connection to your immune system. It helps your immune system to function properly. They stimulate your body to produce antibodies that help fight off infections. They also produce vitamins that the body needs to stay healthy. Another important thing they do is to help you digest food. 

The composition of these microbes in your gut starts from the time you were born and changes into adulthood.  It changes throughout life and is influenced by various factors, including birth delivery procedures, nutrition, and host factors such as lifestyle and medication. Just like a garden needs the right conditions, like soil, sunlight, and water, to grow healthy plants, the gut microbiota also needs the right conditions, such as the right balance of bacteria and nutrients, to thrive. Different plants require varying conditions to grow, and likewise, distinct types of bacteria flourish in diverse gut conditions.

GUT, BRAIN, AND MUSCLES- What’s the connection?

Our gut, brain, and muscles are interconnected through a complex network known as the gut-brain-muscle axis. The gut and the brain communicate with each other through a bidirectional pathway known as the gut-brain axis. The gut microbiota plays a vital role in this communication. They produce various metabolites that can influence the brain’s function and behaviour by interacting with the nervous system, immune system, and endocrine system. On the other hand, the brain can also influence the gut microbiota by sending signals through the vagus nerve, which connects the brain to the gut.

The HPA axis (Hypothalamus-Pituitary-Adrenal), which is a major stress-response system in our body, also plays a crucial role in this connection. When we are under stress, the HPA axis releases cortisol, which can affect the gut microbiota and the brain. High levels of cortisol can lead to changes in the gut microbiota, which can in turn affect the brain and vice versa. Good news is exercise can help to reduce stress by regulating the HPA axis and releasing endorphins, which are natural painkillers and mood enhancers. When we exercise, our muscles produce various molecules such as cytokines and myokines that can influence the gut and the brain. Cytokines can cause inflammation in the gut. Whereas, myokines can have positive effects on the body by promoting tissue repair and reducing inflammation. These molecules can also affect the gut microbiota and the HPA axis. 

Each rigorous and extended period of training creates physical strain and temporary yet significant modifications in immune defence, resulting in increased release of stress hormones, pro- and anti-inflammatory cytokines, and reactive oxygen species. These changes can impact: a) natural killer cell activity, b) the quantity and proper function of T and B cells, c) the function of neutrophils in the upper respiratory tract, d) the concentration of IgA in saliva, and e) the oxidative actions of granulocytes. MHC expression is reduced for a few hours during recovery after prolonged endurance exercise. Therefore, changes in hormone levels (such as an increase in cortisol secretion), repetitive muscle damage, and insufficient energy can produce unpredictable effects on immune system regulation and intestinal microbial imbalances. Image Credit- Wegierska, A. E. et al (2022)

Impact of Intense Exercise on Gut Bacteria: Athletes vs Non-Athletes 

When physical activity is too much for the body to handle it may lead to opposite results than the benefits that it provides. Keep in mind, high-intensity physical activity is exercise that is done at a level that is at least 80% of your maximum heart rate or 70% to 90% of your maximum oxygen uptake.

Studies have shown that intense exercise can lead to changes in the gut microbiota composition, promoting dysbiosis that favours inflammation and negatively impacting the body’s metabolic balance. The negative effects of intense exercise on the gut microbiota can lead to gastrointestinal symptoms such as nausea, cramps, diarrhoea or constipation, bloating, leaky gut syndrome (LGS), and even bleeding. Although the severity of the symptoms experienced by athletes during intense exercise including the athlete’s physiologic conditions, the intensity and duration of the specific training activity, and the adequate nutrition plan according to the sports disciplines. 

A study on a 32-year-old male marathon runner found that intense physical activity during a 163-km mountain race had a significant impact on his gut bacteria. After the race, there was a decrease in some types of bacteria and an increase in others. Specifically, there was a decrease in Bacteroides, Subdolingranulum, and Alloprevotella species, and an increase in Pseudomonadota, Haemophilus, Veillonella, and Streptococcus species. Veillonella plays a key role in the lactic acid cycle, while Haemophilus can host various harmful species. Although the runner did not report any symptoms of gastrointestinal infection or inflammation, the study suggests that the proliferation of these pathogens in the gut may contribute to infections in athletes who undergo prolonged and intense physical exercise.

Another study examined the gut microbiome of 40 elite rugby players (mean age= 29) and compared it to the gut microbiome of non-athletes. They found that rugby players had a higher ratio of Bacteroidota/Bacillota phyla, which are known to fight obesity! The study suggested that this may be due to the athletes’ high-protein diets and intense physical activity, which could promote the growth of these particular bacterial phyla.

This means that regular physical activity can help keep the gut bacteria in a healthy balance, which can improve overall health. On the other hand, intense and irregular training, like what professional athletes often experience, can disrupt the balance of gut bacteria and negatively affect performance. Get ready to keep your gut in check! Regular exercise is key to keeping those gut bacteria happy and healthy. But be careful, too much intense and sporadic training can actually hurt you. Although probiotics present a potential solution. They can introduce good bacteria to the gut, which pushes out the bad ones and improves your overall gut health. Studies have shown that probiotics can even help with issues like irritable bowel syndrome and inflammatory bowel disease. 

What the Everyday Person Should Take Away from this Study?

In conclusion, gut bacteria have an important role in overall health and well-being. Oftentimes professional and amateur athletes have to train rigorously. Without proper rest intervals and diet, it can do more harm than good.  And if you’ve been taking antibiotics, feeling stressed, or eating poorly, probiotics can help restore balance to your microbiome. So go ahead and get moving, and let probiotics give your gut the boost it needs!

Link to the original post: Wegierska, A.E., Charitos, I.A., Topi, S. et al. The Connection Between Physical Exercise and Gut Microbiota: Implications for Competitive Sports Athletes. Sports Med 52, 2355–2369 (2022).

Other references: Clarke SF, Murphy EF, O’Sullivan O, et alExercise and associated dietary extremes impact on gut microbial diversityGut 2014;63:1913-1920. 10.1136/gutjnl-2013-306541    

Featured image: Made by author using Inkspace and image by studiogstock on Freepik