leaky gut

Athletes and Inflammation – when is it too much?

The gut is an often overlooked part of the body that regulates inflammation. Athletes training with heavy loads are at an increased risk for infection, which requires them to pay greater attention to nutritional strategies used to mediate inflammation. This recovery should include probiotics, which have demonstrated to be a promising nutritional intervention to control and alleviate inflammation.  

Before reading this blog, check out Immunity and Worldwide Competition because it explains how probiotics strengthen immunity and gut health, which will help you understand this blog’s discussion of probiotics and inflammation. 

In this blog, we will explain: 
The process of inflammation

The association between exercise and inflammation

How probiotics regulate inflammation

Probiotics and their effect on exercise-induced airway inflammation and infection


Inflammation is a protective reaction by the body in response to an injury or infection. It results in increased blood flow to the problematic area (redness), increased body temperature (heat), fluid accumulation and pain (caused by the release of chemicals from damaged cells). 

For athletes, exercise-induced muscle damage accompanied with inflammation may first come to mind when thinking about inflammation in general. This acute muscle inflammation from intense or prolonged training occurs when muscles undergo small micro-tears (i.e., small injuries) that cause an acute inflammatory response. Acute inflammation is not a serious problem, and the body repairs this following a workout. It is actually thought to be a part of the normal adaptation to exercise. 

It is the underemphasized chronic inflammation in the gut that may disrupt normal body functions and impair adaptations to exercise. Chronic inflammation results from stressors (e.g., heavy training, poor quality sleep, alcohol, unhealthful diet, etc.) and poor recovery from intensive training – in turn, overtraining. Poor gut health can lead to inflammation in the body, and probiotics are a recovery tool that may mitigate the negative effects of chronic inflammation and reduce the risk of overtraining. 

Exercise & Inflammation

Endurance exercise impacts inflammation throughout the body. Intense training causes acute inflammation, which is comparable to what results in patients with sepsis (i.e., inflammation throughout the body when the body releases chemicals to fight an infection) and trauma. Strenuous exercise increases the amount of pro-inflammatory cytokines, such as TNF-alpha, IL-1, IL-6, TNF receptors and anti-inflammatory modulators such as IL-10 and IL-8. 

Endurance exercise reduces the flow of blood, oxygen and nutrients to the gut, increases the permeability of the gut wall and lowers the thickness of the gut mucosal layer, which results in an inflammatory immune response – “leaky gut.” This is why the mucosal immune system has an important function – to control responses to antigens, which will control inflammation. 

The inflammatory responses generated from intense exercise are fought by gut microbiota and their short-chain fatty acids (see below) that reduce gut permeability and stop the release of inflammatory cytokines. It is suggested that the anti-inflammatory effects of gut microbiota may help delay fatigue during endurance exercise. 

Exercise-Induced Airway Inflammation

One of the consequences of prolonged inflammation is impairment of the immune system. Upper respiratory tract infections (URTIs) (e.g., the common cold and inflammation of the trachea and larynx) are common among highly trained and elite athletes because they are more susceptible to weakened immune systems. The causes of URTIs are considered unclear, but most are caused by viral infections and inhaled allergens. Airway inflammation has been reported not only after intense exercise, but also during resting among endurance athletes, swimmers and cross-country skiers.

Some studies were not able to identify pathogens causing a URTI. The unidentified URTIs were reported as being shorter in duration and lower in severity compared to infectious URTIs. As a result of the high amount of assessments that had an ‘unidentified’ cause, this led to the exploration of inflammation not associated with infection among athletes. 

Similar symptoms (e.g., sore throat, fatigue, headache, runny nose, etc.) of URTIs can also be the result of inflammation caused by inhaling cold, dry or polluted air (i.e., climate conditions), stress on the airways or dehydration, which occur because of the decrease in the integrity of the respiratory cell membranes. 

Numerous studies have reported aeroallergen sensitivity in 20-40% of athletes, which resulted in allergic rhinoconjunctivitis (i.e., a condition with nasal congestion, runny nose, post-nasal drip, sneezing, red eyes and/or itchy nose/eyes). Other studies found a 40-50% prevalence of allergic rhinoconjunctivitis among Olympic athletes.

There is a link between training volume and risk of respiratory illness. Training at a high intensity and/or high volume increases susceptibility to infection because of changes in immunity, which include a decrease in salivary IgA and an increase in pro-inflammatory cytokines.

Salivary IgA concentration or excretion rate is used to evaluate the effect of exercise on mucosal protection and associations with URTIs. An increased risk for URTIs for elite athletes is associated with low levels of salivary IgA and/or excretion rates, low pre-season salivary IgA levels and decreasing levels over training. It is suggested that probiotics help increase saliva IgA levels.

URTIs are prevalent among athletes and regardless of what is causing the URTI, their recurrence among athletes can cause fatigue that negatively impacts training and performance. As we will discuss further, probiotics – because of their ability to strengthen immunity and regulate inflammation – are a practical nutritional intervention to prevent or lower the chance of getting a URTI. 

In summary, athletes experience inflammation from: 

1) intense training that disrupts the gut barrier function

2) stressors (e.g., poor sleep, poor diet, alcohol, intense training, etc) that negatively alter the healthy balance of gut microbiota

3) non-infectious causes that impact the respiratory system.

Managing inflammation is critical to optimal recovery and in turn performance. Now let's see how probiotics play a role in this management. 

Probiotics Regulate Inflammation

First and foremost, a balanced gut microbiota is highly important because good gut bacteria can strengthen immunity. A decrease in the prevalence of this good microbiota can lead to the growth of bad bacteria that activate immune cells and suppress important regulatory factors (e.g., decreased synthesis of immunoglobulin A (IgA) and lower levels of important anti-inflammatory cytokines such as IL-10 and TGF-ß). This dysbiosis can lead to chronic inflammation. The science suggests that probiotic supplementation may reverse dysbiosis, return the gut to a healthy gut and bring inflammation under control. 

Probiotics regulate inflammation by:

Maintaining the gut barrier. A weak gut barrier occurs when there are gaps between the cells that line the intestinal wall. These gaps are a critical factor in the initiation of chronic inflammation. Certain molecules that shouldn’t cross the gut barrier (e.g., metabolic waste and undigested food) and bad bacteria (which can release the endotoxin lipopolysaccharide (LPS) from their cell wall) can enter the blood because of increased gut wall permeability. This is referred to as “leaky gut” and causes endotoxemia, which is pro-inflammatory. The continual release of LPS in the blood leads to low-grade inflammation. Treatment of low-level endotoxemia focuses on repairing the permeability of the gut barrier (i.e., strengthening it). Certain probiotic strains can enhance the integrity and function of the gut barrier by:

  • Strengthening the physical barrier. Some probiotic strains can reduce the pro-inflammatory cytokine tumor necrosis factor alpha (TNF-alpha), which causes a leaky gut.
  • Increasing mucin production. The mucosal immune system functions as a barrier and it protects the mucosal layer of the GI, urogenital and respiratory tracts. Probiotics can impact the development and maintenance of the mucosal layer.
  • Producing antimicrobial peptides. These small peptides are a primary defense on mucosal surfaces, especially for alleviating acute inflammation. Certain probiotics are considered powerful activators for producing and regulating antimicrobial peptides.
  • Alleviating the effects of bad bacteria. Probiotics can outcompete the bad bacteria to help maintain the gut barrier.

Increasing the production of short chain fatty acids (SCFAs). Bacteria produce SCFAs when they digest non-digestible carbohydrate (i.e., certain types of fiber). Of the SCFAs, butyrate is important in regulating inflammation because of its anti-inflammatory effects. Butyrate behaves as a:

  • Signaling molecule by blocking pathways that release pro-inflammatory cytokines
  • Regulator for the production of certain cytokines by affecting their ability to travel to sites of inflammation
  • Main source of energy for gut cells, which helps maintain the gut barrier
  • Attaching to immune system receptors to stimulate pathways that release cytokines associated with inflammation.

Not all probiotic strains have the same effects on different signaling pathways, but some can attach to immune system receptors and help certain pathways involved in maintaining the balance in the mucosal layer between pro-inflammatory and anti-inflammatory responses. This influences inflammation by enhancing the production of suppressive and regulatory cytokines.  

Don’t let chronic inflammation hold you back from training and competing. Optimal recovery begins with preparation through probiotic supplementation that will shut down stressors on the gut, which contribute to chronic inflammation and impede performance. 

by Katie Mark, MS

Katie Mark is currently a Master of Public Health candidate at Tufts University School of Medicine. She is a road cyclist working toward becoming a registered dietitian.


When being an athlete isn't so healthy


As an endurance athlete, you are constantly pushing yourself to the next level. While many of your friends and coworkers are still in bed, you are on the road or in the water working to squeeze in that extra mile or two of training in hopes of shaving even a fraction of a second off of your time on race day. Unfortunately, you may have noticed that your physically demanding lifestyle has started to affect your health. You may have also wondered why it seems so many elite athletes drop out of races from “infections.” There is a scientific reason why athletes are more susceptible to illness. Below we will explore the reasons for this and what you can do to stay healthy so you can keep on striving for greatness.

Whether you are biking, swimming, or running, the harder you train, the higher your risk for infections. One study found that elite triathletes and cyclists have a higher incidence of upper respiratory infections (URIs), with the common cold being the most frequent. Additionally, research suggests that this increased risk for URIs may be due to a weakened immune system in athletes.

Why do endurance athletes have impaired immune function? If you read our article, “What Athletes Need to Know About Leaky Gut”, you may remember that intestinal permeability increases with exercise intensity. This increased permeability may cause substances to “leak” from the gut into the bloodstream, a process called endotoxemia, and weaken your immune system. While the exact mechanism is currently being investigated, prolonged exercise has also been found to lower the levels of immune cells.

Does this mean you have to choose between your health and your training? No way! Along with proper hydration, sleep, and optimal nutrition there are ways to help prevent the potential side-effects of intense training. Probiotics have been shown to boost the immune system and are a fantastic tool to add to your training repertoire. Specifically, probiotics reduce the frequency of URIs in endurance athletes and increase markers for immune system function. Are URIs not an issue for you? Probiotics have also been found to reduce exercise-induced gastrointestinal (GI) symptoms.

As an endurance athlete you need to optimize every element of your training, on the road as well as off. Bottom line: stay healthy – finish strong!

by Katelyn Collins

Katelyn Collins, is a future registered dietitian with a passion for probiotics, a knack for nutrition communications, and a love of athletic pursuits on both land and sea.


What athletes should know about leaky gut


You have probably heard the term "leaky gut" before, but what does the science actually say  about this phenomenon and how does it relate to endurance athletes?

When we talk about leaky gut, we are really referring to an increase in intestinal permeability. This does not mean that there are holes in the intestines, but rather that the spaces between the cells that make up the intestinal lining have widened. Normally, intestinal cells are closely packed next to each other to form tight junctions that only let small molecules pass from the intestines into the bloodstream. During times of increased permeability, the tight junctions loosen giving larger molecules and toxins the opportunity to leak into the bloodstream.

Increased intestinal permeability is a particularly important issue for endurance athletes because exercise has been shown to draw blood flow away from the gut which increases permeability and may lower the efficacy of the immune system. This can lead to common side effects that many endurance experience such as cramps, diarrhea, nausea, and an increased risk of infection. One study found that permeability increases with running intensity so the harder you train, the higher your risk for these adverse effects. But don’t worry, no one is telling you to lighten up on your training! There is actually a way to help prevent the exercise-induced increase in permeability: probiotics.

Probiotics have been shown to prevent intestinal permeability and even prevent exercise-induced permeability specifically. The idea is that probiotics form a protective barrier around the intestinal cells which reduces permeability and supports the immune system. This may explain why probiotic supplementation is associated with fewer gastrointestinal and respiratory illnesses in athletes.

Probiotic supplements are a great tool to help you stay healthy while training hard, but be sure to choose your probiotic wisely. If you read our post on why probiotic strains matter, you will remember that a probiotic should contain the types that have been shown to result in the benefits you are looking for you.

by Katelyn Collins

Katelyn Collins, is a future registered dietitian with a passion for probiotics, a knack for nutrition communications, and a love of athletic pursuits on both land and sea.


It's All About the Strains


Would you use a pack of chihuahuas to pull your dog sled or give your grandmother a Saint Bernard as a lap dog? Even though all dogs are from the same species and subspecies, Canis lupus familiaris, their traits and behaviors vary by breed. Similarly, even though bacteria from the same species may share certain characteristics, their functions can vary by strain.

When you buy a bottle of probiotics, the genus and the species are used to identify the different types of bacteria in the product. For example, in Lactobacillus acidophilus, Lactobacillus is the genus and acidophilus is the species. Some companies also include the strain at the end of the name. The strain may appear as letters (Lactobacillus rhamnosus GG), numbers (Bifidobacterium infantis 35624), or a combination. There is no standardized format for strain naming, so you may even see the company name within the strain name. Regardless of the naming system used, strains help us distinguish between benign, helpful, or harmful bacteria from the same species.

Probiotics are often called “beneficial bacteria” because these particular species provide a helpful service for us. When research is performed on probiotics to investigate the positive effects, only one strain of a particular species is tested. Lactobacillus rhamnosus GG is an extensively studied bacterial strain that has been shown to reduce diarrhea and shorten the duration of GI-symptom episodes in marathon trainees. But just because one strain of Lactobacillus rhamnosus shows a therapeutic effect, does not mean that all strains of this species will have the same benefit.

When purchasing probiotics, it’s essential to identify what you hope to achieve by taking them and then select a probiotic that uses strains that have been shown to provide the benefits you are looking for. If you are searching for a probiotic supplement to support your endurance racing, as I assume you are, then you've found the right place

by Katelyn Collins

Katelyn Collins, is a future registered dietitian with a passion for probiotics, a knack for nutrition communications, and a love of athletic pursuits on both land and sea.


Prebiotics and Probiotics: The Perfect Pair


You may have noticed that some probiotic supplements contain “prebiotics”, but what are prebiotics exactly and what do they have to do with probiotics?

Prebiotics are a type of fiber that resist digestion. Instead of being broken down by acids or enzymes in our digestive tracts, prebiotics pass through intact and are fermented by the beneficial bacteria that live in our large intestine. This fermentation process produces short chain fatty acids (such as butyrate) which support normal intestinal function and inhibit growth of pathogens.

Prebiotics occur naturally in a variety of foods and are often isolated and added to products to increase their fiber content. Some common prebiotics are fructo-oligosaccharides (FOS) from agave, inulin from chicory root, beta-glucans from oats and baker’s yeast, and resistant starch from potatoes.

You may have seen one or more of the above ingredients included in a probiotic supplement. This is because probiotics are living organisms that need nourishment in order grow and function properly. When you take a probiotic supplement, the probiotic organisms will consume the prebiotic which will allow them to colonize the large intestine and carry out their valuable functions. Simply put, prebiotics feed probiotics.

When shopping for a probiotic, be sure to keep the type of prebiotic in mind. Fructo-oligosaccharides (FOS) are commonly found in probiotic supplements, but they may cause negative side effects in some people. FOS has been found to cause digestive disturbances, especially flatulence and bloating. If you have ever been doubled over in pain after an excessive amount of onions, you have experienced the effects of too much FOS.

Since GI complaints are so common among athletes we wanted to avoid these potential side effects. Instead, Sound Probiotics contain the prebiotic beta-glucan which has been shown to increase the performance of various probiotics. Additionally, beta-glucans have been found to decrease upper respiratory infection severity and duration and may even prevent respiratory symptoms following a marathon.

Clearly, prebiotics are necessary to optimize the benefits of probiotic supplements, but not all prebiotics are the same. Beta-glucans are effective prebiotics that also have the added benefit of boosting the immune system like the probiotics they support.

by Katelyn Collins

Katelyn Collins, is a future registered dietitian with a passion for probiotics, a knack for nutrition communications, and a love of athletic pursuits on both land and sea.