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.