Our immunity is often a forgotten part of our nutrition plan for optimal recovery. Intense exercise weakens our immunity because of the impact on our gut – an organ that is 70% of our immune system. A weakened gut leads to an open window for opportunistic, bad bacteria to invade and cause infection. This susceptibility can disrupt training – which can decrease sport performance – or require withdrawal from a competition. 

Fortunately, good gut microbiota can help make sure your hours of investment in training are worthwhile. Some gut microbes work with our gut and immune cells to take care of disturbances to immunity that result from high levels of physical and environmental stress.

In this blog, we’ll discuss:

  • The relationship between immunity, the gut and microbiota
  • How probiotics strengthen immunity
  • The negative effects of intense exercise on our gut
  • The effects of probiotic supplementation in athletes 

Athletes undergoing endurance training balance a fine line between enhancing health through exercise and hurting it. Exercise places physical stress on the gut, which lowers immunity. This is inevitable, but probiotics may be a simple nutritional intervention to fight the stress. 

The Relationship Between the Immunity, the Gut and Microbiota

The gastrointestinal (GI) tract is the most important part of our body’s defense system – especially because it’s 70% of our immunity. The intestine has the most lymphoid tissue – the lymphatic system is part of the circulatory system and a critical part of the immune system. These are important components of the gut: 

Mucous layer. The first-line-of-defense against invading pathogens the thick mucous layer (i.e., the innermost layer of the GI tract that is only one cell thick) surrounding the lumen (i.e., open space within the gut). It has two major functions. First, it needs to absorb nutrients. Second, it needs to guard against infectious, opportunistic pathogens because this intestinal barrier separates bacteria from our gut epithelium (i.e., a layer of cells that absorbs healthful substances and provides a barrier against bad substances). Mucus inhibits bad bacteria from colonizing by trapping and removing them so that they don’t enter our internal circulation. 

The mucosal layer comes in direct contact with digested food, which has antigens, and microorganisms in the gut lumen so it has many anti-microbial factors such as immunoglobulin (Ig)A, defensins, mucins and enzymes. IgA is needed to protect the mucosal surface. The secretion of IgA antibodies in the gut can lead to an immune response that affects the immune response at other mucosal surfaces in the body, such as within the respiratory tract.

Dysregulation, or complications, with the mucosal immune system underlies many inflammatory illnesses (e.g., ulcerative colitis, celiac disease) and increases susceptibility to cancer and infections. Essentially, it’s the anti-microbial proteins and secretory immunoglobulins that enhance the mucosal layer as a protective layer.

Gut epithelium. The epithelial layer spans the inner surface of the intestine. Cell junctions (proteins) connect epithelial cells. Of these junctions, tight junctions provide the most important physical barrier that is selective in what is allowed in and out (e.g., ions and small molecules). Aside from a physical barrier, it also facilitates communication between luminal contents and gut-associated lymphoid tissue (explained below). These cells have Toll-like Receptors (TLRs) that can recognize the good and bad bacteria and the toxic products of bad bacteria. When the TLRs recognize the pathogens, the epithelial cells attack the pathogens with an immune response. The role of probiotics is to regulate GI tract immunity by communicating with different receptors on the epithelium.

Gut-associated lymphoid tissue (GALT). The GI immune system is usually referred to as GALT, which protects the body from invasion. GALT is organized in structures called Peyer’s patches, which act like immune sensors (i.e., surveillance cameras). GALT stores immune cells (e.g., T helper cells and B lymphocytes) that attack and defend from pathogens. M cells cover the Peyer’s patches and coordinate immune defense. They take antigens and bad bacteria from the gut to certain immune cells that either activate or inhibit an immune response. Under the epithelial layer, dendritic cells (DCs) can either ignore or respond to invading antigens and bacteria.6 DCs can tell T-cells to release pro- or anti-inflammatory cytokines (i.e., proteins used in cell signaling, especially important in the immune system). 

A healthy immune system is maintained by the extensive, friendly interaction between gut microbiota and our mucosal immune system. When there’s an unhealthy gut environment, the mucin barrier weakens. This allows microbes to invade the epithelium and – ultimately – cause inflammation.  Essentially, our immune system needs to have an appropriate balance between tolerating good gut microbiota and defending against bad bacteria.

Factors in athletic training and competition that affect immune function

Factors in athletic training and competition that affect immune function

Probiotic Action to Strengthen Immunity

Maintaining the gut barrier is critical, especially in response to the consequences of intense exercise (explained below). Probiotic actions that modify and modulate different parts of the gut help strengthen the gut. Here’s how good gut bacteria strengthen our immunity:

Enhance the gut barrier. This is one of most important benefits. Probiotics can regulate the number of tight junction proteins between cells and can prevent or reverse the consequences of the bad bacteria. Many probiotic strains such as Lactobacillus plantarum, Bifidobacterium longum and L. rhamnosus positively impact tight junctions and intestinal barrier function. Reducing gut inflammation by reducing cytokine and reactive oxygen species (ROS) production also strengthens the barrier. 

The protein zonulin, released from the liver and gut, regulates the open spaces between cells of the gut (i.e., tight junctions between cells) and serves as a biomarker to estimate intestinal barrier integrity. Normal functioning allows nutrients and other molecules to enter and leave the gut. However, leaky gut causes the spaces between cells to open too much, which allows protein molecules to enter the blood and potentially causes an immune reaction. Not only that, other substances in the gut, such as bacteria, can enter, which creates inflammation and makes the liver work harder to get rid of the unwanted products.

Higher amounts of zonulin means changes in tight junction integrity and increased GI permeability. Zonulin is considered an acceptable biomarker to evaluate exercise-induced intestinal barrier disturbances, as evidenced by higher zonulin levels in the feces of humans,30 including athletes. The two main triggers activating zonulin are gut bacteria and gluten. 

Measuring zonulin in feces or blood serum is feasible, which makes it practical for athletes to test so that they can evaluate whether or not they need a dietary intervention. Decreased gut barrier function is triggered by changes in zonulin-activating gut microbiota, which can lead to inflammation. 

A randomized, double-blinded placebo-controlled trial investigated probiotic supplementation on biomarkers of intestinal barrier, oxidation and inflammation in 23 trained men following rest and intense exercise. The men either received a supplement containing six probiotic strains (B. bifidum, B. lactis, Enterococcus faecium, L. acidophilus, L. brevis, and L. lactis at 1 billion CFU/day) or placebo one hour before a meal for 14 weeks. 

Breakfast was the same for each participant before each exercise test to prevent differences in nutrients. Participants were not allowed to exercise three days before any exercise test. The men used an exercise bike to complete an intensive 90-minute exercise at the beginning of the experiment and after 14 weeks.

The results:

  • Average concentrations of zonulin at baseline were slightly above normal for both groups
  • Following 14 weeks of supplementation, the probiotic supplement significantly decreased zonulin levels by >20% compared to placebo

The decrease in zonulin went from slightly above normal at baseline (<30 ng/mL) to normal range following 14 weeks. It was suggested that the subjects might have had a slight increase in intestinal permeability at baseline, which could have resulted due to intense exercise training. It was concluded that appropriate probiotic supplementation may improve intestinal barrier function. 

The reason for improved intestinal barrier function is suggested to be the result of probiotics that can activate a particular TLR, which can improve epithelial resistance. Also, the probiotics may have outcompeted and/or replaced the zonulin-activating bacteria.  

Other effective strains with positive impacts on intestinal barrier function include B. infantisL. plantarumB. longum and L. rhamnosus.

Stop pathogenic bacteria. Probiotics can enhance host resistance by creating ecological niches in the mucosal layer to prevent pathogens from colonizing these surfaces. They do this by limiting the surface area for pathogenic bacteria to attach, decreasing nutrient availability for pathogens and secreting antimicrobial substances, such as short-chain fatty acids (SCFAs) – produced by bacteria when they digest non-digestible carbohydrate. SCFAs increase mucin production and increase the acidity of the gut, which stops the growth of bad bacteria and strengthens the gut barrier. 

Increase mucin production. Probiotics can strengthen the first line of defense – the mucosal layer. Probiotics, such as Lactobacillus, have been shown to influence mucin production.

Engage with immune cells. Immune cells (e.g., M cells, DCs) are constantly communicating with gut bacteria. Probiotics are taken up by M cells to engage with DCs and epithelial cells that activate responses when they take antigens to T helper cells (i.e., cells that help other immune cell activity by releasing cytokines that can regulate immune responses). Probiotics, such as L. plantarum and L. paracasei, can activate DCs, with L. paracasei being more immunomodulatory. Some strains can improve immune function by increasing the number of cells producing IgA and the amount of Th1 helper cells and natural killer T cells.

Aside from the GI tract, probiotics can strengthen immunity by their interaction with the common mucosal immune system, which links different parts of the GI tract (e.g., Peyer’s patches) to different sites within the GI tract and other mucosal surfaces, including the upper respiratory tract and genito-urinary tract.

Essentially, probiotics have a friendly relationship with the gut because they communicate with different parts of the gut immune system, maintain the gut barrier and prevent bad bacteria from colonizing. 

The Effects of Intense Exercise on the Gut

High-intensity exercise is immunosuppressive. Immune changes at the cellular level include a reduction in white blood cell function, which creates a window of opportunity for bad bacteria. Cortisol levels also increase as intense exercise is prolonged.

Intense exercise can also cause an acute inflammatory response by increasing the amount of pro-inflammatory cytokines (e.g., TNF-alpha, IL-1, IL-6, IL-1, TNF receptors) and anti-inflammatory regulators (e.g., IL-10, IL-8).

Disturbances that Lead to Leaky Gut and Endotoxemia

The primary impact that weakens our intestinal wall barrier is the change in blood flow from the gut to skeletal muscle and the heart. This effect of changed blood flow is greater with higher intensity and prolonged exercise. Subsequently, the gut receives less:

  • Blood
  • Oxygen
  • Nutrients
  • Removal of metabolites

This hurts gut cells. In fact, GI complications are the consequence of blood moving away from the gut, which leads to abdominal cramps and diarrhea – major complaints experienced in endurance sports.  

A big increase in ROS also results from intense exercise, which leads to oxidation, cell communication changes and inflammation because of the cytokines released from the GALT immune cells. This leads to changes in the tight junction proteins and epithelial cell membranes – thus, lowering immunity. 

Water availability in the gut is another complication from intense exercise. The change in osmolality (i.e., chemical particles in the fluid component of blood) and gut movement may decrease the strength of the intestinal barrier. Increased gut barrier permeability is especially apparent in those exercising for a long time in the heat.

Reduced tight junction integrity between cells leads to a ‘leak’ that allows pathogens/toxins to pass easily through the intestine. The immune system responds to this leak, which results in inflammation and oxidative stress and a condition called endotoxemia. 

Endotoxemia is when endotoxins (i.e., a toxin in bacteria and released when the bacterial cell wall is destroyed) are in the blood. Lipopolysaccharide (LPS) – a major component of the outer membrane of certain bacteria – is an endotoxin of concern because it causes a strong immune response from a host. 

Blood flow away from the gut, ROS, water availability and exercising in the heat decrease the strength of the gut barrier, which increases gut permeability and leads to endotoxemia. This ‘leaky gut’ lowers the gut barrier’s protective function.


The Consequences of a Weakened Gut Barrier

GI permeability (i.e., weakened gut barrier) increases following running on a treadmill at 80% VO2max (i.e., intense exercise), yet not at 40 or 60% VO2max. A leaky gut increases our susceptibility to infections and autoimmune diseases because of increased absorption of pathogens/toxins into the blood and tissues. 

Increased gut permeability – because of exercise – that results in endotoxemia was found in highly trained male triathletes. One study investigated whether or not GI complaints during ultra-endurance exercise was related blood moving away from the gut during exercise, which causes endotoxemia. Blood samples were taken from 29 athletes before, immediately after, and 1, 2 and 16 h following a long-distance triathlon to evaluate levels of LPS and cytokine production, such as the pro-inflammatory interleukin-6 (IL-6). 

GI symptoms were found in 93% of participants and 45% reported severe GI distress. Mild endotoxemia was found in 68% of the athletes immediately following the race. There was an increase of IL-6 (27x the original level) immediately after the race, which led to an acute-phase response of increase in C-reactive protein 16 h after the race. Ultimately, the researchers concluded that GI complaints in ultra-endurance athletes may have resulted from endotoxemia (LPS leakage) and increased cytokine levels. 

Effects of Probiotic Supplementation in Athletes:

The immunological effects of probiotic supplementation in athletes are promising. During stressful periods of training and competition, probiotics may:

Reverse T-Cell Defect

A study explored the effect of L. acidophilus (2 x 10*10 CFUs taken daily for four weeks) on immunity in 27 healthy and fatigued athletes. The fatigued athletes had a much lower level of IFNγ (i.e., a cytokine needed for immunity and produced by T cells) than the healthy athletes, which suggested a T cell defect. Following one month of supplementation, the fatigued athletes increased their IFNγ to the same level as the healthy athletes. These results were considered important because T-cells are critical in maintaining immunity and probiotic supplementation showed to reverse the T-cell defect. 

Lower Risk for Upper Respiratory Tract Infections

Higher exercise intensity as well as other stressors increase the risk of infection in athletes

Higher exercise intensity as well as other stressors increase the risk of infection in athletes

The immunosuppressive effect of exercise increases an athlete’s susceptibility to develop upper respiratory illness (URTI) (e.g., the common cold). Many athletes, especially elite athletes in rowing, cycling, swimming and triathlon, undertake prolonged intense exercise and are at increased risk for URTI resulting from intense training and competition.

URTIs are most common during the winter and adults usually have 2 to 4 URTIs per year. Increased risk for URTI could result from exercise-induced disturbances in immunity that gives opportunistic pathogens ability to cause infection. This is made worse when breathing cold, dry or polluted air. 

As previously mentioned, IgA is needed to help protect mucosal barriers. A study using 38 elite athletes from America’s Cup yacht race explored the effect of 50 weeks of training and competition on salivary IgA to determine if it was a risk factor for URTIs. Each week, samples of saliva were taken 38 h after exercise along with URTI, training load and perceived fatigue rating. The study found a decrease in salivary IgA over 3 weeks before an URTI along with a an increase of salivary IgA by week two following an URTI, which suggested lower salivary IgA increased the risk for a URTI. 

Strenuous exercise increases the amount of URTI in athletes. The increased risk for URTI during heavy training or following a marathon race was found in a study investigating the incidence of URTI of 2,311 runners in the week following the 1987 Olympic marathon.  

A 2015 meta-analysis investigated studies involving 3451 athletes and non-athletes and concluded that there may be a benefit to taking a daily probiotics supplement to reduce the symptoms of URTI.

Many other studies using athletes suggest that daily probiotics supplementation may lead to fewer days and severity of URTI. A study investigated a probiotics supplement during four months of winter endurance training in 84 men and women on URTIs and immunity. The highly active participants were randomized to either the probiotic (L. casei) or placebo daily for 16 weeks. Weekly trainings and illnesses were recorded. 

The results:

  • Athletes on probiotics supplementation were 36% less likely to experience 1 or more weeks with URTI symptoms compared to placebo
  • Number of URTIs was significantly higher in the placebo group than probiotics group
  • Probiotic group had higher levels of salivary IgA

Ultimately, habitual intake of the probiotics supplement may be helpful in reducing the number of URTIs in athletes. This could have been due to higher levels of saliva IgA, which the study suggests that probiotic supplementation helped maintain saliva IgA levels during a winter season of training and competition.

A double-blind, placebo-controlled cross-over study investigated the effect of L. fermentum supplementation for 28 days (1.2 x 1010 CFU per day) to improve the mucosal immune system of 20 elite male distance runners.41 The study assessed treadmill performance, immunity, training and illness. Cytokine levels, salivary IgA levels and duration and severity of respiratory tract infections were measured. 

L. fermentum decreased the number of days athletes had respiratory illness, which was suggested to be the result of improving T-cell function. 

Reduce GI Illness Symptoms & Duration

A study explored the effect of probiotic supplementation (109 CFU of L. fermentum) on GI illness symptoms and immunity using 99 competitive cyclists – men and women. Subjects were randomized to consume either one daily probiotic supplementation or placebo for 11 weeks during the winter. Participants recorded any symptoms of GI illness daily. To measure systemic immunity, blood samples were taken pre- and immediately post-exercise to determine cytokine concentrations. This was performed at the beginning and end of supplementation. To measure mucosal immunity, saliva samples were taken pre- and post-supplementation to measure salivary IgA concentrations. 

It was suggested that a 20-60% decrease in cytokine changes associated with probiotic supplementation could suggest enhanced immunoregulation. However, The study did not find a considerable relationship between cytokine changes – caused by exercise – and illness symptoms following supplementation. However, there was a major reduction in respiratory and GI symptoms after 77 days of supplementation for males, but not females. 

Another study investigated the effects of L. rhamnosus supplementation or placebo in 141 runners for three months before a marathon. The was no significant difference in the number of respiratory or GI illnesses two weeks after the marathon. However, the probiotic group had a shorter duration of GI symptoms, 2.9 days for the probiotic group versus 4.3 days for the placebo group. 

Counteract the Stress of Exercising in the Heat

A double blind crossover study used 10 male runners to evaluate if four weeks of daily probiotic supplementation (45 billion CFU of Lactobacillus, Bifidobacterium and Streptococcus strains, including L. acidophilus, L. rhamnosus, L. casei, L. plantarum, L. fermentum, B. lactis, and B. bifidum) or placebo would impact GI permeability while exercising in the heat. It is suggested that hyperthermia reduces the integrity of gut epithelial cells. The runners exercised to exhaustion at 80% of their VO2max at 95F and 40% humidity.

The results for probiotics supplementation:

  • Increased run time to exhaustion in the heat compared to placebo (37 min 44 sec vs. 33 min)
  • A small to moderate reduction in markers of GI permeability compared to placebo 

It was suggested that gut barrier integrity or immunomodulatory effects after probiotic supplementation may have improved performance, but ultimately, the mechanism was unclear. 

Probiotics: Immunonutrition for Sport Performance

Training is a stressor, and our bodies need to recover from this stress. High training volume and intensity without adequate recovery means the stress stays, which puts athletes at an increased risk for a weaker immunity and illness. Recovery from intense training requires an immunological aspect of sports nutrition: improving the intestinal barrier to reduce the athlete’s susceptibility to endotoxemia and cytokine production. In fact, current recommendations for immune-nutrition support in athletes includes taking a daily probiotic supplement that has at least 10 billion CFU. 

Probiotics help maintain the gut barrier, which strengthens immunity and leads to a secondary health benefit related to performance. Improved sport performance results from the ability to train harder and show up to competitions because you aren’t sidelined with an illness. Probiotics are a nutritional strategy to optimize recovery, which may limit illnesses affecting 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.


The Performance-Enhancing Gut


Preparation involves more than having top of the line gear. If you’re going to be the best you need to optimize every element of your training. What you put in your body serves as the foundation for your performance. Probiotics reinforce that foundation ensuring you are ready to go on game day.

The 4 Keys to the Performance-Enhancing Gut:

1. Improved immune function: Athletes are more susceptible to impaired immune function, and subsequent illness, due to the shear amount and intensity of their training and competition. Probiotics can prevent illness in athletes in  several ways:

Physical barrier - L. fermentum and L. plantarum have been shown to increase the production of mucin, which is a substance produced in the gut that inhibits the bad bacteria from attaching to the intestinal wall. Lactobacillus and Bifidobacterium have also been shown to reduce GI permeability (“leaky gut”) which occurs during times of intense exercise and heat and can lead to impaired immune function and poor recovery as well. 

Cellular changes - probiotics stimulate anti-inflammatory proteins. 

Systemic immunity -  probiotics can increase the number and activity of cells that fight off infection.

2. Maintenance of optimal glucose levels

The gut microbiota ferments complex carbohydrates into short chain fatty acids (butyrate, acetate, and propionate). The type and amount of SCFAs produced depends on our age, diet (e.g., availability of prebiotics), composition of gut microbiota, gut transit time and pH of the colon. The probiotic bacteria that produce SCFAs include:

  • Bifidobacterium
  • Lactobacillus
  • Faecalibacterium
  • Ruminococcus
  • Bacteroides

The SCFAs, propionate and acetate serve as fuel sources for the liver and muscle tissue, allowing for the maintenance of optimal glucose levels to meet the body’s demands during exercise. 

3. Reduce inflammation thereby reducing fatigue

Probiotics can reduce inflammation in several ways. One mechanism was evaluated in a study performed with runners taking a probiotic with Lactobacillus and Bifidobacterium strains. The researchers found the runners had reduced inflammatory markers following running in heat. In turn, these runners were able to run longer in the heat without becoming fatigued. 

Another mechanism that has been studied involves the fact that intense exercise generates a high amount of reactive oxygen species (ROS) (i.e., free radicals), especially during exhaustive and long-lasting exercise. Subsequently, the intense exercise and increased oxygen consumption (which also leads to oxidative stress) results in athletes with greater amounts of ROS circulating in their body. 

Probiotics can fight ROS by stimulating antioxidant activity, which can facilitate better recovery from oxidative stress. In turn, it would appear that probiotics, through their antioxidant activity, have the ability to augment recovery from intense exercise. 

4. Nutrient production and absorption

Various bacterial strains improve our nutrition status by aiding digestion, enhancing absorption and synthesizing nutrients. Certain probiotics can:

  • Synthesize some B vitamins and vitamin K
  • Increase absorption of calcium, iron and vitamin D 
  • Enhance dietary nitrate conversion to the vasodilator nitric oxide (e.g., beetroot juice)

By enhancing nutrient production and absorption, probiotics are important players that bring together nutrition, gut health and human performance. 

The gut is as vital to your performance as any other organ system. Whether it is reducing GI symptoms or improving nutrient production and absorption, taking care of your gut with proper nutrition and probiotics will ensure your best on game day. 


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A Nutritional Intervention for Performance


Probiotics are touted for strengthening immunity and maintaining a healthy gut, but one of the less emphasized health benefits is their positive impact on nutrition. Athletes are prone to flirting with certain nutrient deficiencies because of exercise demands and – sometimes – less than optimal nutrient intake. Research suggests taking probiotics is an attractive dietary intervention to optimize nutritional intake.

Gut bacteria receive their nutrition for energy and growth from our intake of carbohydrate, protein and fat. While breaking down food, bacteria release different by-products that subsequently impact our health and metabolism – most importantly, short-chain fatty acids (SCFAs). Here we provide the evidence-based research on probiotics and how they impact our digestion and absorption of nutrients and how SCFAs enhance our health.

  • Synthesize some B vitamins and vitamin K
  • Increase absorption of calcium, iron and vitamin D 
  • Alleviate symptoms lactose intolerance
  • Enhance dietary nitrate conversion to the vasodilator nitric oxide (e.g., beetroot juice)
  • Increase antioxidant activity
  • Lower cholesterol

Gut bacteria receive their nutrition for energy and growth from our intake of carbohydrate, protein and fat. While breaking down food, bacteria release different by-products that subsequently impact our health and metabolism – most importantly, short-chain fatty acids (SCFAs).

Vitamin-Producing Probiotics

We must obtain most vitamins through our diet because we can’t make them, but deficiencies still occur because of inadequate food intake and unhealthful or unbalanced eating habits. Some vitamin-producing probiotic strains serve as a natural alternative to increase vitamin stores of some B vitamins and vitamin K.

B vitamins are found in many foods, but they can easily be destroyed during cooking and food processing. Vitamin K is found in two forms: phylloquinone (K1) – the main dietary form found in plants – and menaquinone (K2) – synthesized by beneficial gut bacteria and found in meat, dairy and fermented foods. 

Riboflavin (Vitamin B2)

Riboflavin is essential in cellular metabolism, and it can be found in dairy products, meat and eggs. However, riboflavin deficiency still occurs, and exploiting certain bacterial strains that are riboflavin-producers is suggested for the fermented food industry.

A study explored the riboflavin-producing strains in different fermented milk products and found that Lactobacillus fermentum was efficient at producing riboflavin. Another study found that L. lactis produced riboflavin and was able to reduce the physiological consequences of riboflavin deficiency; however, this study was conducted in rats.

Folate (Vitamin B9)

Folate is involved in DNA replication and repair as well as synthesis of nucleotides, vitamins and some amino acids. Folate deficiency can lead to megaloblastic anemia (the number of red blood cells is lower than normal), neural tube defects (especially in pregnant women) and increased risk for heart disease because of elevated homocysteine levels. Certain strains of Bifidobacteria have demonstrated folate biosynthetic properties. The high level folate-producing strains include B. bifidum and B. longum

Strozzi and Mogna conducted a pilot study using 23 healthy volunteers to evaluate the ability of three different Bifidobacteria strains to produce folate. The subjects were randomly assigned to one of three treatment groups with the specific probiotic strain at a dose of 5 x 10*9 colony forming units (CFU) per day. Fecal samples were collected from subjects for two consecutive days before treatment with probiotics and two consecutive days after 30-days of treatment. Subjects were instructed not to consume fermented dairy products containing Bifidobacteria – to prevent ingesting other sources containing Bifidobacteria. The study found that the three Bifidobacteria strains colonized the GI tract and produced significant amounts of folate. 

Vitamin K

Even though our intake of green plants provides vitamin K, a deficiency can result from an out of balance gut microbiome. This may result from pathogenic bacteria that overtake the good bacteria or after antibiotic usage. We can’t store vitamin K so we need to have the right amount of good bacteria to make vitamin K. 

The amount of vitamin K produced by gut bacteria ranges from 10-50%. However, not all gut bacteria produce vitamin K. L. lactis has shown to produce high amounts of vitamin K, an amount that could even serve as a dietary supplement. Yet, the research on absorption and metabolism of bacterially produced vitamin K has not increased in the last two decades. We do know that maintaining a balanced gut microbiota will help ensure we’re getting vitamin K. 

Increase Calcium Absorption

Calcium is one micronutrient that tends to be low among athletes. Athletes are at risk for developing calcium deficiency for many reasons. Calcium from food isn’t always absorbed, and the amount and bioavailability varies among foods. Some food components, such as oxalic acid (found in spinach) and phytates (i.e., an indigestible form of phosphorous – found in grains) can inhibit calcium absorption. 

Also, exercise may increase calcium losses. A study found in nine male competitive cyclists that 10 weeks of intense endurance training increased urinary calcium excretion and lowered serum calcium levels, but these consequences were reversed after the tapering phase. Therefore, high intensity exercise may increase calcium excretion.

A study investigated calcium absorption and bioavailability from calcium-fortified soymilk containing seven strains of Lactobacillus, including L. acidophilus, L. plantarum L. casei and L. fermentum. The highest increase in calcium solubility after 24 hours came from L. acidophilus (89.3%) and L. casei (87.0%). The study concluded that some Lactobacillus species may improve calcium bioavailability.

Probiotics (such as the ones mentioned above) that have the enzyme phytase – which humans lack – may increase the bioavailability of calcium because they can reduce the amount of phytates that bind to calcium. 

Increase Iron Absorption

Iron supports more than 180 biochemical reactions in the body, including the transport of oxygen. Ischemia – an inefficient supply of blood to an organ or part of the body – during excessive training results in an increased demand for iron. Iron uptake increases through intestinal absorption, but only if there’s adequate dietary iron intake. Intense training can result in an increase in hepcidin (i.e., a protein that is the main regulator for iron absorption), which can block iron absorption and result in iron deficiency. 

Iron deficiency is prevalent among athletes and may affect physical performance. This is especially seen in women of reproductive age, because they have high iron requirements, and among those on plant-based diets because of their intake of non-heme iron (which has a lower bioavailability compared to heme iron found in animal-based foods). 

Ferritin is the main biomarker to evaluate iron deficiency. For healthy female and male athletes >15 years old, the ferritin values are: 

  • Empty: ferritin values <15 mcg/l
  • Low iron stores: 15-30 mcg/l
  • Suggested cut-off: 30 mcg/l

Therapeutic approaches to increase iron levels include a higher intake of foods high in iron or iron supplementation. However, probiotics is a dietary factor that serves as a potential therapy to enhance iron absorption. 

L. plantarum has demonstrated an ability to increase iron absorption by over 100% from oats that have low iron bioavailability (because of the high levels of the phytates).

A recent single blind cross-over study using 22 young, healthy women found L. plantarum increased iron absorption from an iron-fortified drink by 50%. At breakfast for four consecutive days, the women drank either a 200-ml fruit juice with 5 mg of iron alone or an iron-fortified fruit juice with L. plantarum. The probiotic-containing drink had 10*9 CFU in Trial 1 and 10*10 CFU in Trial 2. 

The results:

  • Trial 1: Mean iron absorption from the drink with 109 CFU of L. plantarum was 28.6% compared to 18.5% for the control drink 
  • Trial 2: Mean iron absorption from the drink with 1010 CFU of L. plantarum was 29.1% compared to 20.1% for the control drink

The average iron absorption was 28.8% with L. plantarum when the absorption values for all subjects were combined, which was significantly higher than the iron absorption of 19.3% with the control drink. The study found iron absorption was 50% higher with non-heme iron from a fruit drink with L. plantarum than a similar fruit drink without the probiotic. 

Details of the mechanisms by which probiotics can increase iron absorption are lacking. It is suggested that some Lactobacillus strains can increase the bioavailability of iron because they have the phytase enzyme that can break down phytates during fermentation. Yet, L. plantarum has minimal phytase activity and the amount of phytates was low in the fruit drinks in the study. Enhanced iron absorption may be the result of the strain’s ability to colonize the gut and increase mucin (the main component of the mucus layer that lines the gut) excretion. It is suggested mucins can bind to iron and prevent iron removal. Also, mucin may increase iron uptake because of its effect on iron transport proteins that bring iron into cells. Finally, another possible mechanism may result from the decrease in gut pH because of Lactobacilli growth. This creates a more acidic environment to change the iron (i.e., ferric iron) to a more absorbable form (i.e., ferrous iron). 

Enhance Vitamin D Absorption

Vitamin D is critical for bone health, maintaining phosphate and calcium homeostasis – and maybe for physical performance. Yet, vitamin D levels are very low, with the greatest effects based on geographic location (e.g., northern latitude), season of the year and skin color. Even fortified vitamin D milk is not sufficient enough to prevent vitamin D deficiency for all adults at every time of the year. It is suggested that athletes, compared to the general population, may be more susceptible to vitamin D deficiency, and possibly because of inflammation, muscle damage, increased immune activity and increased protein synthesis.

Before we delve into the research highlighting vitamin D-boosting probiotics, the importance of vitamin D for athletes requires emphasizing complications of vitamin D deficiency and the prevalence of vitamin D deficiency among athletes.

These precursors are transformed in the liver and kidneys to:

  • 25-hydroxyvitamin D (25(OH)D): the inactive storage form
  • 1,25-dihydroxyvitamin D (1,25(OH)2D): the biologically active form under tight regulation in the body

1,25-dihydroxyvitamin D interacts with vitamin D receptors found in every tissue of the body. This includes skeletal muscle, which suggests the important effect vitamin D may have on skeletal muscle. 

The best indicator of vitamin D status is reduced blood levels of 25-hydroxyvitamin D [25(OH)D]. The three categories of vitamin D status based on serum 25(OH)D are:

  • Risk of deficiency: <30 nmol/L
  • Risk of inadequacy: 30-49 nmol/L
  • Sufficiency: 50-125 nmol/L 

Low levels of vitamin D are prevalent in the general population. A low level is also a risk factor for: osteoporosis, cardiovascular disease, type 2 diabetes, and cancer. Vitamin D deficiency is also associated with depression, cognitive decline and neurological complications. More specific to athletic performance, vitamin D deficiency also may break down muscle and result in muscle weakness.  

A few studies have suggested that a lower vitamin D intake may be associated with microbiome changes.,

A 2015 systematic-review and meta-analysis of 23 studies and ~2,300 athletes found that 56% of athletes had inadequate vitamin D levels.

A recent cohort study assessed vitamin D levels in 80 professional NFL players (the Pittsburg Steelers) and its association with race, history of broken bones and staying on the team during the 2011 offseason. 

The results:

  • Mean vitamin D level was 27.4±11.7 ng/mL
  • Significantly lower levels for black players, which was 84% of the team, (25.6±11.3 ng/mL) compared to white players (37.4±8.6 ng/mL)
  • All athletes with vitamin D deficiency (<20 ng/mL) were black
  • 91% of athletes with vitamin D insufficiency (20-32 ng/mL) were black
  • 68.8% of the team had vitamin D levels lower than 32 ng/mL

The associated results:

  • Vitamin D levels were much lower in players who had at least one bone fracture compared to players who had no fractures
  • Players who were cut during the preseason as a result of injury or poor performance had significantly lower vitamin D levels compared to players who stayed for the regular season

Ultimately, athletes with vitamin D levels above 32 ng/mL played in more seasons than athletes with vitamin D deficiency. Vitamin D deficiency and insufficiency were prevalent among football players, especially black players. Those with a lower the vitamin D level had a higher risk for getting cut.

These results suggest the need to optimize vitamin D not just for NFL players, especially black players, but potentially all athletes. To address vitamin D deficiency, probiotics is an attractive nutritional intervention.

Jones, Martoni and Prakash published the first human data on probiotics increasing vitamin D absorption in humans. The randomized controlled trial found the probiotic strain L. reuteri may increase serum 25-hydroxyvitamin D by 25.5%. 

The participants’ two-day dietary intake was measured at weeks 0 and 9 to evaluate calories, lipids, proteins, carbohydrates, vitamin A, retinol, carotenoids, vitamin E and vitamin D. 

The study primarily measured the change in serum low-density lipoprotein-cholesterol (LDL-C) over the nine weeks. Fat-soluble vitamin analysis was conducted for weeks 0 and 9 following the intervention. 

The results:

  • L. reuteri increased serum 25-hydroxyvitamin D by 14.9 nmol/L (25.5%) – a significant difference compared to placebo, which was 17.1 nmol/L (22.4%)
  • No differences in the absorption of other fat-soluble vitamins

Currently, this is the first study to show a probiotic supplement increased vitamin D levels. However, the mechanism is unclear. It may be the result of 1) an increase in vitamin D absorption or 2) greater synthesis of the vitamin D precursor. Yet, influencing the microbiome with the right probiotics signals a feasible approach to increase vitamin D.

Alleviate Symptoms of Lactose Intolerance

Dealing with lactose (i.e., the natural sugar in milk) intolerance as an athlete is frustrating, especially for those who want to use the fluid, protein and carbohydrate in milk or products with whey protein for recovery. Lactose intolerance results from a low amount of the lactose cleaving-enzyme β-galactosidase (i.e., lactase) in the mucosal layer of the small intestine. Secondary causes of lactose malabsorption result from other health complications (which can be reversible) including: 

  • Inflammation of the small intestine
  • Protein-energy malnutrition (i.e., lack of protein)

Probiotics that have high β-galactosidase activity may help those who are lactose intolerant. This is why those who are lactose intolerant may be able to tolerate yogurt because the lactose is already partially broken down.

A randomized controlled trial investigated the effect of L. reuteri supplementation, compared to placebo, on symptoms of lactose intolerance in lactose intolerant people randomly assigned to one of three 20-subject treatment groups: tilactase (e.g., Lactaid) group, placebo group and L. reuteri group. Lactose maldigestion was assessed with the hydrogen breath test and GI distress symptoms. The study found that L. reuteri, compared to placebo, lowered the amount of excreted hydrogen and reduced GI symptoms following lactose intake. 

Microbial β-galactosidase (also found in L. bulgaricus and Streptococcus thermophilus) may be an effective treatment to alleviate lactose intolerance symptom for lactose malabsorbers. In fact, the bacteria don’t need to be alive – just the cell walls need to be intact to protect the enzyme when it passes through the stomach. Lactose digestion may improve because the passage of lactose through the gut is delayed, which allows β-galactosidase more time to breakdown lactose. 

Enhance the Conversion of Nitrate from Beetroot Juice to Nitric Oxide

Beetroot juice is the latest in functional foods for sport performance. The dietary nitrates in beetroot juice convert to nitric oxide (NO), a molecule that widens blood vessels and allows nutrients and oxygen to enter skeletal muscle. NO increases efficiency of oxygen use in muscles during strenuous exercise. The entero-salivary nitrate-nitrite-NO pathway (i.e., GI system) starts with conversion of dietary nitrate to nitrite in the mouth, then the stomach and finally the small intestine. Yet, the link in the conversion of nitrates to NO requires good bacteria throughout the entire GI tract.

Bacteria on the tongue that convert nitrate to NO (by using the enzyme nitrate reductase) can be destroyed by antibacterial mouthwash. Govoni et al. used seven healthy volunteers to investigate what impacts the ability of oral bacteria to metabolize inorganic nitrate to form nitrite and then bioactive NO. Notably, the bacteria in our mouth that convert nitrate to NO were destroyed by antibacterial mouthwash, which led to a lack of NO and no benefits from beetroot juice nitrates. 

Beetroot juice (or other food containing dietary nitrate) is not the only way to generate NO. Our body can produce NO from the amino acid L-arginine and oxygen by using the enzyme nitric oxide synthase. This endogenous way of producing NO greatly impacts the GI tract. 

To address this, a study investigated if specific gut bacteria, in humans and in rats, could produce NO. Fecal samples from eight healthy volunteers were used to measure the NO production by different bacteria. Lactobacilli and Bifidobacteria in human feces generated NO from nitrite, and a few of the bacteria strains generated NO from nitrate. Rats receiving Lactobacilli supplementation with nitrate present produced more NO in the gut than rats with no gut bacteria. 

It’s suggested that some bacteria can capture NO by binding to specific proteins or by using nitrate reductase. Even though the study used rats and more human studies testing different bacterial strains are needed, the results suggest gut bacteria – not just oral bacteria – may have the capacity to generate NO. 

Increase Antioxidant Activity

We use oxygen to harness energy from food, which produces reactive oxygen species (ROS) (i.e., free radicals) and can lead to oxidative stress (an imbalance between oxidant and antioxidant levels). ROS can damage lipids, proteins and nucleic acids in cells. To neutralize ROS, both antioxidants from food and certain enzymes in our body make up the biological antioxidant barrier. 

Intense exercise generates a high amount of ROS, especially during exhaustive and long-lasting exercise. Subsequently, the intense exercise and increased oxygen consumption (which also leads to oxidative stress) results in athletes with greater amounts of ROS circulating in their body. 

Probiotics may be antioxidant suppliers that can facilitate better recovery from oxidative stress. Some studies suggest that certain probiotic strains may provide antioxidant activity and reduce oxidative stress.

The first study to investigate the effect of probiotics on exercise-induced stress used L. rhamnosus and L. paracasei. Male athletes were assigned to either the probiotic group (12 men) that consumed a mix of the two strains (1:1, ~10*9 cells/day) or the control group (12 men) that didn’t receive supplementation. All athletes received a personalized diet and underwent the same intense exercise training for four weeks. Blood levels of reactive oxygen metabolites (ROMs), which measure oxidative stress, and biological antioxidant potential (BAP), which measures blood levels of antioxidants, were determined pre- and post-supplementation. 

The results:

  • Control group had much higher ROMs post-exercise compared to pre-exercise
  • Probiotics group did not have a significant difference in ROMs levels pre- and post-exercise, which suggests that probiotics neutralized the exercise-induced ROMs
  • Probiotics group had higher BAP levels post-exercise compared to pre-exercise
  • Probiotics group had higher BAP levels post-exercise compared to control group

The data showed that intense exercise led to oxidative stress and probiotic supplementation increased antioxidant levels, which neutralized the ROS and oxidative stress. Notably, all athletes consumed antioxidants in their diet. Yet, because the gut microbiome regulates nutrient absorption, the higher BAP levels could be the result of greater antioxidant absorption by the probiotics. 

Oxidative stress resistance measures the ability of bacteria to survive oxidative conditions because of their ability to combat ROS. The study found that L. rhamnosus and L. paracasei had high-oxidative stress resistance; thus, demonstrating their antioxidative capacity. The high level of antioxidant enzymes in the bacterial strains can target ROS in the GI tract.

Lower Cholesterol

Athletes with high cholesterol (hypercholesteromia) or athletes trying to optimize cholesterol levels have a reason to use probiotics, specifically L. reuteri. The high number of hypercholesteromic people who are unable to optimize their LDL-C still remains a concern and exploration of other cholesterol-lowing therapies are needed. 

A randomized controlled trial found the cholesterol-lowering effects of L. reuteri. The 127 hypercholesteromic participants were randomly assigned to take the probiotic L. reuteri or placebo twice per day (at breakfast and dinner) for nine weeks. The L. reuteri capsules contained 2.9 x 10*9 CFU at baseline and 2.0 x 10*9 CFU at the end of the study. Blood samples were taken at six different visits to analyze serum levels of LDL-C, total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-C) and non-HDL-cholesterol (non-HDL-C).

The results:

  • Compared to placebo, L. reuteri capsules lowered:
    • LDL-C by 11.64%
    • TC by 9.14%
    • Non-HDL-C by 11.30%
    • Ratio of LDL-C/HDL-C by 13.39%

Finally, a recent meta-analysis by Guo et al. used data from 13 lipid-lowering probiotic trials (including L. acidophilus, L. plantarum, B. longum and B. lactis) and found that people with high, borderline high and normal cholesterol levels who received probiotics, compared to controls, had beneficial effects on total cholesterol and LDL cholesterol. The average net change was:

  • TC: -6.40 mg/dL
  • LDL-C: -4.90 mg/dL

How do Lactobacilli reduce cholesterol? Bile – which is made from cholesterol – helps digest fat. These gut microbiota can breakdown bile, which disrupts bile reabsorption and increases bile excretion. The lower amount of bile available for the body means more cholesterol is needed in the liver to make it. 

Niemann-Pick C1-like 1 (NPC1L1) is considered the major protein for intestinal cholesterol absorption. NPC1L1 is highly expressed at the surface of the small intestine. Even though it hasn’t been confirmed in humans, NPC1L1 deficiency in mice has shown a considerable reduction in dietary cholesterol absorption.  

Huang et al. found that the L. plantarum blocked cholesterol absorption by decreasing NPC1L1 after rats with high cholesterol were fed L. plantarum for four weeks at a dose of 10*9 CFU/day. Even though the study was conducted in rats, the results suggest the potential of L. plantarum for lowering cholesterol and the possible mechanism of how probiotics reduce cholesterol. The ability to decrease NPC1L1 expression was also found in L. rhamnosus. These results suggest that some strains of Lactobacillus may control cholesterol levels through NPC1L1. 

The Effect on Energy Regulation: Probiotics Produce Short-Chain Fatty Acids

Some nutrient digestion occurs in the stomach, but most nutrient digestion and absorption occurs in the small intestine. Absorption of all fats, ~85% of carbohydrates and 66-95% of proteins occurs before the large intestine. 

Non-digestible carbohydrates and protein in the colon account for 10-30% of total caloric intake. These indigestible nutrients wouldn’t be further absorbed and instead would be excreted if it weren’t for gut microbiota. Gut microbiota can produce many metabolites that regulate our health – specifically short-chain fatty acids (SCFAs), which have a positive impact.

Short-Chain Fatty Acids (SCFAs) 

Anaerobic intestinal microbiota can produce SCFAs by fermenting non-digestible carbohydrate (e.g., soluble dietary fiber) and proteins (e.g., branched-chain amino acids). Many gut microbes can ferment unabsorbed carbohydrate because they have the enzymes required. SCFAs can:

  • Shape the gut environment
  • Impact the physiology of the colon
  • Serve as energy sources for human cells (e.g., intestinal) and gut microbiota
  • Interact with host-signaling mechanisms

SCFAs increase the acidity of the gut, which increases the absorption of certain nutrients (e.g., magnesium and calcium) and stops pathogenic microorganisms from invading. 

The type and amount of SCFAs produced depends on our age, diet (e.g., availability of non-digestible carbohydrates), composition of gut microbiota, gut transit time and pH of the colon. The bacteria that produce SCFAs include:

  • Bacteriodes
  • Bifidobacterium
  • Lactobacillus
  • Faecalibacterium
  • Ruminococcus
  • And others 

In the gut, 90-95% of the SCFAs are: acetate, propionate and butyrate.

Acetate gives Bifidobacteria the ability to stop the microorganisms that cause disease in the gut. SCFAs provide energy for colon cells and nearby tissues. Acetate is the main SCFA in the blood and serves as an important energy source for peripheral tissues. Butyrate provides energy for intestinal cells and increases mucin production. The increase in mucin could possibly lower the amount of bad bacteria that attach to our gut and strengthen the gut barrier. These adaptations suggest SCFAs are critical in maintaining the function of our gut barrier. 

Following absorption of SCFAs, we use SCFAs in different biosynthetic routes. Our gut cells use butyrate, and the remaining SCFAs go to the liver for further metabolism. In the liver, SCFAs integrate into different carbohydrate and lipid metabolic pathways: 

  • Propionate is either used in gluconeogenesis (i.e., generation of glucose from non-carbohydrate sources) or regulates cholesterol synthesis
  • Acetate and butyrate is used in lipid and cholesterol synthesis

SCFAs have been associated with improving glucose tolerance by increasing the secretion of incretin hormone glucagon-like peptide (GLP)-1 and may increase the expression of vitamin D receptors on cells. 

Probiotics: Linking Optimal Digestion and Absorption of Nutrients

Dysbiosis from a dysregulated or dysfunctional microbiome may lead to consequences involving inefficient nutrient use. Gut bacteria can improve our nutrient absorption, especially of vitamins and minerals. By-products from probiotic metabolism (e.g., SCFAs) demonstrate the indirect, positive health effect that probiotics can also lend.

Certain probiotics positively impact our nutrition because they have some metabolic tools we don’t have: the genes to make vitamins, the ability to shape the gut environment to increase absorption of certain nutrients and the enzymes to breakdown non-digestible macronutrients to metabolites that positively influence our health. Ultimately, probiotics are important players that bring together nutrition, gut health and human physiology.

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.

Full text and references

Beet Boosting Bugs

Are you drinking your beets?

You have likely heard about the performance-enhancing superfood, beetroot. Or maybe you have already incorporated it into your training. Either way, it’s hard to ignore the growing attention paid to beetroot. But how does this dark red root improve your 10k time and are there ways to get more out of your glass of beetroot juice?

The mechanism behind beetroot’s boost lies in nitrates. Nitrates are a chemical compound found in beetroot as well as dark, leafy vegetables. When we ingest nitrates they get converted into nitric oxide (NO). Our bodies use NO in a variety of ways, but NO is the link between beetroot and improved performance.

Jason Houston at BeetBoost explains it like this: 

NO relaxes the muscles by widening blood vessels when it spreads through underlying muscle cells in the arterial walls. This affects how efficiently cells use oxygen — efficient oxygen use is a very good thing — and this is one of the reasons why beetroot juice can be used to support sport performance. 

For an excellent, and more detailed look at this process read InsideTracker’s article .

In order for this process to occur, it turns out that our bodies need a little help from the bugs inside us to get the performance boosting benefits from nitrate. The bacteria in our gastrointestinal tract play a huge role in NO production – from our oral cavity to our colon. The name of this system is a mouthful (pun intended): the entero-salivary nitrate-nitrite-NO pathway. The nitrate in foods like beetroot get broken down by bacteria in the mouth, stomach and small intestine and eventually converted to NO.

We know that bacteria play a pivotal role in NO production throughout the entire gastrointestinal tract based off several studies. In one such study, researchers eradicated the bacteria of the mouth using mouthwash. This effectively destroyed the bacteria in the mouth that help convert the nitrate to NO. Subsequently, they found that NO levels were reduced and the benefits of the nitrate were lost. The take home message here is go easy on the Listerine!

Also, studies have shown that germ-free mice (no bacteria in the gut) do not effectively produce NO. Furthermore, rats supplemented with lactobacilli probiotics in conjunction with a nitrate load resulted in a 3-8 fold NO increase in the small intestine. It is studies like these that have lead researchers to believe that our microbiome plays a key role in the production of NO from dietary nitrate. In fact, it has been theorized that some of the beneficial effects of probiotics might be mediated through NO. 

The studies are fascinating, but inevitably lead to more questions: What is the optimal beetroot/nitrate dose? Would particular probiotic strains plus beetroot, augment the production of NO more than the beetroot alone? Are microbiomes of various dietary patterns more conducive to NO production?

What we do know is this: beetroot improves select performance parameters via NO, and our microbiome plays an integral part in the production of NO. More studies will lead to even better insights, but it is obvious that if you want more out of your beets and sports nutrition, it pays to take care of your gut.

Inflammation, Your Gut and Performance


We recently had a great conversation with our friends at Endurance Planet about gut health, probiotics, and the endurance athlete (check out the podcast). The question of how inflammation affects performance came up and I felt like revisiting the issue a bit more extensively in this post.

Inflammation is not necessarily the boogeyman that it is often believed to be. To understand how inflammation might affect athletic performance, let’s first define inflammation and its role in the body.

Inflammation is an extremely complex and dynamic process. It functions appropriately in our bodies as a means of warding off infections and responding to injured tissues. Think of inflammation as a cascade of events with the infection (injury, toxin, or stressor) resulting in the release of particular cells and chemicals that go after the infection or injured tissue to either destroy the offending stimulus or protect/repair the injured tissue. Inflammation is what leads to pus and to the straw-colored fluid in blisters. But most often the reaction goes on unseen inside our bodies.  

It is important to understand that infection is not the same as inflammation. An inflammatory response occurs as a result of an infection, but that is not the only time inflammation occurs in the body. Exercise is a well established cause of inflammation too. Exercise can lead to tissue (ie, muscle) injury, which sets off a cascade of inflammation. However, this is a short-term effect. Exercise has actually been found to have a long-term anti-inflammatory effect

So when is inflammation bad? This is a tough question without a good answer, but I think it would be generally accepted that inflammation, when chronic, is doing more harm than good. When does inflammation become chronic? Well, neither that blister nor that cold will last forever, so for the majority of us it’s not nasty bugs or autoimmune conditions that are driving chronic inflammation. It is our diet and stress!

The link between our diets and chronic, systemic inflammation is thought to be mediated through our guts. A less diverse microbiota, associated with a typical Western diet, has been linked to increased intestinal permeability. This process allows substances that should not cross into the bloodstream do so, triggering an inflammatory response. This process has been linked with increased insulin resistance and in turn obesity and type II diabetes. Current research is also pointing toward chronic inflammation as a culprit in the development of cardiovascular disease and even depression.

How does inflammation affect performance

As I mentioned earlier, exercise actually causes inflammation, but it dissipates within hours to days with adequate recovery. The problem arises, when you don’t allow for adequate recovery or add on other stressors (ie, poor diet, poor sleep, alcohol, etc) that augment the inflammation leading to, you guessed it – chronic inflammation. At this point, you are treading in dangerous territory and run the risk of overreaching and overtraining.  IF we are to assume that these syndromes represent a state of chronic inflammation – or are in fact synonymous, then we can most definitely say that they affect performance!

What to do about it

Proper Nutrition: Despite some good guiding principles with nutrition and hydration, what you consume is a very personal choice, and it takes a lot of self-experimentation to figure out what works. But the bottom line is that you should take as much care with what you put in your body as you do with picking out your gear. Check out Endurance Planet for several great podcasts on nutrition for athletes as well as the website for a leading exercise physiologist Asker Jeukendrup

Proper sleep: Get it! Read more about gut health and sleep here

Maintain a healthy gut: Personally, this doesn’t have anything to do with adhering to a specific diet or relying heavily on a particular food group, but rather focusing on the least refined, most natural foods I can find. I also eat a wide array of fermented foods/drinks like miso, kombucha, and sauerkraut. The goal is to increase microbial diversity in our gut. Increased microbial diversity is associated with less inflammation.

Proper sleep and reducing stress also have beneficial effects on gut health.

Avoid unnecessary antibiotics. Don't be quick to accept an antibiotic prescription. Ask your doctor if it is really needed and if "waiting it out" might be a better option (as is the case for a cold and most sinus issues). 

Avoid excessive alcohol

Don't take NSAIDs for pain

Get a coach: A coach can keep track of your training intensity and see patterns in your performance that will prevent you from overreaching and aid in proper recovery. A good coach is worth every penny!