The human microbiome is a modulator of immune function, inflammation, energy harvest, metabolism and oxidative stress (6) yet it is rarely discussed in athlete nutrition programs. If you are feeling a bit lost, you may have missed Part 1 of the Athlete Microbiome series. In Part 1 we covered what the microbiome is, what factors can influence your microbiota health and what a not so healthy microbiome looks like (dysbiosis). Part 2 will be taking you through the specifics of what we know about the athlete microbiome, and how it can affect digestive function and inflammation, energy production and mental health in athletes.
Research on the microbiome has been growing exponentially in the last 10-15 years, but when it comes to athlete populations- there is still a lot to learn. One of the first studies to focus on the athlete microbiome utilized elite rugby players versus age matched sedentary controls as test subjects (1). They discovered a much higher microbial diversity in the athlete group vs. sedentary control group (1). In Part 1 of this series, we learned that bacterial diversity is crucial to overall microbiota health. So- this study helped pave the way for the hypothesis that exercise and training is beneficial for our microbiome. In the same study, they found a greater prevalence of specific strains of bacteria in athletes such as Akkermansia and prevotella species (1). The latter of which is associated with increased branched chain amino acid (BCAA) metabolic pathways (7) . This is a plausible adaptation, as athletes may need a greater abundance of these bacteria to further support muscle metabolism and recovery pathways (7).
Overtraining is a well known threat to athlete health and recovery. Athletes are constantly putting their body under intense physical and mental stress. Overtraining can lead to an inflammatory state and subsequently decreased immune function, mental health and induce gastrointestinal distress (10). To determine the effects of overtraining on the microbiome, researchers utilized an animal model where they put mice through a rigorous training regime and analyzed changes in their microbiome (10). Resultant data showed that overtrained mice had a decreased microbiota diversity (10). While further studies with human subjects are necessary to further evaluate the effect of overtraining on microbiota, it is an interesting concept that could potentially be utilized in the future to help offset decreases in immune function , energy levels and recovery for athletes during intense periods of training.
Overall, when it comes to the health of an athlete microbiome, it is multifactorial. We know we are studying a population that is likely more health conscious than the average individual, and thus more aware of dietary choices. Dietary choices can account for up to 57% of microbiota changes (2). The athlete's diet is typically high in protein, carbohydrates and low in complex fibers - a huge factor in the health of an individual's microbiome (2). (More on dietary changes influence on the microbiome to come in Part 3)
Exercise induced gastrointestinal (G.I) distress is common in athletes, especially as the intensity of exercise training increases (2). During intense exercise, we see an increased production and secretion of stress hormones and pro-inflammatory substances such as lipopolysaccharides (LPS)(2). High circulating levels of these inflammatory substances can increase intestinal permeability and lead to syndrome more commonly known as ‘leaky gut’ (2). Symptoms of G.I distress are more common in high level endurance athletes, who have been shown to have high circulating blood levels of LPS (2). Approximately 20-60% of athletes suffer from gastrointestinal symptoms such as diarrhea, bloating, nausea, vomiting and cramping (2). Leaky gut can have some serious downstream consequences when it comes to athlete health and performance. Improving microbiota health through increased diversity and abundance of short chain fatty acids (SCFA) to help support the integrity of the intestinal lining, decrease inflammation and prevent leaky gut is a key factor in improving the health and performance of athletes (2). Stay tuned, for Part 3 of the Athlete Microbiome series where we will discuss the role of probiotics in improving athlete microbiota diversity and decrease gastrointestinal inflammation.
Mental health is directly correlated with the health of our microbiome. This relationship is known as the ‘Gut-Brain Axis’ (5). The brain and gut communicate via a bi-directional highway of neurotransmitters, hormones and the vagus nerve (5). For example, almost 95% of the body's serotonin production occurs in the gut (5).
Athletes are at greater risk of mental health disorders (anxiety, depression) than the general population (8). Athletes are constantly under pressure to perform and excel by coaches, teammates, parents, the media and most importantly - themselves. In addition, athletes are at greater risk of traumatic brain injuries (TBI) which may further exacerbate mental health conditions (8). Only recently have we seen athletes begin to open up about their struggle with mental health and all brave enough to express the tremendous pressure that athletes experience on a daily basis. Most recently, Naomi Osaka expressed that she had been suffering from anxiety and depression worsened under social situations and competition. We cannot address the mental health of athletes without also understanding the huge role which the health of our microbiome can play. Future considerations for research on this topic should start to explore the gut-brain axis in athlete populations.
The health of our microbiome can directly affect metabolic parameters and body composition. Studies done in mice have shown that transferring an obese type microbiome to a lean, germ-free mouse results in rapid weight gain and increased fat mass (5). The health of our microbiome can directly affect metabolic parameters associated with blood sugar regulation such as insulin levels and triglyceride levels (5) which can significantly impact the health status of an individual.
So- how does the bacteria in our gut lead to changes in body composition ?
First, let's take a step back and define some terms. ‘Energy harvest’ is a fancy way of describing the amount of calories that our body will utilize versus (ahem) ...excrete. The microbiome does this via metabolizing indigestible complex carbohydrates into short chain fatty acids (SCFA)(5). SCFA are subsequently utilized as an energy source and lead to an increased energy harvest from food we consume (5). So - if we have a healthy microbiome that is producing SCFA such as butyrate, propionate, and acetate , we see an increased uptake of calories (pretty cool right?!). In addition, the health of our microbiome can also affect other parameters related to body composition such as appetite regulation, cravings and satiety (5). Our hunger hormones, leptin and ghrelin, can be regulated by the health of our microbiota (5). The current focus on the metabolic effects of the microbiome has been focused on obese populations, more research on lean type individuals such as athletes needs to be done to determine how the microbiome can affect the metabolism of active individuals.
The microbiome is a modulator of athlete immune function, digestive health, body composition and energy metabolism and inflammation. The research supporting the impact of the athlete microbiome on various parameters is rapidly growing and slowly beginning to translate into applicable supplemental and nutritional protocols. Recent studies have even been able to connect certain microbes with improved energy conversion and thus enhanced performance (9). Stay tuned for Part 3 of the athlete microbiome series, where we will dive into the most common supplements and dietary strategies to support a healthy, diverse and thriving microbiome.