The Gut Microbiome: Setting The Mood With Food

By Austin Mark, RD

Have you ever wondered what it would be like to rule the world? In many ways, you already are without even realizing it. The human body hosts more than 100 trillion microorganisms in the GI tract commonly referred to as the gut microbiome. Through the way we live, we can greatly impact the diversity and functionality of these microorganisms (Clark & Mach, 2016). These microorganisms play a role in nutrient uptake, vitamin synthesis, energy harvest, inflammatory modulation, immune response, gut motility, appetite, serotonin production, and much more (Mohr et al., 2020; Clark & Mach, 2016). The success of these functions relies heavily on the diversity of the gut microbiome and are influenced by age, genetics, drug use such as antibiotics, stress, smoking, physical activity, and most importantly diet which accounts for up to 57% of gut microbiota changes (Mohr et al., 2020; Clark & Mach, 2016). The power to influence these factors through lifestyle choices and make these organisms work for you instead of against you is a great advantage to optimize performance, recovery, mood, and overall health.

The athlete today is faced with an endless list of stressors such as work, school, busy schedule, practice, lift, finding time to eat, managing family/relationship time, and a global pandemic to top it off. Stress can be shown through fatigue, performance decline, insomnia, change in appetite, weight loss, mood disturbances (irritability), anxiousness, loss of motivation, poor concentration, depression, and inflammation (Clark & Mach, 2016). It can be hard to distinguish between physical and psychological stress, but it is known that 20-60% of athletes suffer from the stress caused by excessive exercise and inadequate recovery (Clark & Mach, 2016).

Establishing a diverse and functional gut microbiome is essential to combat taxing stress accumulated from an athletes’ training regimen. A poor-quality diet with predominant and frequent intake of saturated fats, refined grains, sugar, salt, alcohol, meat/processed meat, corn-derived fructose (i.e., high-fructose syrup) can create an imbalance of gut microbiota linked with disease, otherwise known as dysbiosis. This can cause inflammation, intestinal permeability, erosion of the mucus layer important for protecting our gut from letting outside invaders into the body, and pathogenic infection.

This type of diet also may not support a high production of short-chain fatty acids (SCFAs) (Mills et al., 2019). SCFAs are made when bacteria in our GI tract ferment dietary fibers. This is a good thing, as SCFAs get absorbed by the body to help produce energy, maintain intestinal barrier integrity to protect from inflammation, positively affect brain function, directly affect immune cells to maintain homeostasis, and more (Dalile et al., 2019). SCFAs may also play a critical role in serotonin (feel-good hormone) production. 95% of serotonin is produced in our intestines, and SCFAs help produce the enzymes needed to synthesize serotonin (Dalile et al., 2019). Low serotonin in the brain causes sleep drowsiness, fatigue, mood disorders, and depression leading to decreased performance and a likely vicious cycle of exercise-induced stress with an ill-equipped gut microbiome to fight the stress. For example, the dysbiosis mentioned earlier and exercise-induced intestinal permeability can allow lipopolysaccharides (LPS) to leak into the body. LPS is found on the outer membrane of bacteria and may cause low-grade chronic inflammation (Mohr et al., 2020).

Flipping the script

Athletes account for macronutrients, micronutrients, hydration, nutrient timing, and dietary supplements, but rarely are there ever recommendations for optimizing the gut microbiome as the focus is on other factors around performance and recovery (Mohr et al., 2020). In order to optimize the gut microbiome, athletes may benefit from more careful consideration of the nutrients which support the growth and health of beneficial microorganisms. The focus here is dietary fiber and prebiotics from plant foods. Eating foods rich in fibers that are fermentable help feed starving microorganisms. Examples are fruits, vegetables, whole grains like oats, barley, and wheat, legumes like beans and peas, and potatoes. While it may seem simple, it can be difficult to eat enough fiber every day if not being intentional. Recommendations are 25g/day for women and 38g/day for men, though the actual average intake is closer to 15g/day (Mills et al., 2019). Keep in mind, individuals who eat more plants on a daily basis have greater diversity of gut microbiota, which supports immune homeostasis, healthy intestine mucus layers, high SCFA levels, influences serotonin levels, mitigates stress and inflammation, creates sustainable energy, and much more. Gut microbiome composition changes have been reported within 24 hours of dietary changes (Mohr et al., 2020). This means that changes today can affect you tomorrow!

Approach as a coach

Understanding your athletes can give you an advantage to see if an athlete is suffering from stress (Clark & Mach, 2016), and help them understand ways their food affects their body. If an athlete appears depressed, tired and fatigued with no immediate mental health concerns, referring them to a local sports dietitian can help determine if their nutrition behaviors might contribute to poor gut health, and their mood and stress. Identifying

This article was written by a Collegiate and Professional Sports Dietitian Association Registered Dietitian (RD).  To learn more about sports nutrition and CPSDA, go to


Clark, A., & Mach, N. (2016). Exercise-induced stress behavior, gut-microbiota-brain axis and diet: a systematic review for athletes. Journal of the International Society of Sports Nutrition, 13(1).

Mohr, A. E., Jäger, R., Carpenter, K. C., Kerksick, C. M., Purpura, M., Townsend, J. R., … Antonio, J. (2020). The athletic gut microbiota. Journal of the International Society of Sports Nutrition, 17(1).

Dalile, B., Van Oudenhove, L., Vervliet, B., & Verbeke, K. (2019). The role of short-chain fatty acids in microbiota–gut–brain communication. Nature Reviews Gastroenterology & Hepatology, 16(8), 461–478.

Mills, S., Stanton, C., Lane, J., Smith, G., & Ross, R. (2019). Precision Nutrition and the Microbiome, Part I: Current State of the Science. Nutrients, 11(4), 923.

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