There has been a lot of robust literature examining the effects of gut bacteria on our general health and wellbeing, mood, and even athletic performance. Our gut bacteria produce metabolites from the food that we eat and—in turn—go on to impact many of the hormonal responses that happen within our bodies. The variation of the bacteria that comprise our gut can modulate what’s happening to our central nervous system, our immune system, how we respond and adapt to training, and of course, our mood.
Two major groups, Bacteroides and Firmicutes, make up most of the human gut microbiome and are the two that are most directly involved with body composition and inflammation. Most studies have shown that the more Bacteroidetes you have (compared to your Firmicutes), the leaner you will be and the less issues you will have with inflammation. We can alter the ratios to some extent by the foods we eat and the exercise we do, but by the time we reach the age of three our gut microbiome is largely determined (due to environment, type of birth, breastfeeding, and genetics). We also know that the more diverse the gut microbiome is, then the leaner individuals are and the more stable their autonomic nervous system is (e.g. heart rate variability, digestion).
Part of the benefit of moderate exercise is increasing that diversity of bacteria. When you’re exercising on a regular basis and reducing the oxygen and increasing the heat that goes to the gut, you are creating an environment that allows some bacteria to grow and stunts the growth of others.
But on the other end of the spectrum, it is worth being aware of the impact that extreme exercise, such as long-course triathlon, can have on the gut microbiome. Training and racing for these types of events—if you’re not careful about nutrition and recovery—can really affect the diversity and integrity of the gut microbiome. It is known that extreme exercise increases inflammation, which can directly influence the bacteria that, in turn, keep creating this inflammation, and a vicious circle ensues. Equally, the use of large, but necessary, amounts of simple carbohydrates (gels, chews, energy drinks) during training can stimulate the growth of inflammatory bacteria. When you’re not exercising, you then have an overgrowth of that bacteria that will stimulate you to crave more simple sugars.
When we are looking at how we use exercise and nutrition to improve gut health, we want to enhance the bacteria that improve our fitness adaptations. Remember that the foods you eat will affect your gut microbiome and this will go on to affect your mood, body composition, sleep, immunity, and cardiovascular health—in short, every system in your body.