Written by Callen Goldsmith (science graduate and avid runner).

Remember back to when I was talking about protein? I briefly touched on gut microbiota, but since there’s at least as many of them as our own body cells if not more, they probably deserve their own article or two. The gut microbiome sounds kinda boring, like something a teacher would describe in lots of big Latin words. Most people probably don’t even know what it is or just recall some vague concept like ‘tummy flora’ when it’s mentioned.

The microbiome that each of us carries around in our bodies heavily influences multiple aspects of our lives. You probably wouldn’t even suspect half of them. Gut bacteria have been implicated in many neurological disorders such as Autism Spectrum Disorder, Schizophrenia, and anxiety disorder. There is also evidence linking the microbiome to people’s likelihood to gain weight and become obese. That’s right, you can blame your gut for your… gut. But recently, some investigations into the gut microbiome suggest it might manipulate aerobic capacity and that the athlete lifestyle could alter our tummy flora for better or worse.

Today we’ll focus on how our training and diet might be having broader consequences for our competition performance and overall health.

Escaping the bog monster

It is well known that increasing protein intake is beneficial for athletes of all types. Athletes have way higher rates of muscle damage because of their high exercise volumes, so they need the extra protein to repair them. Calculating these requirements gives the recommended 1.2-2.0g/kg/day protein intake for middle/long-distance runners. 

The conventional wisdom also calls for eating lots of carbs, as they are the most efficient and primary fuel for running. High energy carbs are often focused on before and after training to avoid “gastrointestinal complications” while running. Put simply, this means avoiding a surprise encounter with a turtle head mid-run. These high energy carbs usually lack fibre since it’s harder to digest.

A few studies have shown that distance runners who aren’t eating enough fibre but consume extra protein have fewer tummy microbes than they should. This decline in diversity and number of microbes is especially prevalent in athletes who engage in super specific long-term diets that might neglect certain nutrients such as fibre.

Worryingly, low numbers of microbiota are also associated with obesity and a greater likelihood of gaining fat. Increased body fat in runners is not conducive to faster times, so it’s probably worth avoiding. As far as I know, there aren’t reports showing that fibre deprived athletes get fat, but the links are still concerning. In any case, a depleted microbiome doesn’t sound like a good thing. 

Luckily, there have been studies on athletes who achieve all their nutritional requirements. The results from these studies showed that by eating more protein, their bacterial diversity actually increased! So maybe a poo stop on the run isn’t so bad? Plus, it would be easy enough to have sufficient fibre and manage to avoid it before training sessions or races to escape the bog monster.

Friendly Fatty Acids

Short-chain fatty acids (SCFA’s) are something that the gut microbiota produce when they digest certain foods. The SCFA’s are integral for maintaining a healthy body. Athletes who consume lots of protein but lower carbs (and fibre) in their diet have less production of SCFA’s. This has been linked to adverse health outcomes. 

Mice who had less SCFA production had a marked decrease in their endurance capacity and overall muscle function. What’s more, those with lower gut biodiversity and less SCFA’s showed insulin resistance and increased blood lipids. These symptoms are like that of obese/overweight people who are pre-diabetic. 

Unsurprisingly, athletes who focused on meeting their energy requirements but incorporated sufficient fibre and protein (and everything) into their diet had a richer, more abundant SCFA profile. A strong SCFA profile is indicative of good health and a lean physique

This is what you want because staying healthy is super essential for achieving running-related goals. Plus, not carrying excess or unnecessary weight always helps to run faster and fatigue slower.

Your gut loves soy 

Soy protein has also been linked with reduced blood lipids, along with other cardiometabolic health parameters. Given heart disease is the number one killer in the world, this is an important finding.

One study found that compared with whey, which we know is the best at growing muscles, soy protein actually increased the biodiversity of the gut microbiota. Although this study was performed with guinea pigs, the results are generally applicable to humans too. Unfortunately, exercise was not tested, meaning we are unaware whether this results in an additional performance benefit outside the well studied benefits of protein intake. 

Disappointingly, soy protein has been given a bad name. There are wild claims that it causes decreased testosterone and feminises males. To those people, I say: oh stop it you ;). Honestly, the studies that found any link between soy and the creation of ladyboys mostly were case studies of males who were seshing absurdly large quantities of it. Massive volumes of any nutrient no matter how good it might be is usually not good. I’m sure I don’t have to explain that sitting at home and drinking endless litres of soy milk isn’t going to be conducive to good health. 

What have we learnt?

Our gut microbiome is essential to our overall health. Ensuring it remains intact and well-functioning should be a high priority on anyone’s radar, athlete or not. The athlete diet can have negative impacts on our tummy flora when particular nutrients are neglected. Ultimately, it comes down to eating a balanced diet that meets your energy requirements that ensures variety with no nutrients left behind. Stay tuned to learn more about how the gut microbiome can improve your athletic prowess soon.

Recommended further reading

  1. Barton, W., Penney, N. C., Cronin, O., Garcia-Perez, I., Molloy, M. G., Holmes, E., Shanahan, F., Cotter, P. D., & O’Sullivan, O. (2018). The microbiome of professional athletes differs from that of more sedentary subjects in composition and particularly at the functional metabolic level. Gut, 67(4), 625–633. https://doi.org/10.1136/gutjnl-2016-313627
  2. Butteiger, D. N., Hibberd, A. A., McGraw, N. J., Napawan, N., Hall-Porter, J. M., & Krul, E. S. (2016). Soy Protein Compared with Milk Protein in a Western Diet Increases Gut Microbial Diversity and Reduces Serum Lipids in Golden Syrian Hamsters. The Journal of nutrition, 146(4), 697–705. https://doi.org/10.3945/jn.115.224196
  3. Clarke, S., Murphy, E., O’Sullivan, O., Lucey, A., Humphreys, M., & Hogan, A. et al. (2014). Exercise and associated dietary extremes impact on gut microbial diversity. Gut, 63(12), 1913-1920. doi: 10.1136/gutjnl-2013-306541
  4. Jaago, M., Timmusk, U. S., Timmusk, T., & Palm, K. (2021). Drastic Effects on the Microbiome of a Young Rower Engaged in High-Endurance Exercise After a Month Usage of a Dietary Fiber Supplement. Frontiers in nutrition, 8, 654008. https://doi.org/10.3389/fnut.2021.654008
  5. Jang, L. G., Choi, G., Kim, S. W., Kim, B. Y., Lee, S., & Park, H. (2019). The combination of sport and sport-specific diet is associated with characteristics of gut microbiota: an observational study. Journal of the International Society of Sports Nutrition, 16(1), 21. https://doi.org/10.1186/s12970-019-0290-y
  6. Le Chatelier, E., Nielsen, T., Qin, J., Prifti, E., Hildebrand, F., & Falony, G. et al. (2013). Richness of human gut microbiome correlates with metabolic markers. Nature, 500(7464), 541-546. doi: 10.1038/nature12506
  7. Moreno-Pérez, D., Bressa, C., Bailén, M., Hamed-Bousdar, S., Naclerio, F., Carmona, M., Pérez, M., González-Soltero, R., Montalvo-Lominchar, M. G., Carabaña, C., & Larrosa, M. (2018). Effect of a Protein Supplement on the Gut Microbiota of Endurance Athletes: A Randomized, Controlled, Double-Blind Pilot Study. Nutrients, 10(3), 337. https://doi.org/10.3390/nu10030337
  8. Reed, K., Camargo, J., Hamilton-Reeves, J., Kurzer, M., & Messina, M. (2021). Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies. Reproductive Toxicology, 100, 60-67. doi: 10.1016/j.reprotox.2020.12.019