What illness, immune resilience, and missed days mean for athlete availability
Here I am again, continuing my series on athletes, performance biology, and how it ties to the gut. I would never have imagined I would not only write about this, but write about it in a series. C’est la vie. You never know where it will take you.
So let’s talk athletes. Extraordinary talent. Extraordinary performance. They can be fast, strong, skilled, and perfectly conditioned. But if an athlete can’t practice or play, none of those qualities are useful to the team that day.
That may be painfully obvious to everyone who works in professional sports. It wasn’t something I had ever really thought about. Then again, neither was gut training until last week.
Four articles into Performance Biology, I’m beginning to see professional sports very differently. Teams monitor sleep, training load, nutrition, hydration, recovery, movement, and an astonishing amount of information about how an athlete’s body is functioning. But ultimately, much of that work has a remarkably simple objective: Keep the athlete healthy, recovered, and available to play. And, as seems to happen every time I research one of these topics, that brought me back to the gut. Again.
Not Every Missed Day Is an Injury
When most people think about athlete availability, they probably think about injuries. The torn ACL. The hamstring. A concussion. The shoulder. But athletes also miss or modify training because they get sick. Respiratory infections, stomach bugs, viruses, the flu. Or they may technically be able to play while feeling considerably less than capable of performing at an elite level.
Did you know that the International Olympic Committee has devoted an entire scientific paper to respiratory illness in athletes, including its effect on performance and returning to play? It caught my attention because suddenly illness isn’t just a health issue. For a professional team, it’s an availability issue.
A player doesn’t have to be hospitalized or officially ruled out for illness to matter. Missed practices, poor sleep, reduced fueling, or diminished performance have consequences of their own.
Athletes Have Immune Systems Too
I know. Another revelation from the woman who only recently discovered gut training. But of course they do. They’re human, are they not? For years, we heard a fairly simple explanation: hard exercise can weaken the immune system and make athletes more likely to get sick. Today, scientists know it’s more complicated than that. Training is important, but so is sleep, nutrition, stress, recovery, travel, and exposure to illness. And guess what shows up again? You got it. The gut.
A huge part of the body’s immune system is connected to the gut. And the trillions of microorganisms living there aren’t just hanging around waiting for a protein bar or lunch. They produce substances that interact with the body and with immune cells.
That does not mean the microbiome controls the immune system. It doesn’t. But the gut and immune system communicate with each other all the time, and I am all in favor of eavesdropping.
Here’s Where I Start Flailing My Arms
Researchers have been studying probiotics in athletes for years. The results aren’t a slam dunk, but they’re interesting. One large review looked at several studies involving athletes taking probiotics. They didn’t get sick significantly less often or recover significantly faster.But researchers found something else. When athletes taking probiotics did get sick, their respiratory symptoms tended to be less severe.
There are still plenty of unanswered questions. Different probiotics contain different bacteria, and different athletes put very different demands on their bodies. Fair.
Then I moved from probiotics to thinking about postbiotics and athletes. So I dug in. Postbiotics are different than pre or probiotics. They contain microorganisms that are no longer alive, or parts of them, but can still have beneficial effects in the body. And that’s where I really started flailing my arms.
A 2024 review pulled together 11 studies involving nearly 500 people and found early signs that certain postbiotics may affect fatigue, recovery, immune health, and even some measures of physical performance.
Let me emphasize early signs. We are nowhere near being able to say postbiotics make someone a better athlete. Tempting, but no. However, one study really got my attention. Male athletes doing repeated, high-intensity training were given either a placebo or a supplement made with heat-killed bacteria. Yes. Dead bacteria.
The athletes who got the heat-killed bacteria reported fewer days with respiratory symptoms and fewer days of fatigue. It didn’t improve everything researchers measured, and one study certainly doesn’t prove that postbiotics keep athletes healthy. But apparently bacteria don’t necessarily have to be alive to do something useful.
I find that utterly fascinating. And if this is interesting to a non-sports fan, how could trainers, nutritionists, and professional performance departments not find it fascinating? And potentially really, really helpful?
Are Performance Departments Asking the Wrong Question?
I started out wondering whether a fermented product containing prebiotics, live probiotics, and compounds produced during fermentation (postbiotics) could help keep athletes from getting sick. That’s an appealing question for someone who owns a company that makes a fermented gut-health product. Ahem, Original Biome.
But it’s probably too simplistic. Maybe the better question is whether gut health belongs somewhere in the larger strategy teams use to keep athletes healthy and available. Teams already think about nutrition, hydration, sleep, recovery, training load, and travel. Each is one piece of a much larger puzzle. Why would the gut be any different?
Not because supporting the microbiome guarantees fewer sick days. I clearly cannot say that. But the gut is connected to all of those pieces, as well as digestion, the immune system, stress, and other things teams may already be trying to manage.
Maybe it belongs in that group.
Which Brings Me Back to Availability
I started this series wondering whether professional sports had become better at measuring recovery than influencing it. Four volumes later, here is what I know for sure: The athlete’s biological systems are interconnected.
A disrupted night of sleep isn’t only about sleep. Travel isn’t simply transportation. Food isn’t useful simply because someone ate it. And illness doesn’t suddenly become relevant only when it’s severe enough to keep an athlete out of the game. So maybe the question isn’t whether the microbiome can make an athlete faster, stronger, or less likely to get sick. Those claims get ahead of the science, at least for now.
The question I find much more interesting is this: If athlete availability is one of the most valuable outcomes in professional sports, are teams measuring and supporting all of the biological systems that may contribute to it—including the gut?
I don’t know. But I’ve stopped wanting to simply read or write about it. I want to know what would happen if someone actually tested it and measured it. Can we do that?
References
Schwellnus M, Adami PE, Bougault V, et al. International Olympic Committee consensus statement on acute respiratory illness in athletes part 1: acute respiratory infections. British Journal of Sports Medicine. 2022;56(19):1066–1088. doi:10.1136/bjsports-2022-105759.
Łagowska K, Bajerska J. Probiotic Supplementation and Respiratory Infection and Immune Function in Athletes: Systematic Review and Meta-Analysis of Randomized Controlled Trials. Journal of Athletic Training. 2021;56(11):1213–1223. doi:10.4085/592-20.
Di Dio M, Calella P, Cerullo G, et al. Effects of Probiotics Supplementation on Risk and Severity of Infections in Athletes: A Systematic Review. International Journal of Environmental Research and Public Health. 2022;19(18):11534. doi:10.3390/ijerph191811534.
Mohr AE, et al. It’s Dead! Can Postbiotics Really Help Performance and Recovery? A Systematic Review. Nutrients. 2024;16(5):720.
Komano Y, Shimada K, Naito H, et al. Efficacy of heat-killed Lactococcus lactis JCM 5805 on immunity and fatigue during consecutive high intensity exercise in male athletes: a randomized, placebo-controlled, double-blinded trial. Journal of the International Society of Sports Nutrition. 2018;15:39. doi:10.1186/s12970-018-0244-9.
