A few years ago, when Colgate University biologist Kenneth Belanger was extending his research scope to include microbiomes, he met with experts from multiple disciplines, including those from the university’s athletics department. “[We realized] one of the real concerns…in athletics [is] the effect of head impacts on the brain and on systems beyond the brain.”
Kenneth Belanger is a biologist at Colgate University
Adam Brockway, Colgate University
While scientists have previously shown that concussions in football players disrupt their gut microbiomes, researchers did not know whether non-concussive head impacts led to a similar effect.1 This question is particularly important since American football players experience between 100 and 1,000 head impacts across a season.2
To fill in the gap, Belanger joined forces with Colgate University systems biologist Ahmet Ay, student athlete Zachary Pelland, and undergraduate student Aziz Zafar, now a graduate student at Columbia University.
Recently, the team of researchers found that non-concussive head impacts that did not cause any clinically detectable symptoms in six football players were correlated with changes in the gut microbiome.3 Their findings, published in PLoS One, offer early clues in identifying gut microbiome-associated biomarkers for assessing the severity of head trauma.
“[We need] more papers like this one,” said Sonia Villapol, a neuroscientist at Houston Methodist Research Institute, who studies the gut microbiome in neurotrauma and was not associated with the study. “They are very important because players and athletes in general need biomarkers for concussions or repetitive hits.”
For their study, Belanger and Ay recruited six American football players aged 21 to 22. They monitored the athletes’ on-field activities during both practice and games throughout a competition season via a sensor-based monitoring system embedded in their helmets, which measured the force of the impacts.
Ahmet Ay is a systems biologist at Colgate University.
Dylan Crouse, Colgate University
Each of the participants also submitted fecal samples over the course of the season and filled out questionnaires that helped assess their experiences and behaviors during the day before the sampling. At the end of the study duration, the researchers had collected 226 usable stool samples.
The researchers isolated DNA from these and sequenced it to obtain the gut microbiome composition. They observed significant changes to the microbial diversity two to three days after a player experienced a significant head impact.
Given the already-established association between head injuries and gut microbiomes, Belanger was not entirely surprised by their results. “But, it seems like there is this link between the two that doesn't require the head impact to be so significant that it's causing loss of consciousness or any of the other sort of symptoms that you imagine with a concussion,” said Belanger.
Ay agreed. He said, “It was interesting to me because these are very…small head impacts.”
Zachary Pelland is a football player and neuroscience student at Colgate University.
Adam Brockway, Colgate Athletics
A closer inspection revealed that bacteria belonging to the genus Ruminococcus increased in abundance, while those belonging to the order Coriobacteriales, the family Prevotellaceae, and the genus Prevotella decreased. Both Ay and Belanger noted that more work needs to be done to investigate whether these microbiome changes were protective and beneficial for recovery or were a result of neuroinflammation.
The researchers also observed a shift in the players’ gut microbiomes across the season. Mathematical modeling to account for variable factors such as diet, sleep, exercise intensity, and stress indicated that the microbiome changes were likely associated with head impacts.
“It's nice that they have this data [from] measuring the impacts in the helmets,” said Villapol. However, she noted that their insight into microbiome alterations is limited to the bacteria’s phyla. According to her, applying metagenomic analyses could fill this gap and offer deeper, species-level information. She also noted that supplementing such analyses with metabolomics can offer crucial clues into the roles that the disrupted bacterial species play.
“The [findings] that they have are correlational,” said Villapol, adding that the study is currently limited due to its small sample size and lack of control samples.
Aziz Zafar is now a graduate student at Columbia University.
Craig Sachson, Columbia University
Ay agreed, adding that this is information from only one type of sport and no female participants. He also noted the logistical difficulties of having a control group of football players. “We can't just tell them, ‘You are not going to be in team throughout the season and put them aside,’” he explained.
Belanger noted that while the sample size is small, they provided a number of fecal samples for analysis. “This is a pilot study,” he said, adding that they are now extending the study to a larger number of participants.
Ay is hopeful that such studies with larger sample sizes could help identify biomarkers for head impacts. “It could probably be a simple way to detect concussion or head impacts from just using fecal samples,” he said.
Belanger agreed, and added, “We think of this as a study that opens a really neat new window to go through to ask further questions.”
- Soriano S, et al. Alterations to the gut microbiome after sport-related concussion in a collegiate football players cohort: A pilot study. Brain Behav Immun Health. 2022;21:100438.
- Nowinski CJ, et al. 'Subconcussive' is a dangerous misnomer: Hits of greater magnitude than concussive impacts may not cause symptoms. Br J Sports Med. 2024;58(14):754-756.
- Pelland ZJ, et al. Non-concussive head impacts sustained during American football correlate with changes in gut microbiome diversity and composition. PLoS One. 2026;21(5):e0345651.
