A new study from Colgate University found that head impacts that don’t cause concussion symptoms are still linked to measurable shifts in the gut microbiome of collegiate football players — opening a new frontier in sports health research.
Football players absorb hundreds of head impacts each season that never result in a concussion diagnosis — no headaches, no dizziness, no clinically detectable symptoms. But a new study suggests those hits may not be entirely without consequence. Researchers at Colgate University led by Ahmet Ay and Kenneth Douglas Belanger found that even sub-concussive impacts are associated with notable changes in the gut microbiome, the vast community of bacteria and microorganisms living in the digestive system.
The study, published May 6 in the open-access journal PLOS One, is believed to be the first to directly examine the relationship between head impacts and gut microbiome composition. Six NCAA Division I football players were tracked across an entire competition season, beginning in preseason training, giving researchers a detailed window into how on-field activity shapes what’s happening inside the body.
“As far as we are aware, this is the first study to examine connections between head impacts and the composition of the gut microbiome – the complex community of bacteria and other organisms within the digestive system,” Belanger, the Russell Colgate Distinguished University Professor of Biology at Colgate University, said in a news release.
How the Study Worked
Tracking the intersection of football and gut health required a sophisticated multi-layered approach. Players wore GPS units during practices and games to monitor movement and exertion, while helmet-based sensors recorded every head impact across the season. Participants provided fecal samples regularly — 226 samples in total — which were analyzed for microbial diversity and composition. After each sample collection, players also filled out lifestyle questionnaires covering factors like diet, sleep, stress levels, and exercise intensity.
That level of detail allowed the research team to account for 15 potentially confounding variables before drawing conclusions. Even after controlling for those factors, the data pointed in a consistent direction: head impacts were associated with gut microbiome changes.
What Changed in the Gut
Within two to three days following a substantial head impact, researchers observed measurable shifts in microbial diversity. Certain bacterial groups — including the order Coriobacteriales, the family Prevotellaceae, and the genus Prevotella — tended to decrease in abundance. Meanwhile, the genus Ruminococcus increased. In prior research, similar patterns have been associated with brain injury and inflammation, making these microbial shifts potentially meaningful beyond the digestive system alone.
The gut microbiome didn’t just respond in the short term. Mathematical modeling of the season-long data suggested that the cumulative effects of repeated non-concussive impacts were likely associated with broader shifts in the microbiome over time — not just a single spike after one big hit, but a gradual drift across weeks and months of play.
“Our results provide evidence that even head impacts that do not result in a concussion or other reported symptoms may influence the microbes present within the gut, both in the short- and longer-term. Determining what causes these changes and whether they have a positive or negative influence on recovery from head injury will require further investigation,” Belanger added.
Why It Matters
The gut-brain axis — the bidirectional communication network between the digestive system and the central nervous system — has gained significant scientific attention in recent years. Research has shown that the gut microbiome plays a role in regulating inflammation and the neuroimmune system, meaning disruptions there can potentially influence brain health and vice versa. Prior studies established that full concussions can alter the gut microbiome, but whether sub-concussive hits had any similar effect was unexplored territory.
For the roughly 1 million high school athletes and tens of thousands of college players who participate in American football each year — experiencing anywhere from 100 to 1,000 head impacts per season — the implications are significant. If even symptom-free hits are shifting gut microbial communities in ways that mirror patterns seen in brain injury, it raises questions about long-term health outcomes that extend far beyond what current concussion protocols track.
“Our research highlights the importance of thinking integratively about the interactions between the gut and the brain. We are only beginning to scratch the surface in our understanding of how these complex organs and organ systems communicate with and affect each other,” Belanger added.
Student Researchers at the Center of the Work
The study is notable not just for its findings but for who conducted it. Zachary Pelland, a Colgate football player, served as co-first author — meaning he was both a subject of the research world the paper describes and one of its key investigators. Co-first author Aziz Zafar also contributed to the project as an undergraduate researcher.
“After having only heard of the complicated interplay between neuronal inflammation and the gut microbiome, I found it to be such an exciting scientific experience to explore that interplay in the context of head impacts,” Zafar said in the news release.
“It has been an amazing privilege to work so deeply on a personally and scientifically meaningful project which could not have happened without immeasurable support across academic departments, athletics, administration, and alumni at Colgate University,” Pelland added.
Limitations and Next Steps
The researchers are careful to note what the study cannot yet tell us. With only six participants and no control group, the findings establish correlation — not causation. A broader study with more players, a comparison group of non-contact sport athletes, and biological measurements that can pinpoint mechanisms would be needed to determine whether these microbial shifts are harmful, neutral, or even part of the body’s adaptive response to physical stress.
Still, the study provides a compelling proof of concept that the gut microbiome responds to head trauma even below the threshold of clinical symptoms — a finding that could reshape how researchers and clinicians think about athlete health monitoring in contact sports.
Source: PLOS