More Miles, More Gut Trouble?

If you’ve ever trained for a marathon or ultramarathon and found yourself sprinting for the porta-potty afterward, you’re not alone. GI drama is a well-known companion of long-distance events. And now, a new study is raising eyebrows (and some colonoscopes) about whether extreme mileage might actually increase the risk of precancerous colon polyps.

At the 2025 ASCO Annual Meeting, oncologist Dr. Tim Cannon and colleagues at Inova Schar Cancer presented a small but striking study: among 100 elite runners - each with at least five marathons or two ultramarathons under their belts - 15% had advanced adenomas (precancerous growths) and 41% had at least one adenoma. That’s far higher than the ~1-2% rate typically seen in healthy adults of similar age.

The researchers suspect a link between exercise-induced gut stress - aka runner’s colitis - and these findings. Repeated blood shunting away from the intestines during endurance events may cause ischemia (temporary oxygen loss) and micro-injury to the colon. Over years of high-volume training, those tiny hits might add up.

This isn’t a new idea. The Science behind the Runner’s Runs is well documented. 

Even in healthy young adults, intense exercise in extreme heat (even stop-and-go sprints over just 3-4 miles) can trigger ischemic colitis. Studies report exercise-induced gastrointestinal (GI) symptoms in up to 70% of endurance athletes.

So yes, that stomach cramp isn’t just your gel packet revolting; your colon might actually be gasping for air.

Wait, Isn’t Exercise Supposed to Be Good for You? Absolutely. Decades of evidence, including a large randomized trial in NEJM (Courneya et al., 2025), shows exercise improves survival in colon cancer survivors. Moderate, consistent activity is a cornerstone of cancer prevention.

The Inova study doesn’t suggest jogging a few miles a week will hurt you - it’s zeroing in on ultra-endurance lifestyles, where pounding out 40+ miles a week is normal and multiple marathons are a badge of honor. (Because apparently 26.2 miles once wasn’t enough of a flex.)

Exercise remains one of the best things you can do for your health, but like any powerful intervention, more isn’t always better. Science is still catching up on what happens when you treat your body like a mileage sponge. For now, lace up, enjoy your runs, and listen to your gut - literally. After all, nobody brags about a Personal Record in their colonoscopy prep. 

REFERENCES and Notes

Timothy Lewis Cannon, Bonomelli S, Swain WR, Kaltman RD, Mani H, Xia M, Randall J, Wang H, Harnden I, Donet JA, Nguyen VA. Risk of pre-cancerous advanced adenomas of the colon in long distance runners.et al. Risk of pre-cancerous advanced adenomas of the colon in long distance runners. JCO 43, 3619-3619(2025). DOI:10.1200/JCO.2025.43.16_suppl.3619

Vujasinovic M, Omae M, Panic N, Fjellgren E, Bloch N, Kikec Z, Grasselli M, Lindberg G, Löhr JM, Baldaque-Silva F. Gastrointestinal bleeding in long-distance runners: a systematic review. Eur J Gastroenterol Hepatol. 2025 Jun 1;37(6):691-701. doi: 10.1097/MEG.0000000000002931. Epub 2025 Apr 29. PMID: 39976001.

Courneya KS, Vardy JL, O'Callaghan CJ, Gill S, Friedenreich CM, Wong RKS, Dhillon HM, Coyle V, Chua NS, Jonker DJ, Beale PJ, Haider K, Tang PA, Bonaventura T, Wong R, Lim HJ, Burge ME, Hubay S, Sanatani M, Campbell KL, Arthuso FZ, Turner J, Meyer RM, Brundage M, O'Brien P, Tu D, Booth CM; CHALLENGE Investigators. Structured Exercise after Adjuvant Chemotherapy for Colon Cancer. N Engl J Med. 2025 Jul 3;393(1):13-25. doi: 10.1056/NEJMoa2502760. Epub 2025 Jun 1. PMID: 40450658.

Cha S, Kwon BS, Hong N, Park JS, Byun SK, Choi SC, Kim YS. Ischemic Colitis Associated with Rhabdomyolysis and Heat Stroke after an Intense Exercise in Young Adult. Korean J Gastroenterol. 2019 Aug 25;74(2):115-118. doi: 10.4166/kjg.2019.74.2.115. PMID: 31438663.

https://www.inovanewsroom.org/press-release/2025/08/groundbreaking-inova-study-finds-potential-link-between-long-distance-running-and-colon-cancer/

Summary of the press-release comment thread:

• Personal stories & thanks: A marathon trainee (stage III colon cancer with BRAF mutation) and others thank Inova for investigating; several endurance athletes are now reconsidering training or seeking screening.

• Scope beyond running: Ultracyclists and triathletes ask whether the signal is from running mechanics (impact/ischemia) or endurance-sport commonalities (high-sugar fueling, fiber restriction, long efforts).

• Methodology concerns: Readers question the cited “expected 1–2%” baseline for advanced adenomas (ask for contemporaneous controls), call out small sample, no control group, and urge comparisons with fit and average peers.

• Timing/context questions: One commenter wonders why this is being detected now (post-COVID era) and suggests caution in public messaging to avoid undue alarm while encouraging screening for ultra-athletes.

• Media amplification: Several aggregator articles echo the press release; one commenter links to potentially conflicting evidence in NEJM (no details discussed in-thread).

• Net sentiment: Interest and cautious concern, with strong support for earlier evaluation of symptomatic runners and for larger, controlled follow-up studies before drawing causal conclusions.

https://www.reddit.com/r/science/comments/1nf8uod/study_finds_potential_link_between_longdistance/

Summary of the r/science comment thread:

Headline numbers (from the press release/study summary): commenters highlight that 15% of the 100 endurance runners (ages ~35–50) had advanced adenomas and 41% had any adenoma; average age 42.5 (younger than routine screening). Many find this “shocking.”

Who counted as “long-distance”: people who’d done ≥5 marathons or ≥2 ultramarathons—i.e., very high-volume runners, not casual 5–10K folks.

Big caveats (most-upvoted critiques): tiny, single-center cohort; no control group; wide CIs (e.g., the 15% could be ~8–23%); likely selection/volunteer bias (e.g., ~30% reported blood in stool; among those with advanced adenomas, ~53% reported post-run bleeding). Several users note it appears to be an abstract/press release rather than a fully peer-reviewed paper yet.

Anecdotes abound: multiple stories of very fit runners (some in their 30s–40s) diagnosed with colon cancer; others say such cases are still uncommon in clinical practice.

Hypothesized mechanisms:

• Ischemia/blood-flow shunting during prolonged exertion (exercise-induced ischemic colitis), repeated micro-bleeds/micro-tears, and mechanical jostling/impact of the colon.

• Sympathetic surge (adrenaline/noradrenaline) diverting blood from the gut.

• Diet/exposures common to endurance sports: high sugar/gel use, artificial colors/sucralose, processed supplements, heavy traffic pollution/particulates, microplastics, asphalt dust.

• Genetic predisposition/selection for people who excel at endurance.

Comparisons/questions: Could similar patterns exist in cyclists (prostate issues from prolonged pressure) or other endurance athletes? What about walking (most think benefits remain).

Evolution debates: back-and-forth on whether humans “evolved to run long distances” (persistence hunting) vs. arguments that extreme marathon/ultra training is not ancestral nor necessarily healthy.

Practical notes repeated by clinicians/runners: rectal bleeding is not normal; screen at 45 (earlier if symptoms or risk factors). Don’t over-interpret a small, preliminary study; larger controlled studies are needed before drawing causal conclusions.
Evolution debates: back-and-forth on whether humans “evolved to run long distances” (persistence hunting) vs. arguments that extreme marathon/ultra training is not ancestral nor necessarily healthy.

Practical notes repeated by clinicians/runners: rectal bleeding is not normal; screen at 45 (earlier if symptoms or risk factors). Don’t over-interpret a small, preliminary study; larger controlled studies are needed before drawing causal conclusions.

==

In fitness or sports, PR stands for personal record, PB (more commonly used in Canada) is personal best. Runners are using the terms PR and PB somewhat interchangeably.

From Step Counters to Gut Health Co-Pilots

Many of us wear tiny research labs on our wrists, fingers, and even shoes. These devices quietly track our steps, heartbeats, and sleep cycles. But the future of wearables isn’t just counting steps, it’s building personalized health co-pilots: adaptive, AI-powered systems that understand your unique rhythms and predict problems before they happen. For people with chronic gastrointestinal (GI) conditions like IBS, this shift could be transformative.

Recognizing this potential, the Health Secretary recently unveiled a nationwide initiative to promote wearable adoption. Announced on June 24 as part of the ambitious “Making America Healthy Again” agenda, the campaign aims to encourage every American to integrate these technologies into their daily lives.

A recent review highlights how wearable devices, from smartwatches to sensor patches, are already being used to monitor IBD activity, predict flares, and track biomarkers like fecal calprotectin and C-reactive protein. Future applications may include ingestible sensors, microbiome monitoring, and machine learning-driven early disease detection. Similarly, advances in acoustic sensing are turning bowel sounds into a diagnostic tool for IBS. Miniaturized microphones, AI models like convolutional and recurrent neural networks, and portable recording devices are bringing continuous, objective GI monitoring closer to reality.

But there’s a deeper layer emerging beneath these devices: Network Medicine (NM). NM maps disease as disruptions in interconnected molecular and physiological networks rather than single gene or biomarker abnormalities. By treating diseases like IBS as network-wide phenomena, NM provides a framework for understanding how gut inflammation links to immune responses, microbiome shifts, and even stress hormones. When combined with AI, especially deep learning, NM allows researchers to integrate massive multi-omic datasets (genomics, proteomics, metabolomics) with wearable device streams, revealing subtle, individualized signatures of disease progression or recovery. This fusion moves beyond simple symptom tracking, creating biologically grounded, predictive health models.

Similarly, NM’s predictive networks must adapt dynamically to individual variability. Researchers are working on cross-user adaptive AI and network-aware modeling that runs efficiently on-device, preserving privacy while continuously refining predictions. Recent systematic reviews of large language models in healthcare - echoing earlier analyses of AI’s underutilization in biomedicine - underscore this theme: despite rapid advances, there are persistent gaps between benchmark performance and real-world usability, emphasizing the need for dynamic, evaluator-aware frameworks to guide safe clinical adoption.

Imagine a wearable ecosystem that does more than log symptoms - it connects the dots through network science: a smartwatch detecting subtle heart rate variability, a ring tracking skin temperature trends, and an ingestible sensor analyzing gut pH. Integrated with NM-driven AI, these signals could identify emerging disease network perturbations and predict a flare-up 48 hours in advance, guiding personalized diet tweaks, medication adjustments, or stress management before symptoms strike. Bowel sound analysis, combined with unobtrusive “toilet-lab” technology could replace tedious food diaries with objective, automated insights, creating a continuous and rich feedback loop between the body and the wearer.

The leap from step counters to gut health co-pilots isn’t just a technical upgrade; it’s a paradigm shift -from reactive care to proactive, precision health. By merging wearable technology with AI and NM, supported by seamless in-home lab testing, we’re approaching a future where chronic GI condition management is informed by both real-time physiological data and deep network-level understanding of disease. With careful design, strong privacy safeguards, and adaptive AI, wearable tech could evolve into indispensable tools that don’t just monitor illness but actively shape health outcomes.

REFERENCES

Nicholas GO, Faith LI, Jeric MC, KO O, Kelvin KF, Seung-Min PA, Christopher HT, Sunny HW. Acoustic sensing and analysis of bowel sounds in irritable bowel syndrome-recent engineering developments and clinical applications. Sensors and Actuators A: Physical. 2025 Jul 22:116910.

Harindranath S, Desai D. Wearable technology in inflammatory bowel disease: current state and future direction. Expert Review of Medical Devices. 2025 Feb 1;22(2):121-6.

Irene S. Gabashvili Evaluating General-Purpose LLMs for Patient-Facing Use: Dermatology-Centered Systematic Review and Meta-Analysis medRxiv 2025.08.11.25333149; doi: https://doi.org/10.1101/2025.08.11.25333149

Erturk E, Kamran F, Abbaspourazad S, Jewell S, Sharma H, Li Y, Williamson S, Foti NJ, Futoma J. Beyond Sensor Data: Foundation Models of Behavioral Data from Wearables Improve Health Predictions. arXiv preprint arXiv:2507.00191. 2025 Jun 30.  https://arxiv.org/abs/2507.00191

Cai Y, Guo B, Salim F, Hong Z. Towards Generalizable Human Activity Recognition: A Survey. arXiv preprint arXiv:2508.12213. 2025 Aug 17. https://arxiv.org/abs/2508.12213

Harvard dropouts to launch 'always on' AI smart glasses that listen and record every. TechCrunch Aug 20, 2025 conversation. https://techcrunch.com/2025/08/20/harvard-dropouts-to-launch-always-on-ai-smart-glasses-that-listen-and-record-every-conversation/