Running offers some great health benefits: a healthier heart, improved mood, stress relief, self-confidence, weight management, and more. But you probably haven’t heard how endurance running can harm your gut health, and your overall health, over time.
In this blog, I’ll explain how high-volume long-distance running, such as frequent marathons or ultrarunning, can negatively impact your gastrointestinal (GI) tract and well-being, and what you can do about it. We’ll also briefly cover how even shorter distances can cause GI upset that can negatively affect well-being.
This blog will discuss the following:
- What is high-volume endurance running?
- Gastrointestinal distress & damage
- Post-run GI upset and appetite changes
- Reliance on processed foods
- Mental stress
- Nutrition & lifestyle tips to protect gut health for endurance runners
Don’t worry, I’m not going to tell you to stop running! I still run every week. However, I will explain why you may want to think twice about your high training volume and racing load for the sake of your current and future health, plus provide some tips for staying healthy if you do decide to continue running those long miles.
What is Long-Term, High-Volume Endurance Running?
Most studies that have found problems with gut health, referred to as exercise-induced gastrointestinal syndrome (EX-GIS), have been with runners who regularly run marathons, ultramarathons, and long-distance triathlons. There is not a set standard for how much or how frequently a person must run to cause problems, because each person’s situation is unique. But it does appear that runners who consistently run and race long miles like marathons and above are the most likely to experience chronic gut health problems.
Short-distance running does not appear to be as problematic, such as the 5k, 10k, or even half-marathon distance. So, GI upset or poor gut health may not apply as much to the person who runs just one marathon or one ultra-distance event in their life, for example.
But we do know that temporary changes to the gut can happen in as short as 10 minutes after starting your run. This means that even running short distances may have a negative impact for some people, such as myself.
In my personal running experience, stomach upset occurs in as little as 6 miles to a half marathon distance. In fact, it was during my last half-marathon training that I experienced all of the problems we will cover in this blog, which led me to into a research deep-dive on this topic. To learn more about my discoveries beyond this blog, check out my Runner’s Guide to Reducing Gastrointestinal Symptoms online course with PDF reference guide.
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4 Ways Endurance Running Can Harm Your Gut Health & Overall Wellbeing
Let’s dive into how endurance running has the potential to negatively impact your health over time and what you can do about it.
#1: Gastrointestinal Distress and Damage
Long-distance running is often praised for its cardiovascular benefits, but it can also present challenges for gut health that are frequently overlooked. While the thrill of crossing that finish line can be enticing, it’s essential to consider the potential downsides of pushing the body to its limits.
The repetitive impact of running can create mechanical stress on abdominal organs, exacerbating symptoms like bloating, cramps and diarrhea for many runners. This discomfort can be a significant distraction during training and races, detracting from the overall experience.
I have dealt with some of these issues during multiple running races and triathlons which has forced me to slow down and not perform as well as I knew I could.
Endurance exercise also reduces blood flow to the gastrointestinal (GI) tract because your body is redirecting the blood that would normally go to the intestines for digestion to your working muscles.
For some people, this lack of blood flow can lead to cramps, vomiting, diarrhea, bloody stools, or gut permeability or “leaky gut”. While the term “leaky gut is less scientific, I will use it for the remainder of the blog because it’s easier to understand.
Leaky gut is essentially openings between the intestinal cells that shouldn’t be there which allow toxins and substances from the GI tract into your blood stream where they shouldn’t be. This creates an immune system response that can cause immediate discomfort or, over time, could contribute to low-grade chronic inflammation and health problems such as auto-immune diseases or irritable bowel syndrome.
There can also be temporary – or lasting – damage to the microvilli in the intestines which is important for nutrient absorption. If the microvilli are damaged, you won’t absorb as many nutrients, which can impede recovery after running, contribute to unwanted weight loss, and cause nutrient deficiencies such as iron, vitamin B12, or calcium.
If the effort is strenuous enough, such as ultra-marathons, damage and inflammation can show up as bloody stools. This should be a sign that something is wrong and that training and/or diet should adjusted. It’s not “just one of those things” runners deal with.
While the intestinal damage is typically temporary for most runners, if it’s frequent enough or stressful enough to the body, it could become more lasting damage with health consequences, though this is an area needing more scientific research to determine long-term affects.
For some people with conditions like irritable bowel syndrome (IBS) or inflammatory bowel disease (IBD), this can worsen their symptoms. While science is lacking, it is possible that it could also aggravate untreated celiac disease. Stress in the gut exacerbates ongoing symptoms and can make chronic inflammation, pain, and/or weight loss from poor nutrient absorption even worse.
Usually when someone is struggling with active and symptomatic IBS or IBD, it is advised to do more calm exercise that isn’t so strenuous or hard on the gut to help ease symptoms and inflammation.
I’ve had chronic gut issues for many years, and even though I finally figured out the root causes and had found significant relief from changing my diet, I still had ongoing GI upset during my last half-marathon training for the reasons mentioned above. Not only during running, but more so after running and on a daily basis, such as stomach pain and bloating after eating.
For those of us who live with chronic GI symptoms, even if it’s not life-threatening, you know how incredibly frustrating and mentally stressful it can be!
TIP: If you experience these types of symptoms regularly, you may want to visit a gastroenterologist or dietitian who works with GI disorders, or at least consider reducing your running load to allow your gut to rest and heal.
#2 Post-Run Changes in Appetite and Muscle Loss
It can take several hours or even days for the GI tract to get back to its normal state after long or intense exercise. If you’ve run a long-distance event like an ultra marathon, you may have experienced ongoing digestive upset for quite a while after the event due to inflammation and leaky gut. During this time, you may do best with easy-to-digest, bland foods.
Even without stomach upset, changes in appetite can occur, further complicating recovery. Many athletes experience a drop in appetite after running. If you don’t eat enough calories, protein and carbohydrates after intense training or racing, it is harder for the body to repair itself.
This lack of adequate nutrition can increase the likelihood of injuries, slow down recovery times, make it hard to stick with a training schedule which can hinder performance, and eventually lead to muscle loss.
This is exactly what I dealt with during my last half-marathon training. My appetite was horrible and at times I had to force myself to eat at times, often foods that weren’t healthy, just because they were some of the only foods I could tolerate.
As training went on, I had unwanted weight loss, but also started noticing changes in my muscle tone and structure. The muscle I had worked SO hard for over many years was slowly changing to a more “wasted” and skinny look due to not being able to tolerate enough calories to keep my msucle on with the demands of endurance exercise.
When you don’t have fuel before, during, and after running, your body will eventually turn to amino acids – or protein – that is stored in muscles, which is what causes muscle loss.
Without sufficient caloric intake to meet the high demands of training, the body may begin to break down muscle for energy, undermining the very strength and endurance that runners strive to build.
TIP: Even if your appetite tanks right after exercise, try to focus on eating some type of carbs and protein immediately after your run (for specific amounts, check out my Runner’s Guide Nutrition Course). Then increase your calorie intake in the days after to help make up for any deficits. You may also want to eat a bit extra before exercise to ensure your body has plenty of available glucose to utilize.
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#3 Reliance on Processed Foods in Endurance Running
Another concern with running and gut health is that long-distance runners often rely heavily on energy gels, sugary sports drinks with artificial flavors and colors, and quick sources of carbohydrates that are high in sugars and low in nutritional value.
While these quick sources of energy may be necessary during long runs, they can also contribute to imbalances in the gut microbiome and lead to digestive discomfort. Many energy products are highly processed and contain added colors, preservatives, maltodextrin, artificial sweeteners, and chemicals that disrupt the gut microbiome and can contribute to chronic leaky gut and inflammation.
Some also contain high amounts of fructose which IS an important carb source alongside glucose when running long distances, but it can be hard for some people to digest. Fructose can be poorly absorbed and fermented by gut bacteria, which are primary causes of bloating, diarrhea, and general GI upset.
The daily carbohydrate needs of runners can be much higher than non-athletes, so we often turn to simple and easy-digesting carb sources like white bread, candy, pastries, sodas, and other highly processed, low-fiber foods. While these foods can serve a purpose in training and racing, they also promote the growth of bad bacteria and reduce the amount of good bacteria in the gut. Over time, this may inhibit nutrient absorption, damage the intestinal wall and play a role in leaky gut, negatively impact the immune system, and play a part in the development of diseases.
Additionally, a lack of variety and fiber in the diet can prevent runners from obtaining essential vitamins and minerals, which are crucial for overall health, energy, and recovery.
See tip below on eating a healthy diet.
#4 Mental Stress of Endurance Running and Gut Health
While the physical stress of long-distance training and racing is obvious, our quests for personal bests, podiums, and race medals can also create mental stress that poses challenges for gut health.
This is because a connection exists between the brain and the gut referred to as the gut-brain axis. When we are mentally stressed, it can cause increased gastrointestinal distress and cause imbalances in the good and bad bacteria in the gut.
Training and racing often bring on psychological strain whether it’s from scheduling and time commitments, early mornings, race planning, traveling, or a competitive mindset and need to succeed.
These factors may contribute to issues such as anxiety and depression, which disrupt healthy digestion and lead to a cycle of inflammation and GI problems. A stressed gut can, in turn, affect mood and performance, creating a detrimental feedback loop that makes it even harder to train effectively.
Personally, knowing I can’t miss certain runs, have to re-prioritize plans, need to get up early for a long run even if I’m tired, and the drive to perform well can add unnecessary stress and anxiety to my life for something that is intended to be healthy, fun and social.
If your career and livelihood isn’t depending on your run success, it may be worth taking a break once in a while to stepping back to gain perspective and determine if running has become more important than staying mentally, emotionally, and physically healthy.
What Happened to My Gut Health After Reducing My Run Mileage?
After my last half marathon was done, I reduced my endurance running distance on weekends. Not long after, my ongoing stomach upset and poor appetite improved dramatically and I started putting more effort into rebuilding lost muscle and adding back healthy weight that I’d lost during the process.
My gut health is now MUCH better. If you’ve ever struggled with poor digestion, you know that feeling normal can make ALL of life better!
The mental and physical stress, gut issues, and muscle loss during my previous race training led me to the point where I’d prefer not to take on any long endurance running events. Since my main passion is shorter-distance triathlons, this works well for me because neither swimming or cycling are as hard on the gut as running. So, I can still enjoy endurance sport and running shorter distances like 5-10 miles without the gut health concerns.
But what if running is YOUR passion? Am I telling you to hang up your shoes?
No! I know how passionate runners are about our sport, and running can be an excellent way to stay fit, release stress, and build physical and mental perseverance when done with moderation and proper nutrition.
However, I would advise that if you run multiple marathons, Ironman triathlons, and/or ultra marathons per year to pay extra close attention to your digestion and gut health, use the tips below, and work in some months of reducing distance and/or cross-training with things like cycling or strength training.
So let’s look at some tips you can use to keep your GI tract and digestion as healthy as possible.
Tips for Endurance Runners for Better Gut Health
Here are some tips to keep in mind if you are struggling with issues like gut health but want to continue endurance running.
- Balance your training and racing efforts. Consider doing only a few long-distance events per year, especially if you do ultra-marathons or Ironman triathlons. This can benefit not only gut health but keep stress and inflammation down for overall health. You could also mix in some shorter distances that aren’t so taxing to train for, like a 10k or sprint triathlon. You could also consider new challenges such as cycling, rowing, mountain climbing, hiking, etc to work your body in new ways while still enjoying exercise and the outdoors.
- Include strength training. Not only will it help you maintain muscle mass which is essential for healthy aging, but it can make you a faster runner and reduce chance of injury. This type of exercise can also be beneficial for the gut microbiome.
- Check in with your gut. How is your digestion? Do you often have GI upset when running? Do a lot of foods cause bloating, pain, gas, etc? Any blood stools after races? You may want to pull back on your training for a time to allow your gut to heal. You may also need to look at the foods you eat to see if certain foods are causing problems. If this is an issue, check out the Runner’s Guide to Reducing Gastrointestinal Symptoms course, or contact me directly for 1:1 help addressing dietary issues.
- How is your recovery? Do you have rest days? Do you take time to relax, stretch, lay on the couch, or do other calming activities to let your muscles and intestines heal?
- Hydrate and eating adequately during runs. Dehydration can make GI upset worse, and eating frequently can help keep blood flowing to the intestines to help reduce leaky gut, damage, and inflammation.
- Avoid NSAIDs. Non-steroidal anti-inflammatory drugs like Ibuprofen can make GI upset worse and contribute to the problems discussed in this blog, not to mention it can damage organs like the liver with prolonged or high-dose use.
- Eat a healthy diet. Try not to rely so much on highly processed foods and refined carbs. If your stomach can tolerate it, mix in some dried fruit, honey or maple syrup, or chia and fruit puree pouches to provide some of your carbs. Outside of training, try to keep your diet high in fiber from real, natural foods with plenty of vegetables, fruit, and whole grains. Make sure you also eat healthy fats and protein to keep your muscles, hormones, and cells happy.
- Try interval training. If you don’t already do interval training, it’s a great way to improve speed and fitness, but can be done is much shorter training sessions so you don’t have to spend so much time pounding the pavement.
- Certain supplements like L-glutamine, omega-3 and probiotics may also be helpful for some people, which I can address in a future video, but I do prefer to recommend supplements on a person-by-person basis.
- Check your poop. If you’re regularly having diarrhea, loose stools, constipation or blood in your stools, go see your doctor – specifically a gastroenterologist. These can all be indicators of GI diseases and should be checked on to rule out any serious conditions that may get worse with excessive running.
Conclusion: How Endurance Running Can Affect Gut Health
Incorporating these strategies can help mitigate adverse effects and promote a healthier, more enjoyable running experience. Ultimately, finding a sustainable approach that prioritizes both performance and well-being is crucial for a long-term love of the sport. Balance is best when it comes to long-term health, not constantly pushing your body to the limits.
If you’d like more help with keeping your gut and body healthy as a fellow athlete, you can contact me to learn more about 1:1 nutrition counseling or check out my YouTube channel where I often post videos about running nutrition.
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