IBS and High-Intensity Exercise: Your Guide to Train Smart Without the Gut Flare-ups

Are you an avid exercise lover? Do you also have Irritable Bowel Syndrome (IBS)? Then this article is for you! 

If you’ve spent any time on social media in the IBS and gut health space, you’ve probably seen claims about how high-intensity exercise is something to be avoided if you want to manage your IBS symptoms and prevent flare-ups. You’ve heard that it “spikes your cortisol” and can even wreak havoc on your “hormone balance”.

Perhaps you’re a little happy about this narrative (because these workouts ARE tough!). Or perhaps, you’re torn, because you know they make you feel mentally good, may help with body composition goals like reduction in body fat, and you’ve heard there are also certain health benefits?

Well fear not, there is a lot to unpack here and the answer about whether you should or shouldn’t avoid high-intensity exercise when you have IBS may surprise you! We will also get into some low FODMAP fuel examples for when you do engage in those types of sessions. 

What is High-Intensity Exercise?

High-intensity exercise refers to physical activities performed at a level of effort that is close to your body’s maximum capacity. This usually corresponds to ≥90% of maximal oxygen uptake or >75% of your maximal power. There are some conflicting opinions about what exactly high-intensity exercise means, however, this is a generally agreed-upon definition. 

To bring this out of the science realm and help the everyday person understand if they are engaging in true high-intensity exercise, it’s common to use the Rate of Perceived Exertion (RPE) scale. The RPE scale can help you to qualify effort levels in order to achieve low vs. moderate vs. high-intensity exercise in a workout session. Your RPE refers to how hard you think you’re pushing yourself during exercise. The RPE scale was developed in the 1960s by Gunnar Borg, a Swedish researcher. 

The simplified version looks like this, which many personal trainers and coaches use with their athletes:

It is subjective but is based on a few elements you can take into account to assess your level of exertion, including: 

• How fast/ hard you’re breathing
• How quickly your heart is beating 
• How fatigued/tired your muscles are
• How much you are sweating

With this in mind, true high-intensity exercise involves pushing your body to near-maximal effort during work periods (RPE 8-10). As these intensities are hard to sustain for a long period of time, we would use shorter work durations (10-60 seconds) and adequate recovery (1:1 or 1:2 work-to-rest ratios) in these workout sessions. 

Each person has a different fitness level and training history, so the actual parameters for high-intensity will vary from one person to another. Let’s dive a little deeper into the details.

Executing High-Intensity Exercise Properly & Safely

There is often some confusion around high-intensity exercise, and quite often the exercises are not executed properly. Here are some key points here to help you understand whether you are truly engaging in high-intensity exercise, and how to do it safely. 

Keep Them Brief

The great thing about high-intensity workouts is that they are short and sweet. True high-intensity sessions are kept brief but focused—20-30 minutes is typically sufficient. 

Avoid the Moderate Intensity Rut

A concern is falling into the “mid-intensity” range where the training effect is significantly diminished. True high-intensity efforts must be short and performed near-maximally (RPE 8-10). If you feel like you could sustain the work longer, it’s likely not high-intensity. 

In order to work at or close to your maximum capacity, the number of intervals (or repetitions) you complete should only be so many that you can actually sustain at the same intensity level. Monitor performance—if you cannot sustain intensity across intervals, consider adjusting your rest or overall volume (i.e. number of intervals).

Aerobic Fitness & Strength Base Is a Prerequisite

One should have a basic foundation of aerobic fitness and strength to get the most out of high-intensity work, to avoid potential injury.

Prioritize Proper Form & Rest

Intention towards excellent form is essential to maximize the training effect and minimize injury risk. As mentioned above, for high-intensity exercise we use shorter work durations (10-60 seconds) and adequate recovery (1:1 or 1:2 work-to-rest ratios). The idea is we want to recover well enough between sets to ensure execution with proper form at maximal effort. That said when your form breaks down, the set is over. Work with a coach or trainer to ensure you are doing your training properly. 

Examples of High-Intensity Workouts 

There are some varying definitions of high-intensity exercise, and they can take different forms including running, cycling, weight lifting and bodyweight training. Most people think of HIIT (aka high-intensity interval training) but this is not the only type of high-intensity exercise. 

Here are a few common examples: 

1. Sprint Training: Short, all-out running intervals, such as sprinting for 15-20 seconds followed by a minute of walking or easy jogging. 
2. High-Intensity Interval Training (HIIT): A workout style combining bodyweight exercises like burpees, jump squats, or mountain climbers in intense bursts (30–45 seconds) with brief rest periods (30-60 seconds). 
3. Cycling Intervals: Alternating fast pedaling at high resistance and slow recovery pedaling on an indoor or outdoor bike.
4. Heavy Weightlifting: Performing exercises like deadlifts, squats, or bench presses with heavy weights for low reps (i.e. 5 sets of 5 repetitions where at the end of each set, you can only do 1-2 more reps with good form).
5. Circuit Training: Combining multiple exercises with equipment (e.g., kettlebell swings, battle ropes, and medicine ball slams) performed back-to-back with minimal rest time.

What is Cortisol?

Now that we understand the basics of high-intensity exercise let’s explore its impact on the body’s stress response.

You probably know cortisol as the body’s “stress hormone.” Although this term may have a negative connotation, but cortisol is an important hormone that has various effects on different vital functions in the body. It mediates the stress response, supports mental alertness and focus, regulates metabolism and the inflammatory response, and affects immune function.

In normal physiological conditions (i.e., everything is working as it should), cortisol typically rises to its peak after waking and naturally falls throughout the day. If this correlates with a typical energy pattern for you, then this means you generally have a typical cortisol rhythm! 

It is when there is a loss of regulation of cortisol that can lead to various health issues and symptoms such as extreme fatigue, slowed metabolism, impaired immunity, and more. Let’s get into this more below. 

The Cortisol Controversy: When High-Intensity Exercise Gets Blamed

When it comes to high-intensity exercise, it is true that it increases cortisol. High-intensity exercise is a physical stressor that temporarily elevates cortisol to support energy production and fuel muscle activity. During intense workouts like sprints or heavy lifting, cortisol mobilizes glucose and fatty acids, helping maintain performance.

However, this should be a temporary elevation, which is both normal and actually beneficial in small doses. 

Problems arise when cortisol remains elevated for prolonged periods (aka after intense sessions and on off days), which can lead to:

• Muscle breakdown
• Reduced exercise recovery 
• Increased risk of overtraining
• Reduced/ weakened immune system 

So this does not mean you need to avoid high-intensity exercise altogether. Labeling it as “too stressful” on the body doesn’t capture the full picture; it’s about how you manage the overall stress load on your body. 

What are the Health Benefits of High-Intensity Exercise?

So you’ve made it this far, something tells me you’re likely intrigued by the idea of embracing high-intensity exercise in your IBS-friendly lifestyle. Well good news, you CAN do high-intensity exercise when you have IBS or gut issues (given you’re cleared by your doctor on any other medical concerns). And there are MANY health benefits of this type of training to boot! 

Properly executed high-intensity exercise challenges your cardiovascular system, builds strength, and improves endurance by engaging fast-twitch muscle fibers and triggering metabolic adaptations. While demanding, high-intensity workouts are short but efficient, allowing you to improve your physical fitness when combined with proper recovery.

One key benefit of high-intensity exercise is improvement in metabolic health. 

There is no universal definition of metabolic health, however, to be metabolically healthy generally includes having ideal levels of blood sugars, blood lipids (cholesterol and triglyceride), blood pressure, and also waist circumference . With this in mind, there is evidence that high-intensity exercise helps improve insulin sensitivity and blood sugar regulation, as well as reduce body fat levels. 

High-intensity workouts are also very time-efficient. As we mentioned they don’t usually last longer than ~30-minutes, which can be great for anyone looking to add 1-2 weekly workouts to support body composition change, without requiring a huge time commitment. 

We also know that IBS is linked with higher levels of anxiety and depression. high-intensity workouts can be both a mental as well as a physical challenge, so getting yourself through a tough workout can be a big accomplishment! This can help someone to improve their overall sense of confidence, improve their mood, and general outlook on life by proving they can accomplish difficult tasks. 

Is High-Intensity Exercise Bad for Gut Health?

Truthfully, there isn’t a lot of research done on those with IBS specifically engaging in high-intensity exercise. However, there is research demonstrating that high-intensity and prolonged strenuous exercise can cause a reversible impact on gastrointestinal integrity as well as the microbiome population. 

A 2021 systematic review showed that regular moderate exercise supports gut health, but prolonged or high-intensity sessions can increase permeability. However, as noted above this change is reversible and won’t necessarily contribute to poor gut health if the right conditions are met. 

For most healthy individuals, regular high-intensity exercise does not necessarily lead to poor gut health and may even improve it with proper recovery and nutrition. However, under certain conditions, it could contribute to gut issues over time.

How to Embrace High-Intensity Exercise Properly 

High-intensity workouts can be a part of your routine—even if you’re managing IBS and chronic gut issues—by adopting science-based strategies to keep the associated cortisol level increases short-lived and beneficial in small doses. 

We can help support a regular cortisol response from high-intensity exercise through the following considerations: 

1. Balance Your Training

Here’s the caveat: high-intensity exercise is NOT beneficial in excessive amounts. A little goes a long way, and for most 2-3 sessions per week is recommended. If you’ve never followed a structured exercise regimen, then starting with lower to moderate intensity would be best first, and building up to one high-intensity session per week. It’s best to work with a personal trainer to do this safely and properly. 

On the days you aren’t doing high-intensity exercise, this is where lower intensity sessions come into play (ie. 2-5 on the RPE scale). Having hard days sprinkled in with easier sessions allows your body to adapt as well as push hard in those hard workouts while getting adequate recovery between. Think easy runs, elliptical, or cycling (2-4/10 RPE) if you’re an endurance athlete, or doing less intense weight training like pilates or sessions with lower weights, and higher reps with rest between. 

2. Schedule Recovery & Rest Days 

This feeds off the point above. While we recognize that not everyone reading this is an athlete training at very high volumes, this point is for those who have a regular exercise regime and may think that more is always better. Having 1-2 rest days per week works best for most athletes and active individuals to let your body repair and absorb the effects of training. 

Active recovery options like yoga, light cycling or elliptical, or mobility work can reduce overall stress on your body on rest days while keeping you moving.

Sleeping well, engaging in mobility work, proper nutrition and hydration can help ensure you recover well between those hard sessions. 

3. Avoid Fasted Training (Especially if You Have IBS)

When it comes to hard workouts, sports guidelines recommend avoiding fasted training before intense sessions. Training “fasted” essentially means you haven’t consumed any form of food in a relatively extended period of time. For most people, this would occur if you woke up and did a workout in the morning before eating anything. 

This is shown to be even more crucial for female athletes, as training with low energy availability can lead to cortisol elevations that may negatively impact their reproductive hormones and system. 

How Fasted Training Impacts Your Gut… 

We know that high-intensity exercise is already a stress on the body, so we want to avoid adding more stress. Fasted training can increase the risk of digestive symptoms like bloating, cramping, and diarrhea for several reasons:

• Heightened Stress Response:
  • Training in a fasted state can further elevate our cortisol levels. This can negatively affect gut motility and permeability, potentially leading to symptoms like bloating and cramping. 
  • For all athletes, but especially if you have IBS, we want to avoid further exacerbating gastrointestinal symptoms! 
• Reduced Blood Flow to the Gut:
  • During exercise, blood flow is redirected away from the digestive system toward working muscles. In a fasted state, this effect may be amplified due to lower circulating energy availability, impairing digestion and absorption when the gut is challenged (e.g., during longer or intense training).
• Inflammation & Gut Permeability: 
• Prolonged or high-intensity exercise, particularly in a fasted state, can compromise the intestinal barrier. This is thought to increase the risk of endotoxins entering the bloodstream, which may trigger inflammation and lead to symptoms like bloating or diarrhea.
• Electrolyte Imbalances:
  • Fasted training without adequate hydration or electrolyte intake can disrupt the balance of salts in the body, increasing the risk of cramping and diarrhea.

4. Fuel Up Properly Before Your Sessions

Further, training at a high-intensity without fuel can hinder performance (prevent you from exercising maximally). This means you may not be getting into the high-intensity zone, and truly reaping the benefits.

Fuel up pre-workout with carbohydrates and easy-to-digest protein. A general guideline is ~0.5g of protein and carbohydrates per kilogram of body weight. Since high-intensity exercise reduces blood flow to the GI tract, having low FODMAP as well as low fiber and fat options is recommended before your training. 

Here are some easy examples for pre-workout fuel (low FODMAP):

• Protein Shake: Mix 25 grams of a low FODMAP protein powder with ⅓ cup (75 ml) oat milk, 1 cup (240 ml) water, and 1 tablespoon maple syrup. 
• Oatmeal: Have ½ cup (40 g) instant oatmeal with 1 medium-firm banana and ½ cup (100 g) lactose-free Greek yogurt or cottage cheese. 
• Toast + Egg Whites: Cook ½ cup (120 ml) egg whites and serve with 2 slices of low FODMAP toast and 1 teaspoon almond or peanut butter.

Aim to have these options around 60-75 minutes before your high-intensity workouts. 

You may also want to read: 

• Pre-Workout Nutrition and the Low FODMAP Diet
• Post-Workout Nutrition And The Low FODMAP Diet

5. Ensure You Are Eating Enough to Match Exercise Demands 

Avoid low energy availability: AKA eat enough calories, carbs, and protein to meet your demands. Undereating on a regular basis can cause cortisol spikes as well as muscle loss (which works against your goals!). Signs of low energy availability include poor recovery, increased cold and flu, reduced performance, and low mood. Work with a Dietitian who specializes in sports nutrition and digestive health to ensure you are meeting your needs. 

You may also want to read:

• Athletes with IBS: Eating for Optimal Recovery, Performance & GI Health

6. Be Mindful of Overall Stress Load

Get adequate sleep. This is the time your body spends on cell repair as well as central nervous system recovery. Guidelines generally suggest active adults aim for 8 hours per night, plus an additional hour for every hour of moderate to high-intensity exercise to help your body recover from the demands of training. 

Support your vagus nerve: which plays a role in calming your nervous system, by incorporating activities like deep breathing, meditation, or mindfulness practices.

You may also want to read:

• IBS and Stress Series: The Feel Good Life – A Methodology To Reduce Stress

More About the Cortisol & IBS Connection

As we discussed above, increased cortisol levels can increase the risk of digestive symptoms and that can be exacerbated by doing high-intensity exercise when fasted or under fuelled. We also know that higher levels of mental stress and conversely cortisol levels are linked with increased IBS symptoms. 

Considering that stress can negatively affect IBS symptoms, it’s no surprise that managing overall stress is helpful for IBS. A recent (2023) systematic review with meta-analysis showed that stress management may be beneficial for patients with IBS regarding the short-term reduction of bowel and mental health symptoms. However, there was a lack of good quality randomized controlled trials (RCTs) with more than 6 months of follow-up so the long-term benefits weren’t conclusive (although we can assume that stress management is generally always a good thing for your digestive health and IBS!)

A 2022 systematic review showed that those with IBS may have altered stress reactivity, however, it wasn’t clear whether it was due to the IBS itself or the high prevalence of psychiatric conditions (anxiety, depression) in the IBS population.

Looking at cortisol levels a little deeper, a recent meta-analysis of 85 studies investigating the relationship between hypothalamic-pituitary-adrenal (HPA) axis activity and functional somatic disorders (FSDs)—including chronic fatigue syndrome (CFS), fibromyalgia (FM), and irritable bowel syndrome (IBS)—found that while basal cortisol levels were generally lower in FSDs, this association was not statistically significant overall. However, the review showed no significant cortisol reduction was observed in IBS.

So to bring this home, higher cortisol levels can increase risk for digestive problems and IBS symptoms. However, managing your stress on a regular basis can help with your symptoms, and help you enjoy some spikes in cortisol levels such as occasional high-intensity exercise, without long-term effects. While there is more to learn, this is promising! 

Some caveats for approaching high-intensity exercise… 

This said it’s always important to listen to your body and give it what it needs (if you listen, it will often tell you what it’s asking for!). While we’ve highlighted that high-intensity exercise can be something to enjoy with IBS when implemented with care, there are some instances when you may want to swap the session for something lower-intensity. This includes: 

During a period of high emotional stress: If your nervous system is already in fight or flight mode from an intense day at work, family emergency, or anything else that might lend itself to cortisol already being high, you might be best to swap the high-intensity workout you had planned for something a little more calming to the system like a yoga class or easy cycle. 

Mental Burnout: Burnout is considered a state of emotional, physical, and mental exhaustion that is typically caused by excessive and prolonged stress. If you are dealing with true burnout, stick to any form of exercise that feels good, while supporting your blood sugars and addressing the cause of your burnout. Though research is limited, there is some thought that high-intensity exercise may not be helpful in the early stages of burnout recovery but later on can be added back in when your body can handle it more effectively. 

You’ve under fueled: Gone all day running on coffee and a bite of a bagel? Your body will not perform nor handle high-intensity exercise optimally, so it’s best to get in some good fuel and leave that high-intensity workout for the next day (with a proper fuel strategy implemented!) Not to mention, we know that skipping meals and running on caffeine is a major trigger for IBS symptom flares too. Fuel your body & it will support you in return. 

Flare-Up Day Exercise Plan

Let’s say your IBS symptoms have reared their ugly head and a high-intensity session just isn’t in the cards for you today. That’s OK! Here are some workout ideas you can try instead: 

• Instead of a HIIT weight session, try a 15-minute bodyweight workout with long breaks between sets.
  • Do as many reps as you can in 30 seconds of the following exercises:
    • Push-ups
    • Air squats
    • Tricep dips (using a bench)
    • Standing lunges 
    • Plank hold 
  • Repeat 2 times
  • Take 30-60-second break between each repetition. 
• Go for an easy (3-4 RPE) run instead of a hard track session. 
• Try a yoga flow: consider an online class if you don’t feel like being in a public space. 
• Instead of a circuit workout, hop onto the elliptical or stationary rower for 25-30 minutes. 

While it may feel hard to get into, exercise can boost mood as well as low-moderate intensity movement can actually support digestive function so you will likely feel better once it’s done! 

More Support 

As always, reach out to a registered dietitian for support with fueling your exercise as well as managing IBS and gut health. Check out our Global Registered Dietitian Directory. 

Ready to fuel your workouts and sports performance, while keeping IBS and gut symptoms at bay with the right tools and strategies? My Pre & Post Workout Nutrition For a Happy Gut: Mini Course & Resource Bundle might be the next step for you! Use code FODMAPEVERYDAY for 15% off the usual price! 

The Takeaway 

You may be happy to know that high-intensity exercise CAN play a valuable role in your IBS and gut-friendly lifestyle. However, it must be approached with proper care and intention. While high-intensity exercise does temporarily cause a rise in cortisol levels, this is both a natural and beneficial response in the right doses. We can help mediate and optimize our cortisol response by managing our overall stress load, properly fueling our body for training sessions, and prioritizing rest and recovery. 

The key takeaways are to avoid fasted training before high-intensity sessions, ensure proper form and adequate rest during sessions, and include the right balance of training types and intensities throughout our week and training cycle. Further, high-intensity exercise should be included in an exercise program for those who already have a good aerobic and strength base, to prevent injury and ensure proper execution. 

If you’re unsure where to start or need personalized guidance to ensure you’re fueling properly, working with a Dietitian who specializes in sports nutrition and digestive health can help you tailor a plan that meets your unique needs. high-intensity exercise is not off the table for you if you have IBS, just make sure that it is incorporated into your regime properly and with the right planning for fuel, recovery, and stress management balance! 

References: 

1. https://www.cedars-sinai.org/blog/what-is-cortisol.html
2. https://www.healthdirect.gov.au/the-role-of-cortisol-in-the-body
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC8294064/
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC4826609/
5. https://pubmed.ncbi.nlm.nih.gov/29127602/

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