Why Does Pre-Workout Make You Poop? (Expert's Opinion) 

Benedict Ang, CPT, PN1-NC
Published by Benedict Ang, CPT, PN1-NC | Staff Writer & Senior Coach
Last updated: April 1, 2024
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Why pre-workouts make you poop is a common question I get from my clients who use these supplements to boost their workouts.

While abnormal bowel movements are not something I've encountered with pre-workouts, I decided to check with a nutritionist about why some people might end up with some stomach issues.

It turns out that there are some common pre-workout ingredients that occasionally cause stomach issues. So, we did some deeper research for a few weeks to see if we could figure out what causes it and whether there are ways to avoid it.

So, why does pre-workout make you poop? Let's take a look.

Quick Summary

  • Pre-workout supplements can make you poop because of the combination of the ingredients, and also depending on how you are using it.
  • The ingredients that might affect your stomach are caffeine, artificial sweeteners, magnesium, and lactose.
  • According to the Journal of the International Society of Sports Nutrition, caffeine, a common pre-workout ingredient, not only improves strength and delays muscle fatigue but is also linked to increased bowel movements.
  • I believe that the key to a good pre-workout is not just about the lift it gives but also how gently it sits in your stomach.

Why Does Pre-Workout Make Me Poop?

A woman sitting on the toilet

If your pre-workout supplement sends you to the bathroom often, it's likely due to its ingredients and how you're using it. Your body's natural reaction to exercise also plays a role, as it can stir up your gut microbiome and digestion.

In my and my clients' experience, it's usually down to caffeine or artificial sweeteners.

The Journal of the International Society of Sports Nutrition acknowledges caffeine as a key pre-workout component for boosting strength and staving off muscle fatigue [1].

Meanwhile, sources like the McGill Office of Science and Society link caffeine to more frequent bowel movements [2].

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From my fitness training experience, I've noticed the real issue often lies in the super high doses of stimulants in some supplements. Downing a hefty dose of caffeine, especially if you've already had coffee, can really upset your stomach.

As per reports in the National Library of Medicine, the other ingredient that can cause stomach issues and even diarrhea is some form of artificial sweetener [3]. The other thing that can contribute to bowel trouble is how much and when you take your pre-workout.

Pre-Workout Ingredients That Might Affect Your Stomach

A man holding a toilet paper roll while sitting on the toilet

I gathered the names of each pre-workout supplement that my clients had reported issues with and then had my nutritionist review them to see what the most likely cause was.

Caffeine

As per reports in the Journal of Strength and Conditioning Research, most pre-workout supplements contain some amount of caffeine, and that is because it can help you achieve a more intense workout session [4].

As we’ve mentioned, caffeine has been linked to increased bowel movements, but the main reason this might cause issues more often than it actually should is a high dose of these supplements, which can even lead to diarrhea, as per reports on Healthy Women [5].

The products that I recommend generally have less than 200 mg of caffeine, and that's about the same as two cups of coffee. While the Mayo Clinic says 400 mg per day is safe, you don't want to get that all in one go [6].

In the end, if you are sensitive to it, caffeine-free pre-workouts are the best option for you.

Artificial Sweeteners

Sugar spilled in a table

Artificial sweeteners are common in all supplements, not just pre-workouts. Havard Medical School studies have shown that they can destabilize your gut flora, leading to many different bowel issues [7].

I've had clients complain about gut issues until we tweaked their supplement intake to those without sweeteners and it worked in most cases.

What happens is that undigested sweetener absorbs water, which leads to softer stool.

One problem, in particular, is diarrhea, and it's often linked to a regular and consistent intake of artificial sweeteners.

You need to watch out for this when you take pre-workout supplements four or five times a week.

Lactose

Lactose is less common in these products, but one of my clients used a pre-workout supplement that had lactose, and it was causing him many stomach issues.

According to Mayo Clinic, if you have any kind of lactose intolerance, then it can make you poop a lot more often at very inconvenient times [8].

Magnesium

According to research published by the National Institutes of Health, Magnesium is an important mineral for muscle mass and a healthy lifestyle in general [9].

However, some forms of this mineral can trigger digestive discomfort in the form of cramps, bloating, and diarrhea, as per reports by the Mayo Clinic.

If you see a high dose of magnesium in a pre-workout and you take it in some other form as well, then you could end up with stomach issues.

"​​Magnesium supplements can cause nausea, cramps, and diarrhea. Magnesium supplements often cause softening of stool."

- R. Morgan Griffin, Writer & Editor at WebMD.com

Other Contributing Factors

A man having stomach pain

Beyond the ingredients in your chosen pre-workout supplements, there are a couple of other things that can impact a timely bowel movement.

Timing

  • Caffeine Overload: Mixing a caffeine-rich pre-workout with your regular coffee can lead to a caffeine overload.
  • Meal Timing: Taking pre-workouts close to meal times can mess with your digestive enzymes, leading to more bathroom trips.
  • Supplement Stacking: Using multiple supplements with similar ingredients at the same time can also upset your stomach. Try skipping that coffee and staggering supplement intake to see if it helps.

Related Article: Pre-Workout vs Coffee

Dosage

Always read the labels for caffeine content. High doses, especially combined with coffee, can affect not just your bowels but also your brain, nervous system, and blood pressure, as noted in studies from the National Library of Science [11].

Empty Stomach

Taking pre-workouts on an empty stomach, especially before fasted cardio, can increase the likelihood of abnormal bowel movements, especially if they contain artificial sweeteners and magnesium.

Stress

Don't overlook the psychological angle. Stress can worsen gastrointestinal issues, and the intensity of workouts combined with pre-workout supplements might amplify this.

Tips For Reducing Pre-Workout Poops

A man holding a scoop of pre workout powder

We have created a list of the best men's pre-workouts after testing and researching dozens over the years. These have given us great results during training sessions, and they haven't caused any significant bowel problems so far.

If pre-workout has you running to the bathroom more than usual, here's what to do:

  • Change Your Pre-Workout - First up, check your pre-workout's label. If it's packed with caffeine and reads like a science experiment, it might be messing with your gut. We've tried plenty and found several low or no caffeine pre-workouts that keep your energy up without the bathroom sprints.
  • Cut Back on Coffee - Love your caffeine-laden pre-workout? Then consider dialing back your coffee intake. Trust me, I've been there – needing to avoid stomach troubles before a workout.
  • Check Overlapping Ingredients - Mixing supplements? Be careful. If you're popping a fat burner and downing mineral supplements, you might overdo it on something like magnesium. If your supplements share a lot of ingredients, stagger their timing to avoid taking them too close together. This can help dodge those unwanted bathroom breaks.

FAQs

Does Pre-workout Make Your Stomach Hurt?

Yes, some pre-workout products can make your stomach hurt. But there are supplements that have a more stomach-friendly formula to help you avoid cramps and bloating.

How Do You Stop Pre-workout Diarrhea?

You can stop pre-workout diarrhea by making sure you don't take a product with too much caffeine and artificial sweeteners. You should also try to take it with some food to avoid stomach upset.


References:

  1. https://jissn.biomedcentral.com/articles/10.1186/s12970-020-00383-4
  2. https://www.mcgill.ca/oss/article/health-nutrition/why-does-coffee-make-you-poop
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6363527/
  4. https://journals.lww.com/nsca-jscr/Fulltext/2016/10000/Effect_of_Coffee_and_Caffeine_Ingestion_on.27.aspx
  5. https://www.healthywomen.org/content/article/signs-youre-consuming-too-much-caffeine
  6. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/caffeine/art-20049372
  7. https://www.health.harvard.edu/diseases-and-conditions/is-something-in-your-diet-causing-diarrhea
  8. https://www.mayoclinic.org/diseases-conditions/lactose-intolerance/symptoms-causes/syc-20374232
  9. https://pubmed.ncbi.nlm.nih.gov/26288012/
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About The Author

Benedict Ang, CPT, PN1-NC
Staff Writer & Senior Coach
Benedict Ang, CPT, PN1-NC is an ex-National Soccer player turned MMA and Kickboxing champion, with ACE CPT and PN1-NC certifications. His advice is rooted in education and experience, ensuring that readers receive scientific and battle-tested insights. His mission is to empower his clients and readers to realize their potential and become the best versions of themselves.
Learn more about our editorial policy
Dr. Harshi Dhingra, MBBS, MD is a published peer-reviewed author and renowned physician from India with over a decade of experience. With her MBBS from Bharati Vidyapeeth and an MD from Rajiv Gandhi University, she actively ensures the accuracy of online dietary supplement and medical information by reviewing and fact-checking health publications.
Learn more about our editorial policy
Dr. Kristy June Dayanan, BS, MD is an author with a BS degree from University of the Philippines and an MD from University of Perpetual Help System. Her ability to simplify medical science complexities and dietary supplement jargon for the average reader makes her a valued medical fact checker and reviewer.
Learn more about our editorial policy

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