Why Does Oat Milk Hurt My Stomach? (How to Prevent It)

Written by: Jeana Marie

For some people, drinking plant-based milk like oat milk offers relief from digestive discomfort caused by cow’s milk.  

However, you may experience stomach pain or intestinal discomfort after drinking oat milk even though it doesn’t contain the same ingredients, such as lactose, that normally cause issues with dairy milk. 

You might have stomach discomfort and digestive problems after drinking oat milk because you have an allergy to oats or gluten, an intolerance to high-fiber foods, or issues with food additives found in store-bought oat milk.

Learn more about why oat milk is causing your stomach pain and the steps you can take to address this troublesome issue. 

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How To Avoid Stomach Pain When Drinking Oat Milk

Here are our suggestions to help if you’re experiencing oat milk stomach aches: 

Get a Food Sensitivity or Allergen Test

If you’ve tried multiple oat milk brands, and they all give you a stomach ache, there’s a chance you might have an oat allergy. The quickest way to find out is with a food allergen test.

Getting tested is extremely easy these days.

You can order an at-home food sensitivity test online. We recommend Everylywell.

Try A Different Oat Milk 

When it comes to oat milk, our general rule of thumb is the fewer ingredients it contains, the better.

A lot of popular oat milk brands are loaded with additives and preservatives that can wreak havoc on your gut.

Look at the ingredient list on the back of your oat milk. If it contains ingredients like gellan gum, rapeseed oil, and phosphates, that could be the reason you’re experiencing gas and an upset stomach after drinking it.

We review and test hundreds of milk brands, and we’ve found the ones with simpler ingredients give us the least gut issues.

One brand we love and recommend is Willa’s.

Their unsweetened original version contains all natural and organic ingredients, and we’ve found it’s comparable to big-name brands.

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If one brand or even flavor of oat milk upsets your system, try different oat milk to see if it suits your body better.

Additionally, you can make your own oat milk to have more control over what you put into the blend. 

Fix Your Gut

If you have digestive issues in general, it could be a sign of problems with your overall gut health. Unfortunately, gut health issues are extremely common due to how food has changed over time (more preservatives, additives, sugar, etc.)

The good thing is there are simple steps you can take to improve your gut health. One of the first things I’d suggest is getting a probiotic.

Probiotics contain healthy bacteria that can balance out the microorganisms in your gut. While the jury is still out about their overall efficacy, I’ve personally noticed good results with them. 

And according to the National Institutes of Health (NIH), probiotics have shown promise for preventing diarrhea and symptoms of ulcerative colitis.

I’d recommend giving them a try and if you notice a difference after drinking oat milk. Here’s a brand we recommend.

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Check For Spoilage

If you drink oat milk and feel ill afterward, check the beverage for spoilage.

Look for holes in the carton, bloated or leaking packaging, or off smells coming from the liquid.

If you see any mold growth or notice curdling, throw out the container.

Monitor your symptoms and if you experience severe food poisoning, seek medical attention. 

Try An Alternative Plant-Based Milk

If oat milk bothers your digestive system, choose different plant-based milk. You can try beverages such as:

Why Oat Milk Can Cause Digestive Problems

Most of the stomach problems caused by drinking oat milk are due to the following issues: 

Oat Allergies

Although rare, some people are allergic to avenin, a protein found in oats.

You will likely experience an allergic reaction after drinking oat milk if you have this allergy.

Depending on the severity of your allergy, you may exhibit any of the following symptoms starting from a few hours after consumption to several days safer drinking the beverage:  

  • Red, flushed face
  • Hives or eczema
  • Reflux 
  • Sneezing
  • Runny eyes and nose
  • Itchy mouth and throat
  • Swelling in the face, mouth, or neck
  • Stomach cramps, bloating, nausea, vomiting, constipation, or diarrhea

You may experience anaphylactic shock after consuming oat milk if you have a severe oat allergy. 

man holding stomach and raising hand drinking expired spoiled milk

Sensitivity or Allergy to Gluten

If you have a sensitivity or allergy to gluten, oat milk can upset your stomach and intestines. 

People with Celiac Disease often have issues with oats and oat milk even though oats themselves are gluten-free.

Oat is often processed in the same factories as other products, so cross-contamination is common.

If you are sensitive to gluten, opt for an oat milk brand that states “gluten-free” on its packaging.

Check out the article below to see the best gluten-free oat milk brands.

Issues With Additives

Oat milk on its own isn’t great for avoiding acid reflux, and oat milk with additives and extra sugar is even worse.

Common additives in oat milk can include the following:

  • Xanthan gum
  • Potassium sorbate
  • Sodium benzoate
  • Disodium phosphate
  • Carrageenan
  • Sunflower oil
  • Safflower oil
  • Sunflower lecithin
  • Sugar
  • Gellan gum
  • Chicory root
  • Other natural flavors

These additives can cause a reaction in people with sensitive digestive systems.

If you feel stomach discomfort after drinking oat milk, look at the ingredient list to see if there’s an additive that’s made you feel “off” in the past. 

Intolerance of High-Fiber Foods

While fiber is generally recognized as a digestive aid because it moves food through the large intestine, too much fiber can have the opposite effect.

If you already eat a lot of fiber in your diet, drinking oat milk can add to your cumulative daily amount.

Those with fiber sensitivity might feel bloated, constipated, and uncomfortable after drinking oat milk. 

Preexisting Digestive Condition

Anyone with a digestive contusion like Chrone’s Disease, Irritable Bowel Syndrome, SIBO, or Inflammatory Bowel Disease may experience an upset stomach after drinking oat milk.

These conditions require constant monitoring of your food intake and various ingredients, especially oat milk additives, can set off your symptoms.

While oat milk is often considered a good choice for people with these conditions, you have to pay attention to your body’s symptoms to learn if you can tolerate it. 


Like all other foods, oat milk can go bad if not stored correctly.

Like almond milk, opened oat milk should be stored in the refrigerator at below 40℉ and consumed within 7-10 days after opening.

If you leave oat milk out at room temperature after it’s been opened, it will start growing microscopic bacteria and mold within two hours.

If you drink contaminated oat milk, you’ll likely experience symptoms of food poisoning such as stomach pains, nausea, vomiting, or diarrhea. 

man holding stomach drinking expired spoiled milk

Possible Stomach Issues Caused By Oat Milk

Oat milk can cause many different stomach issues.

These can result from problems with added ingredients or the oats themselves.

Possible problems you might experience after drinking oat milk include the following:  


Your stomach pain after drinking oat milk can feel like excess gas in your system.

Gas pain can feel like knots in your stomach and intestines or a feeling of fullness.

It can also cause bloating, which causes your stomach to feel pressure and appear full and large.

You may burp a lot when you have gas after drinking oat milk, and if the gas stays trapped in your system, it can feel extremely painful.  


Stomach pain can also be caused by diarrhea after drinking oat milk.

Diarrhea causes loose, watery stool. It can happen due to a change in your diet or bacterial infection after drinking spoiled oat milk.

Diarrhea is often your body’s way of telling you that something in the oat milk doesn’t agree with your system.

It’s a good idea to avoid drinking more oat milk until you understand the source of the issue.  

Acid Reflux

Some stomach pain can be caused by acid reflux.

Acid reflux is a condition that causes stomach acid to rise into your esophagus, causing a burning, painful sensation.

Although oat milk has a neutral pH (about 6.7 to 6.9), if you have a sensitive system, you might experience heartburn due to one of the additives in store-bought oat milk. 


Nausea is a feeling that you may experience after drinking oat milk.  

Nausea may be accompanied by vomiting, stomach cramps, or diarrhea.

Nausea can occur for many reasons after drinking oat milk. You may feel nauseous after drinking spoiled or curdled oat milk or if your body disagrees with one of the additives in the brand you purchased.

Nausea after drinking oat milk is typically short-lived and will usually go away after a few hours. 


Constipation is the uncomfortable inability to pass stool through your digestive system.

Constipation can cause cramping, bloating, a feeling of fullness, and general digestive upset.

You might experience constipation after drinking oat milk if you ingest multiple servings and your bowels react poorly to added sugar or too much fiber. 

man holding stomach with left hand drinking expired spoiled milk

What Ingredients Are In Oat Milk?

Oat milk is a plant-based beverage made from whole oats. To make oat milk, manufacturers soak whole oats in water. 

Then, they rinse the oats and blend them with filtered water.

This mixture is typically strained to remove any large pieces of oats to achieve a final creamy texture. 

Most store-bought oat milk contains additional ingredients.

These can include simple ingredients like salt and cane sugar.

Fortified oat milk may contain added vitamins like Vitamin A, Vitamin D, and calcium. 

These brands also often contain emulsifiers and oils to enhance the beverage's taste and texture.

Sunflower oil, carrageenan, disodium phosphate, guar gum, and gellan gum are all common additives in oat milk, depending on the brand. 

Bottom Line About Stomach Discomfort and Oat Milk

Like any food, oat milk can cause stomach pain or digestive discomfort if you have a preexisting condition or sensitivity to its ingredients. 

If you notice stomach pain or digestive problems after drinking oat milk, take note of how you are feeling, how quickly after drinking your symptoms occurred, and what type of oat milk you ingested.  

Then, work to narrow down the cause by checking the oat milk for spoilage or assessing whether you may have an allergy or sensitivity to an ingredient. 

Once you know the reason the oat milk is causing discomfort, you can take action to remedy the situation and enjoy the right oat milk or choose another plant-based beverage.

About the Author

Jeana Marie is a freelance digital content writer. Her writing focuses on mental health, self-improvement, and healthy living. When she's not writing, Jeana enjoys spending time with her daughters and discovering new coffee and herbal tea flavors.