Why Do Protein Shakes Make My Stomach Hurt?

📌 Overview and Key Takeaways

Why do protein shakes make my stomach hurt? Discover why protein shakes can upset your stomach and how to avoid this common side effect.

Last Updated
Jan 8, 2026

Author and Medical Reviewer

Written by Kayla Kamen, MS, RD

Kayla Kamen is a Registered Dietitian with a MS in Nutrition.

Medically reviewed by Jennifer Fossett, PA-C

Jennifer Fossett is a Physician Assistant with a BA in Nutritional Sciences.

Protein Shakes Make My Stomach Hurt

Why Do Protein Shakes Hurt My Stomach?

If you experience protein shake stomach aches, you are not alone.

Many people experience digestive issues like bloating and stomach pain after drinking protein shakes

I myself have a hard time digesting most protein supplements.

And it was not until I started reading ingredient lists that my side effects started to make sense.

Most protein shakes are made from artificial and/or ultra-processed ingredients.

This makes them hard to break down and absorb, which can lead to a range of gastrointestinal (GI) symptoms, including stomach pain.

Here are some of the top offenders:

🚫 Avoid Food Additives

Emulsifiers, thickeners, and other ultra-processed additives look nothing like real food, which makes them hard to digest.

As a result, they feed your gut bacteria, which release gas as they eat.

And too much intestinal gas can cause bloating, stomach pain, and even constipation!

Regularly eating certain food additives can also alter the composition and function of your gut microbiome (North Clin Istanb, 2019).

These shifts, known as gut dysbiosis, have been linked to a number of chronic digestive issues known to cause painful side effects (JGH Open, 2021).

⚠️ Here is a list of the most common food additives in protein supplements:

• acacia fiber
• acacia gum
• acesulfame potassium
• artificial flavors
• ascorbic acid
• aspartame
• calcium carbonate
• carrageenan
• cellulose gum
• dextrin
• dicalcium phosphate
• dipotassium phosphate
• erythritol
• gellan gum
• guar gum
• gum arabic
• inulin
• locust bean gum
• maltitol
• maltodextrin
• mono- and diglycerides
• ‘natural’ flavors
• rice bran extract
• rice dextrin
• rice hulls
• rosemary extract
• silica
• silicon dioxide
• sodium alginate
• soluble corn fiber
• sorbitol
• soy lecithin
• sucralose
• sunflower lecithin
• tocopherols
• tricalcium phosphate
• xanthan gum
• xylitol
• zinc oxide

As a rule of thumb, if you cannot find it in nature or make it at home, it is probably a food additive.

🚫 Avoid Added Vitamins and Minerals

Added vitamins and minerals in protein supplements might cause digestive issues too.

Certain micronutrients can affect gut barrier function and immune response, indirectly influencing gastrointestinal health.

In one case, the chronic overconsumption of vitamins (A, selenium, zinc) led to permanent stomach pain (J Int Soc Sports Nutr, 2015).

🚫 Avoid Dairy-Based Proteins

Dairy-based proteins like whey and casein, although not an issue for everyone, can cause digestive issues.

This is usually because they contain lactose, a sugar many individuals with sensitive stomachs cannot fully digest.

But you might be sensitive to dairy-based proteins even if you are not lactose intolerant.

This is particularly true for casein protein, which forms a gel-like substance in your stomach that slows down digestion.

🚫 Avoid Protein Concentrates and Isolates

If you have a sensitive stomach, you might also want to avoid ultra-processed protein concentrates and isolates.

Most protein supplements are made from one or both of these ultra-processed protein sources, which have been mechanically and/or chemically stripped of everything but the protein.

This includes the enzymes, fiber, and other natural digestive aids that help your gut break them down.

You therefore do not digest them in the same way that you do whole foods, which could affect your gut health.

Studies show that regularly eating protein concentrates and isolates might disrupt your gut microbiome (Nutrients, 2018) and cause the formation of toxic byproducts in your gut (Mol Nutr Food Res, 2024).

Individuals with sensitive stomachs should thus look for protein supplements made from whole food protein sources like egg whites and almonds, which are easier to digest and absorb.

Order Samples to see for yourself.

What Should I Do if Protein Shakes Hurt My Stomach?

If protein shakes upset your stomach, try the following:

1. Switch brands: Not all protein shakes are created equal. Different brands use different ingredients, so trying a different brand might solve the problem.
2. Adjust the serving size: It is possible that you are consuming too much protein shake at once, or drinking your shake too fast, which can overwhelm your digestive system. Try reducing the serving size and sipping slowly to see if that helps reduce the stomach pain.
3. Change the timing: Some people find that consuming protein shake before or after a meal, rather than on an empty stomach, reduces digestive issues. Experiment with different timing to see what works best for you.
4. Mix it with different ingredients: The ingredients put in your protein shake can affect digestion. High fiber fruits and veggies, for example, can upset your stomach. Try changing it up or sticking to the basics to see if that helps.
5. Try a different liquid: If you are using cow’s milk, try plant milk or water. Cow’s milk contains lactose, which is notorious for causing stomach pain.

By listening to your body and following the steps above, you will find a protein shake that not only meets your nutritional needs, but also agrees with your digestive system.

Keep in mind that stomach pain can range from mild to severe, and last for a few minutes to a few hours.

Call your doctor if you have pain so severe that you cannot move without causing more pain, or if you cannot find a comfortable position.

Sources

1. Northern Clinics of Istanbul (North Clin Istanb). Food additives and microbiota. 2019.
2. JGH Open: An Open Access Journal of Gastroenterology and Hepatology (JGH Open). Gut microbiota dysbiosis in functional gastrointestinal disorders: Underpinning the symptoms and pathophysiology. 2021.
3. Journal of the International Society of Sports Nutrition (J Int Soc Sports Nutr). The risks of self-made diets: the case of an amateur bodybuilder. 2015.
4. Nutrients (Nutrients). Effect of a Protein Supplement on the Gut Microbiota of Endurance Athletes: A Randomized, Controlled, Double-Blind Pilot Study. 2018.
5. Molecular nutrition & food research (Mol Nutr Food Res). In Vitro Fermentation of Animal and Plant Protein Isolates by the Human Gut Microbiota Under High and Low Carbohydrate Conditions. 2024.

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This article was written by a Registered Dietitian and reviewed by a Physician Assistant. We rely on peer-reviewed research and trusted medical sources, and regularly update our content to ensure accuracy and clarity.