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
May 13, 2026

Author and Medical Reviewer

Written by Jack, CNC

Jack is a National Academy of Sports Medicine Certified Nutrition Coach.

Disclaimer: This article is for general informational purposes only and is not a substitute for personalized medical advice. Consult a licensed healthcare professional before making changes to your diet.

Protein Shakes Make My Stomach Hurt

Why Do Protein Shakes Hurt My Stomach?

If you experience stomach pain after drinking protein shakes, you are not alone.

Many people find that drinking protein shakes causes bloating and stomach pain.

I myself have experienced digestive issues with protein supplements.

It was not until I started reading ingredient lists that the side effects made sense.

Protein shakes make your stomach hurt because they contain artificial and/or ultra-processed ingredients.

These ingredients tend to be hard to break down and absorb.

As you might imagine, this can lead to gastrointestinal (GI) symptoms, including stomach pain.

🚫 Avoid Food Additives

Emulsifiers, thickeners, and other ultra-processed additives look nothing like real food – and your gut knows it.

Because most additives are difficult to digest, they pass largely intact into your intestines, where your gut bacteria ferment them.

A byproduct of fermentation is gas, which can cause bloating, stomach pain, and even constipation.

Beyond day-to-day discomfort, regularly consuming certain additives can alter the composition and function of your gut microbiome — the community of living in your digestive tract (North Clin Istanb, 2020).

These shifts, known as gut dysbiosis, have been linked to chronic digestive conditions and persistent, painful symptoms (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 Dairy-Based Proteins

Dairy-based proteins like whey and casein, although not a problem for everyone, can cause digestive issues too.

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.

For starters, the digestion of some caseins releases a bioactive peptide that has been linked to digestive issues (Adv Nutr, 2017).

Casein also forms a gel-like substance in your stomach that slows down digestion (Crit Rev Food Sci Nutr, 2023).

For sensitive individuals, particularly true for those with cow’s milk protein allergy or intolerance, slower digestion can contribute to bloating, constipation, and other side effects.

🚫 Avoid Protein Concentrates and Isolates

If you have a sensitive stomach, you might also want to avoid 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 you break them down.

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

For example, one study shows that regularly consuming protein concentrates and isolates might disrupt your gut microbiome (Nutrients, 2018).

Another study shows that it could cause the formation of toxic byproducts in your gut (Mol Nutr Food Res, 2024).

Although further research is needed, individuals with sensitive stomachs can play it safe by choosing protein supplements made from minimally-processed protein sources like egg whites and almonds.

They are more gut-friendly.

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. Different brands use different ingredients. Trying another brand might solve your stomach problems.
2. Adjust the serving size. You might be drinking too much protein shake at once or drinking it too quickly, which can overwhelm your digestive system. Try drinking a smaller amount and sip it slowly to see if the stomach pain decreases.
3. Change the timing. Some people find that drinking protein shakes with meals, rather than on an empty stomach, reduces digestive issues. Try different times to see what works best for you.
4. Mix it with different ingredients. The ingredients you add to your protein shake can affect digestion. High-fiber fruits and vegetables, for example, can upset your stomach. Try different combinations or keep it simple 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 can cause stomach pain.

By listening to your body and following these steps, you will find a protein shake that meets your nutritional needs and agrees with your digestive system.

Remember that stomach pain can range from mild to severe and can 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.

Sources

1. Northern Clinics of Istanbul (North Clin Istanb). Food additives and microbiota. 2020.
2. JGH Open (JGH Open). Gut microbiota dysbiosis in functional gastrointestinal disorders: Underpinning the symptoms and pathophysiology. 2021.
3. Advances in Nutrition | Journal (Adv Nutr). Systematic Review of the Gastrointestinal Effects of A1 Compared with A2 β-Casein. 2017.
4. Critical Reviews in Food Science and Nutrition (Crit Rev Food Sci Nutr). Milk proteins: Processing, gastric coagulation, amino acid availability and muscle protein synthesis. 2023.
5. Nutrients (Nutrients). Effect of a Protein Supplement on the Gut Microbiota of Endurance Athletes: A Randomized, Controlled, Double-Blind Pilot Study. 2018.
6. 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 Certified Nutrition Coach and reviewed by a Registered Dietitian. We rely on peer-reviewed research and trusted medical sources, and regularly update our content to ensure accuracy and clarity.