What is in protein powder that makes my stomach hurt?

January 6, 2026 •

3 min read

Research indicates that approximately 65% of the world's population has a reduced ability to digest lactose after infancy, a common culprit for digestive discomfort from milk-based protein powders. Beyond lactose, other ingredients and consumption habits can be responsible for an upset stomach after drinking a protein shake.

Quick Summary

Several ingredients in protein powders, such as lactose in whey, artificial sweeteners, and certain additives like thickeners and fibers, can cause stomach pain. The type of protein and how it is consumed also impacts digestive comfort. Strategies like switching protein types or adjusting consumption habits can resolve discomfort.

Key Points

Lactose Intolerance: Many people with undiagnosed lactose intolerance experience digestive issues with whey concentrate protein due to its lactose content.
Artificial Sweeteners: Sugar alcohols like erythritol and sweeteners like sucralose can ferment in the gut, causing gas, bloating, and discomfort.
Thickeners and Gums: Additives such as xanthan gum and inulin, used for texture, are difficult for some individuals to digest and can lead to bloating.
Consumption Habits: Drinking protein shakes too quickly or consuming large amounts after an intense workout can overwhelm the digestive system.
Protein Source Matters: Switching from dairy-based whey to a plant-based or hydrolyzed protein can often resolve stomach issues for sensitive individuals.

Common Culprits in Protein Powders

If your protein powder consistently leaves you with an upset stomach, the cause is likely a specific ingredient or a combination of factors related to how your body processes it. While the protein source itself is a major factor, artificial additives and consumption habits play a significant role.

Lactose in Whey Protein

Lactose, the sugar in milk, is a frequent cause of digestive distress from whey protein, which is derived from milk. The amount of lactose varies depending on the type of whey. Individuals with lactose intolerance lack enough lactase, the enzyme needed to break down lactose, leading to gas, bloating, cramps, and diarrhea.

Whey Protein Concentrate (WPC): Has higher lactose and is more likely to cause symptoms.
Whey Protein Isolate (WPI): Most fat and lactose are removed, making it better for mild sensitivity.
Whey Protein Hydrolysate (WPH): Pre-digested protein that is easier to digest.

Artificial Sweeteners and Sugar Alcohols

Artificial sweeteners like sucralose and sugar alcohols such as sorbitol and erythritol are used in many flavored protein powders. Since they aren't fully absorbed, they ferment in the large intestine, causing gas, bloating, and discomfort. A 2022 trial linked non-caloric sweeteners to increased reports of diarrhea and abdominal discomfort. Opting for unflavored or naturally sweetened powders may help.

Additives and Thickeners

Thickeners and gums like xanthan gum, guar gum, and inulin are added for texture but can be hard to digest for some, leading to gas and bloating. High amounts of added fiber, especially inulin, can cause problems if not accustomed to it. Carrageenan, a seaweed-based thickener, has also been associated with GI issues.

Protein Type and Quality

The protein source and processing are important. Plant-based proteins may be easier for those with dairy sensitivity, but even pea protein can be an issue for those sensitive to FODMAPs. Soy protein contains gas-producing oligosaccharides. Fillers and low-quality ingredients can also affect digestion.

Consumption Habits

How you drink your shake matters. Intense exercise can slow digestion, so wait about 30 minutes before drinking. Drinking too fast can cause you to swallow air, leading to bloating. Large doses of protein at once can be hard to digest, so stick to recommended servings. Not drinking enough water can also contribute to constipation.

Whey vs. Plant-Based Protein for Digestive Comfort


Feature	Whey Protein	Plant-Based Protein	Best for Sensitive Stomachs?
Source	Cow's milk, a dairy product.	Various plant sources (pea, rice, hemp).	Plant-Based, generally lactose-free.
Digestibility	Fast-absorbing, but can be difficult for those with lactose intolerance.	Often gentler on the digestive system due to lack of dairy.	Plant-Based is often gentler, with hydrolyzed whey also an option.
Lactose Content	Contains lactose (less in isolate/hydrolysate, more in concentrate).	Naturally lactose-free.	Plant-Based (or whey isolate/hydrolysate).
Common Additives	May include artificial sweeteners, gums, and flavors.	May contain thickeners, digestive enzymes, or sweeteners.	Plant-based powders with minimal, natural ingredients.
Fiber Content	Generally very low in fiber.	Often contains natural dietary fiber, aiding digestion.	Plant-based for added fiber benefits.

How to Reduce Digestive Distress

Consider a different protein source. Try a low-lactose whey isolate, hydrolyzed protein, or plant-based option like pea or rice protein.
Read the ingredient list carefully. Avoid artificial sweeteners and thickeners like xanthan gum. Choose products with minimal, natural ingredients.
Check your serving size. Stick to recommended amounts (typically 25-35 grams) to avoid overwhelming your digestive system.
Drink it slowly. Sipping prevents swallowing air and reduces bloating.
Wait after your workout. Allow about 30 minutes for your digestive system to settle before consuming your shake.
Stay hydrated. Adequate water intake aids digestion and absorption.
Try a protein with digestive enzymes. Look for powders with added enzymes like lactase or consider a separate supplement.

Conclusion

Identifying what is in protein powder that makes your stomach hurt is key to finding a suitable supplement. Causes often include lactose, artificial sweeteners, or additives. By understanding these ingredients, exploring alternative protein types, and adjusting how you consume your shake, you can reduce digestive side effects. Consulting a healthcare professional can offer personalized advice. Healthline provides a guide to protein powders for sensitive stomachs.

Frequently Asked Questions

Whey protein can cause stomach cramps and bloating, particularly whey concentrate, because it contains lactose. Many people are lactose intolerant and lack the enzyme lactase needed to break down this milk sugar, leading to fermentation and digestive discomfort.

Plant-based protein powders (pea, rice, hemp), whey protein isolate (WPI), or hydrolyzed protein are often the best choices for sensitive stomachs. They are either naturally lactose-free or have undergone processing to reduce lactose content, making them easier to digest.

Yes, artificial sweeteners and sugar alcohols (e.g., sorbitol, erythritol) in protein powders are known to cause digestive issues like bloating, gas, and stomach upset. Your gut bacteria can ferment these compounds, creating gas.

Yes, drinking a protein shake too quickly can overwhelm your digestive system and cause you to swallow excess air, both of which can lead to bloating and abdominal pain.

For many, taking protein powder with food can aid digestion and prevent discomfort. However, others find it easier to digest on its own. Experimenting with timing and consumption methods can help determine what works best for your body.

Yes, many protein powders avoid common thickeners like xanthan gum and guar gum. If you have a sensitive stomach, look for brands with minimal ingredients or those that use alternative thickeners that you tolerate well.

Hydrolyzed protein is a 'pre-digested' protein where the molecules have been broken down into smaller peptides. This process makes it easier for the body to absorb and utilize, significantly reducing the likelihood of digestive discomfort.