Do Protein Shakes Make You Poop?

📌 Overview and Key Takeaways

Why do protein shakes make you poop?

Discover what causes protein shake poops 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 Shake Poops

Why Do Protein Shakes Make You Poop?

If protein shakes make you run to the bathroom, you are not alone.

Protein supplements are notorious for causing digestive issues, including diarrhea.

Unless you have a food allergy or sensitivity, the reason why protein shakes make you poop has nothing to do with the type or amount of protein.

Instead, protein shakes make you poop because they contain added ingredients that are hard to break down and absorb.

Note that foods that are hard to digest cause diarrhea because their undigested components increase the osmotic load in your intestine.

This, in turn, draws water into your colon and accelerates colonic transit, which results in loose, watery stools.

Here are some of the top offenders:

🚫 Avoid Food Additives

Ultra-processed food additives like emulsifiers and thickeners tend to be hard to digest.

As a result, they can make you poop.

⚠️ 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 an ingredient in nature or make it at home, it is probably a food additive.

🚫 Avoid Dairy-Based Proteins

Dairy-based proteins like whey and casein are also hard to digest because they contain lactose, a sugar most adults cannot fully digest.

🚫 Avoid Artificial Sweetener and Sugar Alcohols

Artificial sweeteners and sugar alcohols resist digestion and can have a laxative effect (Eur J Clin Nutr, 2007).

Common artificial sweeteners include sucralose and acesulfame potassium.

Common sugar alcohols include erythritol and xylitol.

🚫 Avoid High Fiber

Insoluble fiber adds bulk to the stool, so if you eat a lot of it at once, it will make you poop.

High fiber protein supplement ingredients include inulin gums like xanthan gum and guar gum.

Believe it or not, many of these same ingredients are also used as laxatives (Br J Nutr, 1993)!

🚫 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 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 pre-existing digestive issues 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.

Keep in mind that what triggers diarrhea for one person, may not trigger it for someone else.

That said, it is safe to say that if your protein supplement makes you run to the bathroom, one (or more) of these ingredients is likely to blame.

It is also possible that preexisting gut issues are making you poop.

When you eat dietary protein, it enters the stomach where stomach acid and enzymes start to break it down into smaller components.

From there, the partially digested proteins move into the small intestine, where enzymes called proteases break them down into amino acids.

Amino acids are then absorbed through the intestinal lining and enter the bloodstream, which transports them throughout the body.

If any part of this complex process is not working properly due to preexisting gut issues, the protein you eat will not be fully broken down and absorbed.

Not only will this deprive you of the amino acids you need to stay strong and healthy, but it can also cause digestive issues.

Sources

1. European journal of clinical nutrition (Eur J Clin Nutr). Gastrointestinal tolerance of erythritol and xylitol ingested in a liquid. 2007.
2. The British journal of nutrition (Br J Nutr). The effect of feeding xanthan gum on colonic function in man: correlation with in vitro determinants of bacterial breakdown. 1993.
3. Nutrients (Nutrients). Effect of a Protein Supplement on the Gut Microbiota of Endurance Athletes: A Randomized, Controlled, Double-Blind Pilot Study. 2018.
4. 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.

Editorial Guidelines

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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.