Can Meal Replacement Shakes Cause Diarrhea?

📌 Overview and Key Takeaways

Can meal replacement shakes cause diarrhea?

Discover what causes meal replacement shake diarrhea and how to avoid this common side effect.

Last Updated
Jul 21, 2026

Author and Medical Reviewer

Jack, CNC

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

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Disclaimer: This communication is for general informational purposes only and is not a substitute for personalized medical advice.

Meal Replacement Shake Diarrhea

Do Meal Replacements Cause Loose Stools?

Meal replacement shakes are designed to be a convenient way to replace the nutritional value of a meal.

In other words, they are a quick and easy way to incorporate calories, protein, and other nutrients into your diet.

Despite their benefits, however, meal replacement shakes can cause a number of unpleasant digestive issues, including diarrhea.

How Do I Avoid Meal Replacement Shake Diarrhea?

Meal replacement diarrhea is easy to avoid if you are mindful of two factors: pre-existing digestive issues and ingredients.

Preexisting digestive issues can make you more likely to experience diarrhea.

When you eat, food makes its way to your stomach where stomach acid starts to break it down into smaller components.

From there, it moves to your small intestine, where enzymes break it down into small amino acids, sugars, fatty acids, etc.

Most of these smaller components are then absorbed through your 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 food you eat will not be fully broken down and absorbed.

This can lead to diarrhea because partially-digested food has an osmotic effect, drawing water into the colon.

So, if you think that pre-existing gut issues might be contributing to your diarrhea, consult a healthcare practitioner for a professional diagnosis.

That said, anyone can experience diarrhea if they are not careful about what they eat.

This is because some ingredients, especially artificial and ultra-processed ones, are hard to digest, even for healthy guts.

Here are some of the top meal replacement ingredients to avoid if sick and tired of running to the bathroom:

🚫 Avoid Food Additives

Emulsifiers, thickeners, and other ultra-processed additives tend to resist digestion, which can lead to diarrhea.

⚠️ Here is a list of the most common food additives in meal replacements:

• 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

Regularly eating certain food additives can also alter the composition of your gut microbiome – the collection of microorganisms living in your gut (North Clin Istanb, 2019).

These shifts, known as gut dysbiosis, have been linked to the development of chronic digestive issues, including diarrhea (Front Microbiol, 2025).

As a rule of thumb, if you cannot find it in nature, or make it in your home kitchen, 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 example, the digestion of some caseins releases a bioactive peptide that has been linked to digestive issues (Adv Nutr, 2017).

Avoid Artificial Sweeteners and Sugar Alcohols

Many artificial sweeteners and sugar alcohols have a laxative effect.

Common artificial sweeteners include sucralose and acesulfame potassium.

Common sugar alcohols include erythritol, sorbitol, and xylitol.

Avoid Insoluble Fiber

Some meal replacements, especially those intended to help with weight loss, contain added insoluble fiber.

Insoluble fiber adds bulk to the stool, so if you eat a lot of it at once, it can cause diarrhea.

Some high fiber ingredients to look out for are guar gum and inulin.

🚫 Avoid Protein Concentrates and Isolates

You might also want to avoid protein concentrates and isolates.

Most meal replacements contain one or both of these ultra-processed protein sources, which have been mechanically and 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 meal replacements 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 I Have Meal Replacement Diarrhea?

If you have diarrhea after drinking a meal replacement shake, take the following steps:

• Stay hydrated. Diarrhea can lead to dehydration due to fluid loss. Drink plenty of clear fluids and avoid caffeinated and alcoholic beverages.
• Eat bland foods. Stick to bland, easily digestible foods such as bananas and rice. These foods can help firm up stools without aggravating your stomach.
• Rest. Give your body time to recover by getting plenty of rest. Avoid strenuous activities that can further deplete your energy levels.
• Seek medical attention. If your diarrhea persists for more than a couple of days, you should consult a healthcare professional. They can help determine the underlying cause and provide appropriate treatment.

Keep in mind that in most cases, diarrhea only lasts 24-48 hours; if it lasts longer, consult a medical professional.

Sources

1. Northern Clinics of Istanbul (North Clin Istanb). Food additives and microbiota. 2019.
2. Frontiers in Microbiology (Front Microbiol). The role of gut microbiota in diarrhea and its alleviation through microbiota-targeted interventions. 2025.
3. Advances in Nutrition | Journal (Adv Nutr). Systematic Review of the Gastrointestinal Effects of A1 Compared with A2 β-Casein. 2017.
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.

Editorial Guidelines

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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.