What Are the Side Effects of Meal Replacement Shakes?

📌 Overview and Key Takeaways

What are the side effects of meal replacement shakes?

Learn about the meal replacement ingredients most likely to cause side effects.

Last Updated
Jul 21, 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.

Meal Replacement Shake Side Effects

Do Meal Replacement Shakes Cause Side Effects?

Meal replacement side effects, also known as adverse reactions, are unwanted symptoms caused by the consumption of meal replacement shakes.

Common examples include acne, headaches, and digestive distress.

The last one is really common, that is, roughly 1 in 5 people experience bloating, constipation, diarrhea, gas, nausea, and/or stomach pain after drinking meal replacement shakes.

Keep in mind that severity and duration of side effects varies from person to person.

Why Do Meal Replacements Cause Adverse Reactions?

If a meal replacement causes side effects, the reason why can usually be found on the ingredient list.

Here are some of the most common side effects and problematic ingredients to avoid:

Acne

Meal replacements made with whey and/or casein are notorious for making people break out.

Dairy-based proteins can stimulate the production of insulin and insulin-like growth factor, both of which have been linked to acne development.

Although this link is not fully understood, it likely has something to do with the fact that insulin production regulates sebum production.

Sebum, an oily, waxy substance produced by your body’s sebaceous glands, can clog your pores and cause pimples.

Headaches

Meal replacement shakes are known to cause headaches or even migraines.

Here are some of the ingredients that may be the problem:

• Caffeine: Caffeine is a common headache trigger, so if you are sensitive to caffeine, you may want to avoid chocolate, coffee, and matcha-flavored protein powders.
• Sugar: Some protein powders contain lots of added sugar, which can cause spikes and crashes in blood glucose levels, leading to headaches.
• Dairy: Protein shakes or powders made with whey or casein, can trigger a histamine response in certain individuals. This can lead to headaches, particularly in those who are histamine intolerant.
• Artificial sweeteners: For some people, the culprit may be artificial sweeteners. Although it is hard to say that there is a definitive connection between headaches and artificial sweetener consumption, a few studies have demonstrated a link (Headache, 1989).

Certain food additives can also trigger headaches and even migraines, so it is best to look for a short list of simple ingredients.

Digestive Issues

Among these meal replacement ingredients known to cause digestive side effects are food additives like emulsifiers, thickeners, and flavors.

Ultra-processed additives like these can cause bloating, constipation, diarrhea, and stomach pain.

They can also alter the composition of your gut microbiome (North Clin Istanb, 2019).

This can lead to gut dysbiosis, or an imbalance in gut bacteria, which is linked to the development of chronic digestion problems like irritable bowel syndrome (IBS) (Microorganisms, 2022; JGH Open, 2021).

Because your gut microbiome affects various physiological processes, including immune function and inflammation, when the balance of bacteria therein is disrupted, it can have a huge impact on your digestive health.

⚠️ 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

Note that this list includes several artificial sweeteners.

Artificial sweeteners like sucralose and acesulfame potassium are among the worst ingredients for your gut microbiome (Nature, 2014).

They both reduce microbial diversity and promote the growth of potentially pathogenic bacteria.

Also note that as a rule of thumb, if you could not find an ingredient in nature or make it at home, it is a food additive.

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

This is usually because they contain lactose, a sugar many people 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.

You should also consider avoiding protein concentrates and isolates.

Most meal replacements are made from one or both of these 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 can affect your gut health.

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

So instead of ultra-processed protein concentrates or isolates, look for whole food protein sources like egg whites and almonds.

They are easier to digest and absorb.

Order Samples to see for yourself.

Sources

1. Headache (Headache). Aspartame as a dietary trigger of headache. 1989.
2. Northern Clinics of Istanbul (North Clin Istanb). Food additives and microbiota. 2019.
3. Microorganisms (Microorganisms). Gut Microbiota Dysbiosis: Triggers, Consequences, Diagnostic and Therapeutic Options. 2022.
4. 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.
5. Nature (Nature). Artificial sweeteners induce glucose intolerance by altering the gut microbiota. 2014.
6. Nutrients (Nutrients). Effect of a Protein Supplement on the Gut Microbiota of Endurance Athletes: A Randomized, Controlled, Double-Blind Pilot Study. 2018.
7. 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.