Why am I sick after eating Quorn? The Truth About Mycoprotein

October 7, 2025 •

4 min read

According to reports submitted to the Center for Science in the Public Interest, thousands of consumers have reported adverse reactions after eating Quorn. If you've found yourself asking, "Why am I sick after eating Quorn?", the answer often points to a sensitivity to its main ingredient, mycoprotein, or its high fiber content.

Quick Summary

Adverse reactions to Quorn can be caused by either a gastrointestinal intolerance to its high fiber or a less common but serious allergy to its fungal protein, mycoprotein. Symptoms range from digestive upset to life-threatening allergic responses.

Key Points

Mycoprotein is the key ingredient: Quorn's core component is mycoprotein, a protein derived from a type of fungus, which can trigger adverse reactions in some individuals.
Intolerance linked to high fiber: Many gastrointestinal issues are caused by mycoprotein's high fiber content, which can ferment rapidly in the large intestine and cause discomfort.
Allergies are rare but serious: A true allergy to mycoprotein is less common but can lead to severe symptoms, including anaphylaxis.
Mold-allergy cross-reactivity: Individuals with mold allergies have a higher likelihood of reacting to mycoprotein due to similar protein structures.
Other ingredients may be the cause: Some Quorn products contain other allergens like eggs, milk, or wheat, so always check the label.
Consult a doctor for diagnosis: It is important to see a healthcare professional for proper diagnosis, especially if you suspect an allergy.
Symptoms differ between reactions: GI intolerance symptoms include vomiting and diarrhea, while allergic reactions involve hives, swelling, and breathing issues.

Understanding the Main Ingredient: Mycoprotein

At the heart of every Quorn product is mycoprotein, a protein-rich, fibrous ingredient derived from a type of fungus called Fusarium venenatum. While generally safe and well-tolerated by most people, some individuals can have adverse reactions, which can be categorized into two main types: gastrointestinal (GI) intolerance and a true allergic reaction. It is crucial to understand the difference to address your symptoms correctly.

Gastrointestinal Intolerance

For many who experience discomfort after eating Quorn, the culprit is the mycoprotein’s high fiber content, not a true allergy. Mycoprotein is particularly high in fiber, with approximately 5.5g per 100g of mince or pieces. While fiber is generally beneficial for gut health, this concentration can cause issues for certain individuals.

The Fermentation Process

In some people, consuming mycoprotein can speed up the normal passage of food through the small and large intestines. This accelerated transit allows the high fiber content to be fermented very rapidly by gut bacteria in the large intestine. The result is the production of gas and other byproducts that lead to gastro-intestinal distress. People who may be more susceptible to this rapid fermentation include those with conditions like Irritable Bowel Syndrome (IBS) or those with an existing imbalance in their gut bacteria.

Common gastrointestinal symptoms include:

Nausea and vomiting
Diarrhea
Abdominal pain or cramping
Headaches and sweating
General feeling of sickness

Allergic Reaction to Mycoprotein

A far rarer but potentially more serious issue is an actual allergy to mycoprotein. As mycoprotein is a fungal protein, those with sensitivities to other fungi, such as molds, may be more likely to have a reaction due to cross-reactivity. This is an IgE-mediated response where the body’s immune system overreacts to the mycoprotein, mistaking it for a harmful substance.

Symptoms of an allergic reaction:

Hives (urticaria) or rash
Swelling of the lips, tongue, or throat (angioedema)
Difficulty breathing or severe asthma
Feeling faint, dizzy, or sleepy
In severe cases, anaphylaxis

Cross-Reactivity with Molds

Cross-reactivity is a known phenomenon where the proteins in one substance (like mold spores) are similar enough to proteins in another (mycoprotein) to trigger an allergic response. For example, studies have shown that patients with a pre-existing mold allergy have reacted adversely to ingested mycoprotein. If you know you are sensitive to molds, you should exercise caution with Quorn products.

Other Potential Causes: Ingredients and Preparation

It is also possible that a reaction to a Quorn product isn't caused by the mycoprotein itself, but by other ingredients within the product.

Other common allergens: Many Quorn products are not completely vegan and may contain common allergens like egg, milk, or wheat. Always check the ingredient label carefully, especially if you have known allergies to these substances.
Cooking preparation: Improperly cooked or stored food can cause general food poisoning symptoms. Ensure that all Quorn products are cooked thoroughly according to the package directions.

Comparison: GI Intolerance vs. Allergic Reaction


Feature	Gastrointestinal (GI) Intolerance	Allergic Reaction (IgE-mediated)
Cause	High fiber content leading to rapid fermentation in the gut.	Immune system response to mycoprotein (fungal protein).
Onset	Usually occurs within a few hours of consumption.	Can occur very rapidly, sometimes within minutes.
Symptoms	Nausea, vomiting, diarrhea, abdominal cramps, gas.	Hives, swelling, difficulty breathing, dizziness, anaphylaxis.
Severity	Generally uncomfortable but not life-threatening.	Can be severe and potentially life-threatening (anaphylaxis).
Risk Factors	Conditions like IBS, sensitive gut, or imbalance in gut bacteria.	Existing allergies, especially to molds.

What to Do If You React to Quorn

If you believe you have had an adverse reaction to Quorn, taking the right steps is important. For immediate relief from mild symptoms like nausea or diarrhea, staying hydrated is key. However, for a proper diagnosis and safety, it is essential to seek medical advice.

Seeking Medical Advice

If you experience any severe symptoms, particularly those affecting breathing or causing swelling, seek immediate medical attention. For less severe but recurring symptoms, consulting a doctor or a registered dietitian is recommended. They may refer you for allergy testing, which can help determine if you have an allergy to mycoprotein or another ingredient. If an allergy is confirmed, avoiding Quorn products and foods containing mycoprotein is necessary. It's worth noting that mycoprotein may be used in food served at restaurants, so always inquire about ingredients.

Conclusion

While Quorn is a popular and nutritious meat alternative for many, it is not without risks for some individuals. The high fiber content of mycoprotein can cause gastrointestinal distress in those with sensitivities or underlying gut conditions. More rarely, a true IgE-mediated allergic reaction to the fungal protein can occur, which can be severe, especially for those with existing mold allergies. By paying close attention to your body's response and seeking medical guidance if needed, you can manage your diet safely. For more information on food allergies and intolerances, consult health resources like the Anaphylaxis UK website.

Frequently Asked Questions

Mycoprotein is the main ingredient in Quorn products. It is a protein-rich, fibrous substance derived from a fungus called Fusarium venenatum.

Yes, for some people, Quorn can cause digestive issues such as nausea, vomiting, diarrhea, and abdominal cramps. This is often due to its high fiber content, which ferments quickly in the gut.

No. An intolerance, often related to Quorn's fiber content, causes digestive discomfort but is not life-threatening. An allergy is a potentially severe, immune-system-mediated reaction that can cause hives, swelling, or anaphylaxis.

While rare, an allergic reaction to Quorn is more likely in individuals who have pre-existing allergies to other molds, due to a phenomenon called cross-reactivity.

If you experience symptoms like difficulty breathing, swelling of the face or throat, or dizziness, seek immediate medical help, as this could be anaphylaxis.

Yes. Some Quorn products contain other common allergens like egg, milk, or wheat. Always read the ingredient label to rule out a sensitivity to these other components.

If you experience mostly digestive symptoms (vomiting, diarrhea), it's more likely an intolerance. If you have skin reactions (hives) or breathing difficulties, it is more indicative of an allergy. The best way to know for sure is to consult a doctor for a proper diagnosis.