Soy is a staple ingredient in many households, whether in the form of tofu, soy milk or condiments like soy sauce. But for people with systemic mastocytosis (SM), soy can raise some concerns.
Mast cells in SM release large amounts of histamine, a chemical that drives symptoms ranging from flushing and itching to abdominal pain, headaches and fatigue. Because certain foods naturally contain high levels of histamine (or trigger its release), diet can play a major role in symptom control.
Whether or not soy triggers symptoms in people with SM actually depends less on soy itself and more on how it’s prepared. Here’s a closer look at what you should know about soy and SM.
Soy and histamine: What’s the connection?
Soybeans on their own are relatively low in histamine. The issue arises when they’re fermented.
Fermentation, a process that relies on bacteria or fungi to break down food, significantly boosts histamine levels. For someone with SM who is already sensitive to histamine, eating fermented soy can easily tip the balance and worsen symptoms.
Learn more about SM signs and symptoms
What foods have fermented soy?
You may already know that soy sauce is fermented, but there are several other common soy-based foods that also fall into this category. They include:
- Miso – fermented soybean paste used in soups and sauces.
- Tempeh – a protein-rich, fermented soybean cake.
- Soy sauce and tamari – popular condiments in Asian cooking.
- Natto – a strong-smelling, sticky fermented soybean dish from Japan.
- Soy-based pastes or seasonings – sometimes found in marinades and packaged sauces.
Because of their higher histamine content, these foods are more likely to trigger reactions in people with SM.
Safer soy options for systemic mastocytosis
Not all soy foods are high in histamine. Many are unfermented and contain much lower levels of the chemical, such as:
- Tofu – fresh unless labeled as fermented.
- Soy milk – especially when freshly made and stored properly.
- Edamame – steamed or boiled green soybeans.
- Soy protein powders – though labels should be checked for additives.
These soy foods are often better tolerated by individuals with SM, but keep in mind that sensitivity varies widely from person to person.
Soy and your diet
Whether or not you should avoid soy (particularly fermented soy foods high in histamines) will depend on your body’s own responses. The safest approach is to test foods gradually and pay attention to how you feel. Be sure to read labels carefully, as fermented soy products can appear in packaged foods under different names.
Keeping a food diary can help spot patterns, and working with a registered dietitian who understands mast cell disorders can provide additional support and guidance.
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