If you’re struggling with unexplained symptoms like fatigue, flushing, bloating, rashes, anxiety, or food reactions, you may have come across MCAS (Mast Cell Activation Syndrome) and histamine intolerance. These two conditions can look almost identical on the surface — yet their underlying causes are quite different. Understanding this distinction is key to finding the right diet and lifestyle strategy for your body.
MCAS occurs when mast cells, a type of immune cell involved in inflammation and allergy responses, become overactive. These cells release large amounts of histamine, prostaglandins, leukotrienes, and cytokines, even when there’s no real threat.
Because mast cells are found throughout the body, symptoms can affect multiple systems — skin (hives, itching, flushing), digestion (bloating, nausea, diarrhea), the cardiovascular system (palpitations, dizziness), and even the brain (anxiety, fatigue, brain fog).
Common triggers include infections, chronic stress, environmental toxins, mold exposure, hormonal shifts (especially high estrogen), and gut imbalances such as SIBO. MCAS is therefore a multi-system immune dysregulation, not simply a reaction to high-histamine foods.
Histamine intolerance, on the other hand, happens when there’s too much histamine in the body compared to your ability to break it down. The enzyme DAO (diamine oxidase), produced mainly in the intestinal lining, is responsible for degrading histamine from foods.
If DAO activity is low — due to gut inflammation, SIBO, medications, nutrient deficiencies (vitamin B6, copper, vitamin C), or estrogen dominance — histamine builds up and causes symptoms such as headaches, flushing, congestion, anxiety, digestive upset, or insomnia.
In this case, the issue isn’t mast cells being overactive, but rather a clearance problem: histamine is not being broken down efficiently.
Think of your body’s ability to handle histamine like a bucket. Every source of histamine — whether from food, stress, hormones, infections, or gut imbalances — fills the bucket a little more. Once it overflows, symptoms appear.
For some people, the bucket fills mainly from food-derived histamine (due to low DAO), leading to histamine intolerance. For others, it’s mast cell overactivation caused by immune dysregulation, chronic infections, or toxic exposures, resulting in MCAS. In many cases, both mechanisms coexist — which is why it’s so important to look at the whole picture rather than treating one label.
From a nutritional therapy perspective, both conditions benefit from a personalised approach that supports the gut, balances hormones, and stabilises the immune system. Some key steps include:
Short-term low histamine diet: This can help reduce symptom load while deeper healing takes place.
Gut repair: Addressing SIBO, dysbiosis, and leaky gut improves DAO production and reduces inflammation.
Nutrient repletion: Supporting DAO activity with vitamin C, B6, copper, and magnesium can help histamine clearance.
Mast cell stabilisation: Nutrients and compounds such as quercetin, vitamin C, and omega-3s can help calm mast cell activity.
Hormone balance: Managing estrogen dominance through liver support and stress management reduces histamine overload.
Because MCAS and histamine intolerance can overlap — and each person’s triggers are unique — identifying which condition is driving your symptoms often requires a functional and personalised assessment.
Working 1:1 with a nutritional therapist allows for:
Tailored testing for DAO activity, gut health, or mast cell mediators
Identification of root causes such as infections, mold exposure, or hormonal imbalance
A step-by-step nutrition plan that restores tolerance rather than just restricting foods
This is not a one-size-fits-all journey. A trained practitioner can help you understand your body’s “histamine bucket,” rebuild resilience, and design a diet for MCAS or low histamine diet that supports long-term healing without unnecessary deprivation.
If you’d like personalised guidance to uncover your root causes and design a nutrition plan tailored to your symptoms, you can book a free discovery call to understand how I can help you or explore my MCAS and Histamine Intolerance Nutrition Support programs.
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