Food Intolerances, Weight Gain, and Scent Sensitivity? It may be Mast Cell Activation Syndrome (MCAS)
- Terri Edwards
- Jul 1
- 3 min read
What Is Mast Cell Activation Syndrome (MCAS)?
If you’ve been experiencing allergic responses for years - dealing with symptoms like sneezing, food sensitivities, reactions to exercise, temperature, or scents – and nothing fully resolves the symptoms, it might actually be mast cell activation syndrome.
Mast cell activation syndrome (MCAS) is a disorder of the immune system where mast cells - a type of white blood cell – inappropriately release inflammatory chemicals, such as histamine, heparin, and prostaglandin D2 (PGD2), with episodes occurring without any obvious or external threat (1).
Since mast cells are present throughout most of the body, symptoms of MCAS can include many systems, such as gastrointestinal (diarrhea, abdominal pain, and cramping), musculoskeletal pain, and itching, flushing, or hives of the skin (2).
Diagnosis is complex, with physical exams, symptom history, and specific testing (blood and urine) that show elevated mast cell mediators during episodes (3).
MCAS flares can be triggered by a variety of physical or emotional stressors, such as temperature changes, exposure to odors, hormonal shifts, viral, bacterial, and fungal illnesses, medications, and even insect bites (2).
MCAS and food intolerance
When an individual has MCAS, food intolerance/allergy can present with reactions like headaches, gastrointestinal issues (bloating, gas, abdominal pain), hives, and anxiety, as the food itself becomes a trigger to the underlying issue of MCAS (4).
Mast cells are highly concentrated in the GI tract, which can make certain foods, like high-histamine and histamine-triggering foods (cured meats, fermented vegetables, citrus, and tomatoes), triggers for symptoms (4) (5).
Consuming foods the body is intolerant to will contribute to inflammation and mast cell degranulation, and prevent the body's ability to achieve tolerance to that food (7) (6). A temporary elimination of foods that trigger a reaction can help reduce damage from the inflammatory process and support the body's healing process (6).
Things to keep in mind with food triggers:
Most individuals can’t avoid all food triggers (FODMAPs, oxalates, lectins, salicylates) and achieve adequate nutrition
Keep as many nutrient-dense foods in your diet as you can; some foods may only need to be limited – keep track of reactions (food journal)
Food swaps can be helpful – like apples (low histamine) for bananas (high histamine)
Remember to add foods back as you heal – dietary changes are a temporary support
Histamine food intolerance tends to be common with MCAS - lowering high-histamine food intake can be a good place to begin (8)
MCAS and weight gain
Mast cells are largely present in fat tissue (white adipose), and studies show that they participate directly in conditions like obesity and diabetes, as the chronic activation of mast cells disrupts hormones that regulate metabolism, appetite, and fat storage (9).
For example, inflammatory mediators such as IL-6 and histamine, released by mast cells, can interfere with insulin receptors and prevent cells from taking up glucose, leading to elevated blood sugar and, over time, insulin resistance and increased fat storage (10).
MCAS often presents with symptoms like fatigue, pain, and food reactions that lead to a more restrictive diet, which, over time, reduces the individual's ability to get sufficient movement or exercise, and nutrient deficiencies that can lead to unwanted weight gain and further dysfunction in the body (11) (12).
Avoid symptom triggers (foods, stress, etc.)
Trial a low-histamine, gluten- and dairy-free diet (3 weeks) to reduce mast cell burden
Nutraceuticals (natural mast cell stabilizers) like quercetin, resveratrol, and vitamins C and D may help
MCAS and scent sensitivity
Chemical and scent sensitivities are very common with MCAS, with about 60% of MCAS patients experiencing chemical intolerance (15). Exposure to volatile organic compounds (VOCs) such as air fresheners, chlorine bleach, perfumes, glue, and permanent markers can trigger mast cells to release inflammatory mediators, like histamine, leading to symptoms in those with MCAS (15).
An intolerance to chemicals, such as VOCs, medications, and pesticides, can result from Toxicant-Induced Loss of Tolerance (TILT), which occurs when an initial exposure triggers intolerance to subsequent exposures to these chemicals (15). TILT can lead to conditions like cardiovascular disease, skin conditions, and depression and anxiety (15).
Acting as sentinel immune cells, mast cells respond when environmental toxins, such as VOCs, enter the body by releasing mediators, including histamine, to trigger a protective inflammatory response (16). This is one reason why MCAS is thought to be a key biomechanism in many chronic conditions today.
Stabilize mast cells (luteolin, quercetin, etc.)
Reduce local inflammation
Avoid triggers
Nutraceuticals and natural anti-inflammatories that can be helpful: berberine, spirulina, green tea, curcumin, quercetin, and vitamin C
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