Sue's Blog

What is MCAS?


Guest blog from Food Intolerance dietitian Liz Beavis APD

There has been a lot more awareness about Mast Cell Activation Syndrome (MCAS for short) recently, which has left a lot of people wondering - what is MCAS? And do my symptoms mean that I have MCAS?

Symptoms of Mast Cell Activation Syndrome can include

• rashes, itching skin or flushing
• itchy, watery eyes
• runny nose
• swelling, inflammation
• headaches, brain fog
• rapid heart beat
• fatigue
• diarrhoea, constipation or abdominal pain
• wheezing
• anaphylaxis

Mast cells are one type of immune cell that release histamine (as well as other mediators) when they are triggered, so many of the symptoms are related to a surge of histamine.

Mast Cell Activation Syndrome is, in some ways similar to an allergy (like peanut or grass pollen allergy). However, instead of your immune responding to just 1 type of allergenic trigger, it can respond to a whole range of triggers, which can be different for each person and often seemingly random.

Can a Low Chemical Diet help with MCAS?

Yes, a low chemical diet (eg Failsafe Diet) reduces your intake of histamines and can help reduce histamine-triggered symptoms, although for many people with MCAS you will also need some additional strategies.

Histamine is one of about 20 different groups of amine compounds. In a low chemical diet these are all categorised together as ‘amines’ to keep things simple, as many of the amine groups share similar pathways in your body so symptoms are often triggered by more than one of the amine groups. I’m going to focus on histamine in this article, but in most places I have mentioned 'histamine' you can replace this with ‘amines’ to keep the bigger picture in mind.

To take a step back, there are three main sources of histamine in your body:

First, your diet contains many foods that are naturally rich in histamines and other similar amine groups (one of the things that makes our food so tasty!). This is your dietary histamine/amine load.

Second, some of your gut bacteria produces histamine and other amines. Some people have particularly high levels of these bacteria. I’m going to call that microbial histamine.

Third, your Mast Cells release histamine when they are triggered - lets call this your Mast Cell Histamine. This may be a small amount in a local area (eg a red itchy circle around a mosquito bite), a larger amount eg that triggers hayfever symptoms, or a really large amount that can trigger more extreme symptoms like rapid heart-rate, fainting or anaphylaxis.

All of the histamine (from all three sources) contributes to your histamine load. Some people describe this as your 'Histamine Bucket'. Some people have a smaller bucket, some people have a larger bucket (more on why this happens, and how you can increase your bucket size, another day!), but regardless, your Bucket will be filled with histamine from all three sources.

When you reduce your dietary histamine/amine load on a Low Chemical Diet you are reducing the amount in your histamine bucket, which may help to reduce symptoms caused by high histamine levels, regardless of which of the three sources of histamine were filling your bucket. This is an easy first step, and for some people can improve their symptoms significantly whilst you work with your healthcare team to understand the underlying reasons.

If you have histamine/amine overload issues (because your histamine/amine bucket is small) you need to work to increase your bucket so you can include more amine foods without triggering symptoms. You can also reduce your microbial histamine so your bucket doesn’t fill up so easily.

If you have MCAS, reducing your histamine load and increasing your bucket size will be helpful to reduce symptoms, but may not be enough. You will also likely benefit from addressing the Mast Cell Activation directly so that you reduce how much Mast Cell histamine is released, which will also help to reduce the amount in your bucket. Your MCAS specialist practitioners will be able to help you reduce histamine release and reduce your symptoms with medications and/or supplements.

It is so exciting to see more practitioners with an understanding of MCAS, a condition that was relatively unknown a few years ago, so many more people are getting the support that they need for such a confusing health issue.

The only downside is that I think we are also seeing over-diagnosis of MCAS in some situations where the real problem is high microbial histamine or small histamine bucket, which I think should be addressed before assuming all high histamine symptoms are due to MCAS.

Top tips for understanding MCAS

• A low histamine diet will help to reduce your MCAS symptoms
• A sensitivity to histamine (or amines) doesn’t always mean you have MCAS
• Trial a low chemical diet (rather than just low histamine) as other food chemical intolerances are often also present
• Work with a dietitian as your triggers may be more complex
• Work with your practitioner to understand any underlying issues that may be contributing to your symptoms.