Low Histamine Diet for Long COVID – Are Mast Cells Involved?

While the early unknowns of the COVID-19 pandemic are behind us, we still have a lot to learn about the long-term effects and pathophysiology of the COVID-19 virus. In particular, we are only beginning to research and understand a phenomenon called ‘Long COVID’ – also known as post-COVID-19 syndrome. 

Recently, there have been connections made between long COVID and mast cell activation syndrome (MCAS), as they share similar symptoms. This has led to an interest in using the low histamine diet to improve long COVID symptoms. As a whole, we need many more studies on the link between these conditions before we can draw conclusions – but it’s an interesting topic, and one that has garnered some attention as to how diet may help. 

Of course, as a registered dietitian who works with MCAS patients and food sensitivities, I’m keen to learn more about this link. In my own clinical practice, I’ve also had long COVID patients who notice this relationship, in addition to those who have developed MCAS, and food allergies or intolerances post COVID. So how can food play a role in the management of long COVID with suspected mast cell activation? First we need to understand the similarities and differences between these two conditions. 

What is Long COVID?

According to the National Health Service, long COVID (post-COVID-19 syndrome) is defined as having ‘signs and symptoms that develop during or after an infection consistent with COVID-19, continue for more than 12 weeks’ – they also clarify that these symptoms are unable to be explained by a different diagnosis.¹ 

What are the symptoms of Long COVID?

The symptoms of long COVID generally present as a cluster of multiple symptoms and can impact different areas and functions of the body.¹ Symptoms can include the following:

• Extreme fatigue
• Shortness of breath
• Chronic cough and/or sore throat
• Taste and smell changes
• GI issues such as diarrhea, indigestion, abdominal pain, and bloating
• Chest pain/heart palpitations
• Skin rashes/hives
• Brain fog or dizziness
• Headaches
• Tinnitus/earaches
• Joint pain
• Insomnia and difficulty sleeping
• Nutritional deficiencies

Since this is such a wide net of symptoms – it is important that other possible diagnoses be ruled out, as symptoms do overlap with numerous other conditions.

What is Mast Cell Activation Syndrome?

Mast cell activation syndrome (MCAS) is a condition in which patients experience allergy-type symptoms repeatedly, but aren’t actually having an IgE-mediated allergy. This is caused when mast cells in the body release chemical mediators. One mediator that we hear about often is histamine – a chemical that the cells release during an allergic reaction. 

It’s important to note that all humans have mast cells, but typically they remain ‘unactivated’ unless experiencing something that signals the immune system to respond – like an IgE allergic reaction to an allergen. They can also be activated by infections, certain medications, or exposures to venom or poisonous substances. In short, the job of the mast cell is to send out protective substances when necessary. 

In MCAS, these mast cells are activated more spontaneously or because of abnormal signals in the body – ie. not just in those “typical” scenarios like allergies. This can lead to allergy-type symptoms including skin rashes and hives, breathing difficulties, neurological changes (brain fog, confusions, headaches), fatigue, GI upset, and more.² 

Long COVID and MCAS: A Possible Relationship

It’s not difficult to see the similarities between long COVID and MCAS. However, as I’ve mentioned several times in this post, we still don’t have a lot of information on the possible link. Both MCAS and long COVID are pretty new conditions that are still lacking a lot of research. 

Due to the largely similar cluster of symptoms between these two diagnoses, it has been hypothesized that systemic inflammation seen in long COVID could be in part mediated by mast cell activation. This may mean that interventions for MCAS symptom management could be helpful for long COVID patients as well. 

I Have Long COVID and Want to Explore MCAS – Now What?

If you are someone who has many of the overlapping symptoms of long COVID and MCAS, talk to your doctor about getting the proper diagnosis. For starters, it’s best to rule out other potential causes of symptoms, particularly IgE-mediated allergies. This often means getting referred to an allergist or immunologist. 

If your symptoms reflect those of MCAS, your physician may consider trialling medication management to see if you respond. This is called ‘empirical treatment’ – it can be hard to diagnose MCAS so medications may be trialled instead.  Some medications include:

• H2 blockers
• Leukotriene receptor antagonists
• Mast cell stabilizers

Positive response to medications may help the doctor determine a diagnosis.

Can nutrition changes help with long COVID?

The short answer – maybe. But we have a lot more to learn. 

The long answer – it likely depends on the type of symptoms that a patient with long COVID experiences. In particular, if they have symptoms that overlap with MCAS, and notice symptoms especially with certain types of foods, a low histamine diet may provide some relief. However, not every person who “fits the bill” should be put on a restrictive diet, as there are many other things to consider. Is there a history of eating disorders or disordered eating? Are they having a difficult time eating enough as it is? Are they deficient in important nutrients? These are all scenarios where pursuing a restrictive diet wouldn’t likely be appropriate. 

The Low Histamine Diet for Long COVID

Following a low histamine diet is often helpful for managing MCAS symptoms, as it reduces the amount of histamine coming into the body during a time when the mast cells are releasing excess histamine. Given the theories that mast cell activation could be involved in long COVID, the low histamine diet could potentially help with this condition as well. 

Many foods are naturally quite high in histamine or release histamine in the body. Therefore contributing to the histamine “bucket”. Therefore, it may be beneficial to limit intake of said foods in order to reduce the allergy-type symptoms mentioned above. However, there is no such thing as a ‘no histamine diet’. The purpose of this approach is to lessen the intake of histamine, not to fully eliminate it. 

As dietitians, one of our top priorities is to ensure our patients’ diets are the least restrictive possible. Following a low histamine diet for long COVID is no different. Our goal is to reduce the intake of high histamine foods in order to improve symptoms – without being too restrictive. The goal of the low histamine diet is not simply just symptom relief, but also better understanding of tolerance to foods. We work with our patients to gradually and strategically add things back. This helps us to identify how much histamine they are able to tolerate. 

Due to the nuance of this diet, it is highly recommended to work with a registered dietitian experienced with the low histamine diet.