Professor Frank Thien discusses food allergies and intolerances and their link with asthma and anaphylaxis
Asthma is a common condition affecting almost three million Australians and resulting in over 70,000 emergency visits annually.
Given the links between foods and many medical conditions, many asthma sufferers and their carers want to know about the link between food and asthma.
Professor Frank Thien, a respiratory physician with Eastern Health and Monash University Clinical School, is a member of the Thoracic Society of Australia and New Zealand (TSANZ) and the Australasian Society of Clinical Immunology and Allergy (ASCIA).
One of Professor Thien’s main research interests is the study of severe asthma. In this Q&A, Professor Thien and I dissect the nuances regarding food allergies and asthma.
John Weiner (JW): Let’s start with asthma and anaphylaxis. How often is bronchospasm a part of the anaphylaxis syndrome caused by foods and how is it managed in this scenario?
Professor Frank Thien (FT): Asthma or bronchospasm can be a manifestation of any episode of anaphylaxis, including food-induced anaphylaxis, but tends to be part of a more severe reaction.
The initial management of anaphylaxis is intramuscular adrenaline and volume expansion with intravenous saline. The adrenaline will often relieve bronchospasm, and in fact was used as first aid treatment in asthma for many years during the last century. Persistent bronchospasm despite this initial treatment may respond with the usual bronchodilators.
JW: Is anaphylaxis more dangerous if a person has asthma?
FT: Yes, fatal or near-fatal anaphylaxis is often due to bronchospasm in someone with pre-existing asthma. The risks are increased if the asthma is not well controlled, or not being treated with preventer/anti-inflammatory medication such as inhaled steroids.
JW: Results from surveys report that up to 70% of people claim that some foods trigger their asthma. What do you feel is the true proportion of asthma that is triggered by food intolerance and how is food intolerance diagnosed?
FT: Food intolerance, as opposed to true food allergy, cannot be diagnosed by skin or blood tests. It requires a careful history, and a trial of elimination/exclusion diet, followed by graded rechallenge. I should add that even though most of these episodes are relatively mild, if any food is suspected of causing some degree of wheezing, then the diet and challenges should be supervised by an allergy clinic, often with the assistance of a qualified dietitian.
Using this approach, the true proportion of asthma caused by food intolerance may be in the range of 5–10%, depending on the age group.
JW: Patients and their carers often complain about the length of time it takes to see an allergist or obtain an appointment with an allergy clinic. However, there are blood tests available through most pathology laboratories that claim they can confirm food intolerance with no need for a doctor’s request form. Can you comment on these tests?
FT: Those blood tests are called Immunoglobulin G (IgG) food tests. They purport to diagnose an intolerance to foods and food additives, but there is no role for IgG food tests in the diagnosis of allergy or food intolerance.
IgG and IgE are different entities. IgE is the antibody utilised in skin tests and blood tests for true allergy and can therefore pick up true immediate hypersensitivity. But IgG only transiently increases on eating food, so some IgG antibodies exist in everyone, and there is no evidence that this increase in IgG points to any degree of food allergy or intolerance.
I do appreciate the difficulty in obtaining an appointment with an allergist or an allergy clinic and would recommend that anyone who feels they have an intolerance to a particular food or food additive discuss it with a certified dietitian and ask the dietitian for advice on how to avoid that particular food or food additive until it can be scientifically and properly tested in an allergy clinic.
I should add that IgG food tests go by many different trade names. Very often large numbers of foods (often 100 or more) are claimed to be diagnosed using one small sample of blood, even a pinprick. These tests often cost hundreds of dollars with no rebate.
I repeat, there is no role for IgG food testing in the diagnosis of any sort of food allergy or food intolerance. IgG is the antibody utilised in some immunodeficiencies, some immune complex diseases, and in the diagnosis of coeliac disease (which is an autoimmune disease, not an allergy).
JW: Finally, I have some questions about asthma and sulfite allergy. Is sulfite a true allergy, and which foods contain sulfites?
FT: I would refer to it as sulfite intolerance rather than allergy. Sulfite is added to some foods as a preservative. Allergy is a hypersensitivity reaction mediated by immunological mechanisms (allergic antibodies and immune cells). Sulfite intolerance is an intolerance reaction most likely caused by pharmacological mechanisms.
De novo asthma is rarely the initial presentation of sulfite intolerance, and it more commonly affects people with pre-existing asthma. It is estimated to affect 5–10% of people with asthma. Some people are much more susceptible to sulfite as a trigger for wheezing when their asthma is poorly controlled. In the same way, poorly controlled asthma will make wheezing more common after exposure to any environmental pollutant.
For more information on sulfite sensitivity and asthma, I recommend the sulfite sensitivity FAQ put out by ASCIA (allergy.org.au/patients/other-allergy/sulfite-sensitivity-faq)
John Weiner is a retired consultant physician and pathologist, and member of the Allergy & Respiratory Republic editorial board. He is a freelance healthcare and science journalist.
