Asthma and food
Food or drinks are not common triggers of asthma. An unpleasant reaction to a food is more likely to involve your skin or digestive system than your lungs. A bad reaction to a food may be caused by either a true food allergy or, more commonly, a food intolerance.
What is the difference between food allergy and food intolerance?
A food allergy is when your immune system, that is, your body’s defence system, reacts abnormally to a food. The trigger for the allergic reaction is usually a protein in the food.
The symptoms of food allergy can include a rash or hives, sometimes vomiting, diarrhoea and abdominal cramps, and occasionally wheezing or difficulty breathing. These symptoms usually appear within a few minutes to one hour of eating the food. Less often, the symptoms may take a few hours to develop. The most severe form of food allergy, anaphylaxis, can be life-threatening.
A food intolerance — unlike a food allergy — does not involve the immune system. It is often caused by the chemicals in a food, either natural chemicals or those added as preservatives, colours or flavour enhancers.
Food intolerance causes symptoms such as abdominal pain, wind, diarrhoea and headache, and some additives, for example sulphur dioxide, can trigger asthma.
| Differences between food allergy and food intolerance | |
|---|---|
| Food allergy | Food intolerance |
| Involves the immune system. | Does not involve the immune system. |
| Symptoms include rash, hives, vomiting, diarrhoea, abdominal cramps and occasionally wheezing and difficulty breathing. | Can cause abdominal pain, wind, diarrhoea, headache and symptoms of asthma. |
| Symptoms usually appear a few minutes to an hour after eating the food. | Symptoms can appear within minutes of eating the food or more usually several hours, but can take up to 3 days to appear. |
| Food allergy can be mild or severe and in extreme cases can cause life-threatening anaphylaxis. | � |
| Examples of food allergy are allergies to nuts, fish, shellfish, eggs and sesame seeds. | � |
Food allergy
The allergic reaction can vary in severity, and in its most extreme form can rapidly produce life-threatening anaphylaxis (see box).
A food allergy that produces asthma symptoms is due to a particular type of allergic reaction called an ‘Ig-E mediated allergic reaction’. An IgE-mediated allergic reaction is so-called because it is brought about by IgE — immunoglobulin E — one of the body’s natural antibodies that is designed to fight disease-causing invaders such as gut parasites. In food allergy the IgE response has been redirected to produce a reaction to an essentially harmless food.
If you have a food allergy that triggers your asthma, when exposed to the food (the ‘allergen’) your IgE antibody goes into action and sparks a series of chemical reactions in your body’s tissues to ultimately cause airway narrowing. You will then get typical asthma symptoms such as wheeze, cough and/or difficulty in breathing.
Often an allergy to cows’ milk, soy, wheat or egg resolves by kindergarten age, but an allergy to nuts or seafood is likely to stay with you for life and cause serious symptoms if you come in contact with even the smallest amount of the food.
The most common foods that cause food allergy provoking asthma are:
- eggs;
- nuts;
- fish;
- milk;
- shellfish; and
- seeds (for example, sesame seeds).
| Food allergy and anaphylaxis |
|---|
|
FOOD ALLERGY: If you suspect that you or your child is allergic to a food or that a particular food has triggered an asthma attack, do not try the food again until you have seen your doctor. You may be referred to an allergy clinic for diagnosis and to a dietitian for dietary advice. ANAPHYLAXIS: Rarely, allergies to some foods, especially to nuts and shellfish, can rapidly produce a severe and life-threatening reaction called anaphylaxis. People suffering from anaphylaxis usually break out in a rash, feel their throat swell and close up and may feel dizzy and have trouble breathing. This is a medical emergency that needs immediate treatment. |
Food intolerance
You might find that you can’t eat certain foods without getting some unpleasant effects such as abdominal pain, wind, diarrhoea and sometimes headache. If this happens, you are likely to be intolerant of these foods rather than allergic to them. In some people a food intolerance can trigger asthma symptoms.
Symptoms can occur within minutes of eating a food (for example, a sulphite-containing food) or more often, several hours, even up to 3 days, after eating the food. Compare this with true food allergy, where the symptoms happen close to the time that you eat the food, within an hour, usually.
How to find out if you have a food allergy
Although knowing you have a food allergy can sometimes seem clear cut — you eat the food, you get symptoms within minutes — your doctor may want to investigate the allergy further. This may involve you going to an allergy clinic for skin prick tests or blood tests called radioallergosorbent tests (RASTs).
Your doctor will consider the results of these allergy tests as well as the type and timing of the symptoms you get after eating the food.
A positive test result for a particular food, with symptoms occurring soon after eating the food, will mean that this food is a likely trigger of your asthma. However, a positive result for a particular food without asthma symptoms occurring after eating the food means that, although you have antibodies to the food, it is not necessarily causing your asthma episodes.
A negative result for a particular food tends to rule out the food as a trigger of your asthma.
The National Asthma Council advises that unorthodox allergy tests such as Vega testing and kinesiology are unproven as methods of diagnosing allergies — you should see your doctor for allergy diagnosis.
Do food additives cause my asthma?
A food intolerance involving a food chemical is not always easy to diagnose because the symptoms can occur hours or days after eating the suspect food, and this type of sensitivity will not show up on the tests used to diagnose food allergy.
If you are intolerant of a food chemical, your response to the chemical depends on how much of it you eat, that is, eating a small amount might not make you sick, but a large amount is likely to produce symptoms. Again, compare this with a food allergy where eating even the smallest amount of a food, for example, peanuts eaten by a person allergic to them, can trigger a severe reaction.
Here are some of the food chemicals that can cause food intolerance, and in some people can trigger asthma symptoms.
- Sulphur dioxide and sulphites are used as preservatives in fruit juice or drink, wine, grapes, delicatessen meats and dried tree fruits such as apricots (food additive numbers 220 to 228). If you have severe asthma, talk to your doctor about whether to avoid foods that are labelled as containing sulphites. Sulphur dioxide (food additive number 220) is the most likely of the chemicals listed here to trigger asthma.
- Tartrazine (food additive number 102) is used as a dye in many foods — researchers are not yet sure if tartrazine triggers asthma.
- Salicylates are naturally present in most fruit and vegetables, and aspirin — the active ingredient in many pain-relieving medications — is a salicylate. At present, there is no evidence that people with asthma, even aspirin-sensitive asthma, should avoid naturally occurring salicylates in food.
- Glutamates, including monosodium glutamate (MSG), occur naturally in many foods or are added as flavour enhancers (food additive numbers 620 to 625). High amounts are present in Vegemite and soy sauce. However, studies have not proven whether MSG triggers asthma.
Royal Jelly
Royal Jelly is not a food but a complementary medicine that is made by nurse bees to feed the queen bee. It has caused severe allergy and even death in people with asthma and allergies. If you have asthma and allergies you should avoid this product.
The dairy myth
Cows’ milk allergy usually causes skin and digestive complaints rather than breathing difficulties or wheeze.
You might feel that your asthma comes on after drinking a glass of cold milk. However, this is thought to be caused by breathing in cold, dry air while drinking the cold milk, rather than by the milk itself.
Another myth surrounding milk is that it causes increased mucus in the airways. Milk does make the saliva in your mouth feel thick for a while, but studies have shown that it does not increase mucus production.
Avoidance diets — do they work?
Food allergies are often thought to be more common than they are and are often blamed for a range of problems, including asthma. However, eliminating foods such as eggs and milk from your diet will help only if you are allergic to eggs and milk.
Unless you have a diagnosed food allergy, eliminating a suspect food, for example milk, from your diet without checking with your doctor or having the allergy confirmed in a medically supervised test will probably not help you or your asthma. Eliminating foods can cause your diet to become deficient in important nutrients such as calcium — this is even more likely to happen in children.
Ask your doctor before eliminating foods from your diet or from your child’s diet.
A healthy balanced diet
If you have asthma, aim to maintain a healthy diet by eating a range of nutritious foods. Keeping fit and not being overweight will also help your breathing.
Unless you have specific advice to avoid particular foods from your doctor, allergy specialist or dietitian, follow a healthy diet as recommended for all Australians by the National Health and Medical Research Centre:
- limit fat and sugar;
- eat plenty of breads and cereals, preferably wholegrain;
- include dairy foods (preferably reduced-fat varieties), fish, lean meat, nuts, legumes and eggs in your diet;
- eat more fruits and vegetables;
- drink plenty of water; and
- limit foods that are high in salt.
Last Reviewed: 04 September 2007
