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Food
Allergy
What
is food allergy?
"Food
allergy" or "food hypersensitivity"
are broad terms that encompass a range of
abnormal immune responses to foods. The
term "food allergy" is often misused
and can sometimes be confused with other
conditions that do not involve an immunological
response, for example food intolerance,
food poisoning, inborn errors of metabolism,
or digestive tract disorders1.
Food
allergies can be classed into four categories:
Type I, II, III IV hypersensitivities2.
Type
I
An
anaphylactic response involving IgE (immunoglobulin
E) which may result in runny nose, dilation
of blood vessels, swelling and breathing
difficulties. The reaction occurs almost
immediately and is potentially life threatening.
Type
II
Response
is immediate (as in Type I) and results
in cell damage.
Type
III
Reaction
occurs some hours later and involves the
skin and bronchi.
Type
IV
Delayed
reactions that can occur any time from 24
- 48 hours after exposure and may cause
a chronic inflammatory reaction. Type IV
reactions occur in approximately 95% of
food allergy reactions. Severity of symptoms
is usually dose related3.
(Ref: Anonymous, 19982)
There
appears to be an increase in the incidence
of food allergies in Western Society. It
has been suggested that the reason for this
increase is due to a reduction in challenges
to the immune system, which in turn causes
the immune system to overreact to small
stimuli2.
Symptoms
of Food Allergy
Possible
symptoms of food allergy are;
Itching and burning around the mouth and
local swelling
Gastrointestinal symptoms such as nausea,
vomiting, abdominal cramps and diarrhoea
Skin symptoms such as generalised urticaria
Respiratory symptoms (eg: wheezing and asthma)
Fatal anaphylaxis
Table
2 illustrates the different symptoms apparent
in Type I and Type IV hypersensitivities.
Table
2. Symptoms resulting in Type I and Type
IV hypersensitivities.
| Type
of hypersensitivity |
Symptoms
|
| Type
I |
all-or-none
reaction. Atopic dermatitis, urticaria,
gastoinstestinal allergy, analphylaxis
often permanent. |
| Type
IV |
Dose-related
severity of symptoms, symptoms usually
decrease in severity with prolonged
avoidance. |
(Source:
Zeman, FJ, 19915)
Allergenic
Foods
A
wide range of foods have been implicated
as causative agents in food allergies. The
most commonly reported include milk, eggs,
peanuts, fish, shellfish, nuts and fruit6.
In children, it has been reported that 91
percent of adverse reactions can be attributed
to four major foods, nuts, eggs milk, and
soy1.
Table 1 illustrates
the different characteristics of food allergies
and their associated foods.
Table
1. Foods involved in allergic reactions.
| Type
of hypersensitivity |
Onset |
Examples
of foods involved |
| Type
I |
Within
60 minutes of exposure |
Fish,
shellfish, nuts, legumes, eggs, milk,
berries |
| Type
IV |
Within
hours/days of exposure |
Milk,
wheat, chocolate, cola, corn, citrus
fruit, eggs, beef, white potatoes, pork,
legumes, chicken, oatmeal, rye, oranges,
cottonseed, mustard, tomatoes, cucumber,
garlic. |
(Source:
Zeman, FJ, 19915)
Diagnosis
of food allergy
Both
diet history and diagnostic testing are
important in determining the cause of food
allergies. The factors suggesting that the
allergy involves IgE include:
That specific foods can be identified
Symptoms occur shortly after food intake
Symptoms involve more than one organ (e.g.
swelling of mouth, nausea, vomiting, asthma,
abdominal pain, diarrhoea etc)
The patient has a personal or family history
of atopic disorders
(Ref: Bindslev-Jensen C. 19986)
Testing
for food allergies is usually conducted
by way of skin prick testing and in some
cases confirmed by an oral food challenge,
where small doses of the food are administered
under clinical conditions.
Treatment
Treatment
for food allergies involves avoidance of
the particular food causing the allergy.
This often requires the help of a dietitian
in order to train the patient to read food
labels to avoid the allergenic food.
Table 3 shows some
of the common allergenic foods and examples
of terms used on product labels.
Table
3. Food components and examples of terms
used on food labels.
| Food
Component |
Examples
of terms used on product labels |
| Milk
protein |
Milk,
cheese, yoghurt, non-fat milk solids,
caseinates, whey, milk, lactose |
| Lactose |
Milk,
lactose |
| Egg |
Egg,
egg albumen, egg yolk, egg lecithin |
| Gluten |
Wheat,
oats, barley, rye, triticale, cornflour,
gluten, wheat bran, oat bran, malt |
| Soy |
Soybeans,
hydrolysed vegetable protein, soy protein
isolate, soy lecithin |
| Salicylates |
Strawberries,
tomatoes |
(Source:
adapted from Briggs D.R. & Lennard LB.
1997 3)
References
(1)
DeBruyne LK, Rolfes SR, Whitney EN. Life
Cycle Nutrition. Conception through adolescence.
1989. 228-231. West Publishing Company,
MN, USA.
(2)
Anonymous. Adverse reactions to food. (Review).
Nursing Standard. 12(37):32-3, 1998 Jun
3-9
(3)
Briggs D.R. & Lennard LB. Food sensitivities.
Chp 43, 425-433 in Wahlqvist ML Food and
Nutrition, 1997, Allen & Unwin, NSW,
Australia.
(4)
Clarke L, McQueen J, Samild A, Swain A.
The dietary management of food allergy and
food intolerance in children and adults
- Dietitians Assocation of Australia Review
paper. Australian Journal of Nutrition and
Dietetics, 1996. 53:3. 89-98.
(5)
Zeman, FJ Clinical Nutrition and Dietetics.
2nd Edition, Macmillan, New York,
1991.
(6)
Bindslev-Jensen, C. ABC of Allergies. (Review).
British Medical Journal. 316(7140): 1299-1302.
April 25, 1998.
Other
resources
The Food Allergy
Network
US site with information about food allergy,
food allergy research studies and recipes.
International Food Information
Council
US site with on-line publications, questions
and answers and a listing of further resources.
US Food and Drug
Administration
Basic information on food allergies and
other resources.
Last
Updated: March 27, 2001.
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