A food allergy is basically an immune response to proteins in the
respective food. This is twice as common
in children (up to 8%) as adults (4%).
For children, the most common food allergens are milk, egg, peanut, soy,
wheat, and tree nuts, in descending order of frequency. In adults, fish, shellfish, peanut, and tree
nuts are most common causes of allergic reactions. These may also be lifelong
allergies. They may manifest as an
immediate and life-threatening condition, such as anaphylaxis, or as a delayed
or chronic condition, like an atopic dermatitis (eczema), and are referred to
as “IgE-associated food allergies”.
There are also food-protein induced forms of enterocolitis and
proctitis, which are caused by “non-IgE” mediated mechanisms. Finally there is eosinophilic esophagitis and
gastroenteritis, which are due to a mix of IgE and non-IgE mediated
causes.
There are other types of food-induced problems, which are not
allergic, such as migraine headaches that are brought on in some patients by
tyramine containing foods like chocolate, cheese, some wines and beers. Lactose intolerance is not a true food
“allergy” but a form of osmotic diarrhea caused by a genetic absence of the
lactase enzyme that normally breaks down the milk sugar.
Gluten or wheat allergy is a true immune reaction in patients
with a genetic predisposition. Gluten
allergy also includes rye, barley and sometimes oats, because the latter is
processed in the same plants. This
reaction destroys the villi in the mucosa of the small intestine where most
absorption takes place. The result is
malabsorption of nutrients. Symptoms
include diarrhea, fatty and floating malodorous stools, weight loss, abdominal
distention, weakness, muscle wasting or growth retardation (in infants). This is referred to as celiac disease. There also is a lesser and poorly described
“intolerance to gluten” which is usually a milder condition but is probably not
an immune reaction.
A detailed dietary history within the 24 hours of allergic
symptoms may provide the best clues to food allergy, with particular attention
to other allergic history and prior reactions. Diagnosis is often difficult,
however, and it may require multiple episodes before an offending agent is
identified. Symptoms of food allergy include swelling and itching of the lips,
mouth, and pharynx; nausea; abdominal cramps; vomiting; and diarrhea. Cutaneous
manifestations, such as angioedema and urticaria, as well as anaphylaxis, can
occur. Treatment for mild reactions is supportive, with the administration of
antihistamines to lessen symptoms. More severe reactions or anaphylaxis are
managed differently.
The best treatment for food allergy is to avoid the food in
question, especially if very severe allergic reactions occur. However, it may
not always be a simple matter to avoid a given food, particularly outside the
home, and for this reason, those who are seriously affected by food allergies
are usually advised to carry a self-injector containing epinephrine, which can
counter serious symptoms, including bronchospasm.