FOOD ALLERGY
There is likely no area that is as badly
misunderstood as that of true food allergy. Many adverse reactions to foods
have been blamed on allergy. Many examples exist : drinking too much caffeine
and getting a tremor, nausea, etc.; eating tyramine containing foods (red wine,
some cheeses) and getting a migraine headache, and so on. Similarly,
toxic reactions to food have been blamed on allergy (for example: ingesting
certain seafood contaminated with a variety of toxins). Please go back to the
start of the Allergic Respiratory Diseases section and review the basic
Allergic Process prior to continuing here.
While there are occasional delayed reactions
to foods, the usual IgE mediated reaction to food occurs within seconds to
minutes, and certainly usually within an hour. Immediate (within seconds) food
reactions usually are fairly evident. If every time you try to eat a peanut,
your lips and mouth swell and get itchy, you likely are allergic to peanuts.
The common reactions to food allergy usually occur in the skin or digestive
system: having your lips swell, developing hives or a red itchy rash on the
face or the rest of the body, eczema appearing or getting worse, tongue and
throat swelling or getting itchy, abdominal cramps, vomiting, diarrhea, and so
on. If multiple systems are involved in the reaction, particularly the chest
(wheezing, difficulty breathing) or the vascular system (fainting, pale, weak
and sweating) this reaction represents anaphylaxis. However, many food
allergies only cause skin or abdominal symptoms.
The most important point to remember is that
any suspected food allergy must be confirmed with appropriate testing. There
are very few exceptions to this rule, the only exception should be an ultra
severe life threatening anaphylactic reaction to a specific food coupled with a
clear cut history, where avoidance of this food has prevented any further
reactions. I will give you an example to illustrate this point. An individual
goes to a restaurant, eats an entire dinner, which included shrimp, and
immediately after the dinner developed a generalized rash and had vomiting and
diarrhea. If this person goes to the average emergency
department, after appropriate treatment, they will be told to avoid shrimp and
are given a prescription for an EpipenTM. For the rest of this person's life, they avoid shrimp
and possibly all seafood. This individual should always be tested to prove they
are allergic to shrimp. In this particular case skin testing was totally
negative to shrimp and all seafood. Negative skin testing is highly accurate
for most foods in proving no IgE allergy exists, particularly, if fresh food is
used for the skin testing. This individual did have a major positive skin test
to Anisakis Simplex - a seafood parasite - a common
cause of "seafood allergy". This person can continue to enjoy shrimp
and other seafood, however, must be prepared to treat an allergic reaction as
they may eat seafood contaminated with this parasite in the future. The bottom
line is that things are often not what they seem in food allergy. The other
point is that patients are seldom shown how to use an EpipenTM , and are never capable of using it properly during an
emergency situation. Unless someone
clearly understands how to use their EpipenTM under normal circumstances, they certainly will never
use it properly during an emergency situation. I have every patient demonstrate
how to use their EpipenTM
when I initially see them in my office, and over 90% do not demonstrate correct
technique. Skin testing is used to confirm a previous reaction to a food as
being truly allergic or can guide dietary manipulation and testing to see if a
specific positive skin test indicates true food allergy. This is very important
to understand. Many individuals will develop positive skin tests to cow’s milk
when they first encounter cow’s milk as a baby, and this skin test persists as
positive for many years. Many of these people never had any clinical allergy to
cow’s milk and can drink milk with no problems. The point being made is that
having a positive skin test to a food must not be interpreted as indicating
clinical allergy AND must have the appropriate dietary manipulation done to
prove that true allergy exists.
The ideal way to prove food allergy is to
perform a double blind placebo controlled food challenge (DBFC). In this
testing the person taking the suspect food and the investigator giving the food
challenge do not know the contents of each capsule (usually capsules are used
so the patient cannot taste the food) and the results are interpreted by a
third party who knows the actual contents of each capsule. Placebo reactions to
foods are exceedingly common where an individual is so afraid or convinced of a
specific food that they experience symptoms eating a suspect food (when the
actual food eaten was not what they thought it was). There are two chief
problems with this procedure. The first is that this is an extremely expensive
and time consuming procedure. The second is that certain food allergies wax and
wane (in other words, at certain times an individual can experience an allergic
reaction to a specific food and at other times will eat that food with no
symptoms evident). The good point of DBFC is that it clearly shows which
individuals are experiencing placebo reactions and these individuals can be
clearly told they do not have to avoid this specific food. Perhaps the greatest
risk of food allergy diagnosis is that an individual will avoid a specific food
(often a very important food from a nutritional point of view) for prolonged
periods of time risking malnutrition and inadequate diet.
TESTING SPECIFIC FOOD(S)
So how do we attempt to diagnose food allergy
in a practical way. If you have had a
severe-anaphylactic reaction to a food you should have a clear cut positive
skin test to that particular food, with negative skin tests to a variety of
other foods.
If you
have less specific reactions (for example mild itching, abdominal bloating,
occasional diarrhea) I usually skin test suspected foods first. If there are several positive skin tests to
foods that could fit the specific history or if the patient is convinced a
specific food may be causing a problem, I have the patient complete an
elimination-rechallenge diet at home. Note:
this cannot be done if you suspect severe allergy. The process is quite simple. The patient
strictly avoids a specific food for one week (occasionally longer). It is absolutely critical that the suspect
food be strictly avoided, and this is where the major problem lies. Many
individuals cheat on their diet or unknowingly eat the food to be avoided (for
example in a sauce, remembering that food labeling in
If the patient is having bowel problems and
the question being asked is – “Could foods be playing a role in my bowel
problem” – then a full elimination diet is often performed. There is a subsection in this Contents section
that reviews aspects of the Elimination diet. Essentially, I have the patient avoid all
possible allergenic foods for 1 week. This
often means a very restricted diet of water, salt, rice, chicken
for a week or some variation of this. If
this diet is adhered to completely (very difficult) and there is one or more
foods causing bowel problems, the bowel problems will disappear after 2 days on
this diet. If (and only if) clear
improvement is seen, then we start on a reintroduction phase, adding in one new
food at a time in a specific order to find the problem food(s). This is a very tough diet, but many
individuals are willing to carry this out to get an answer as to whether foods
are the cause of their bowel problems.
This full elimination diet cannot be performed without Dr. Sweet going
over the diet prior to starting to ensure adequate nutrition, AND then
requires continuous follow-up during the entire diet (I usually do this
via email). A full elimination diet
should never be performed without full medical supervision and interpretation
of results.
IT GETS COMPLICATED
The following section outlines other possible
reactions to food. I would like to
stress that this section does not deal with other medical nonfood related bowel
problems such as IBD (inflammatory bowel disease comprising Crohn's
disease, ulcerative colitis, and their variants), bowel cancers, ulcers, and so
on. Most patients I see for possible food allergies have already had an
appropriate work up for other bowel related medical problems (scopes,
ultrasounds, X-rays, etc.). Another way
of looking at this is that individuals often consider the possibility of food
allergy after everything else has been ruled out (and this is certainly
appropriate to make sure you are not dealing with inflammatory bowel disease,
cancer, etc.). The initial portion of
this section deals with IgE mediated food allergy. There are other forms of reactions to foods
both allergic and non-allergic which can cause bowel and systemic
problems. If an individual has chronic
bowel problems (abdominal bloating-swelling, nausea, cramps-pain, vomiting,
diarrhea) that are not caused by IgE mediated allergy they could be caused by
the following:
1-Local Bowel Allergy- In this instance you
have a true IgE mediated allergic reaction to a food, but this reaction is
limited only to the lining of the bowel.
Skin testing is negative for IgE food allergy because this is not a
systemic allergy. There are no IgE
antibodies to the specific food in the rest of that individual (particularly in
the skin) so skin testing is negative.
In most individuals with IgE mediated disease (hayfever, asthma,
anaphylaxis, eczema) the IgE antibody is throughout the body and so skin
testing is positive. This phenomenon of
local IgE allergy exists in the nose and accounts for a significant number of
individuals who have non-allergic rhinitis (i.e. their skin testing is
negative). This is important to know
about as standard allergy medications can be beneficial for these individuals.
2-Other Immune Reactions- There are other
antibodies that can be produced against foods.
In particular IgA and IgG (possibly IgM) antibodies can be directed
against foods. Cell mediated allergy
(delayed allergy) can also occur against various foods. Many medications that are useful for IgE
allergy are not useful here. However,
medications that work against multiple areas in the immune system (steroids,
etc.) and certain anti-inflammatory medications can be helpful.
3-Non-Immune Reactions- These reactions to
foods comprise a huge number of adverse/idiosyncratic reactions. Examples of such reactions would be direct
reactions to chemicals found in foods (i.e. caffeine, tyramine, etc.); the
increase in gas, distention, and loose bowel movements caused by high-fiber in
diets, fatty foods stimulating gallbladder attacks or diarrhea, and so on.
Usually avoidance or a reduction in the amount of these offending foods will
eliminate symptoms. Medication is rarely
required.
4- Lactose Intolerance- A special mention should be made about
lactose intolerance. Lactose is the
natural sugar found in cow’s milk and milk products. Lactose intolerance is an
extremely common condition affecting some children and up to 30% of adults. The
enzyme responsible for handling lactose- “lactase” (splits the lactose molecule
into simple sugars that can be absorbed) in the bowel lining becomes depleted.
When a lactose intolerant individual drinks milk or eats milk products with
lactose in them, lactose is not digested, stays in the bowel, pulls fluid into
the bowel, causing abdominal cramps, bloating, and often loose bowel
movements/diarrhea. This can be diagnosed quite easily at home provided you
keep in mind the reasons for failure that I mentioned above. You should
strictly avoid milk products for 5-7 days. After an avoidance period, on a
Saturday morning (not on a school day or workday) you sit down and over a 1-2
hour period, drink at least half a liter or more of LactaidTM
or LactesseTM milk.
In these milk products the lactose has been pretreated with lactase with the
lactose pretreated. Do not eat or drink anything else. If you have no problems 2 to 3 hours after
this, you are not allergic to milk (because LactaidTM
or LactesseTM contain all the milk proteins that cause true
allergy). The next morning, Sunday, you get up and drink at least half a liter
or more of regular milk. If you have lactose intolerance, you will get
abdominal cramps, bloating, and so on. Lactose intolerance can be treated by
taking LactaidTM tablets-drops,
etc. with milk products and you do not have to avoid milk products. One further
point should be made. Individuals vary tremendously in the severity of their
lactose intolerance, and some require one or two tablets with milk products,
whereas some require considerably more tablets while still experiencing symptoms.
5- Celiac Disease- A special mention also
should be made about “gluten-wheat-gliadin-Coeliac” -
Celiac Disease. This chronic disease is also highly variable in its
presentation. The classical form results in chronic diarrhea and malabsorption.
The non classical forms are much more difficult to diagnose, and some
individuals do not have any symptoms develop for decades. Recent advances in blood tests indicate that
possibly between one and two percent of the population can have this problem,
whether it's symptomatic or not. This is an immune IgA and IgG mediated
disease. The IgA and IgG antibodies are directed against gliadin (a molecule
that is found in wheat, rye, barley). The gold standard for diagnosis is still
the small bowel biopsy done while the individual is actively eating wheat and
related food products, but a blood test is now available that screens quite
accurately for Celiac Disease (patient has to pay for the test). Note; the person must be eating gluten
regularly to be able to diagnose Celiac Disease whether by biopsy or blood
test. Testing cannot be performed –
results are not reliable- if an individual has been strictly avoiding
wheat-gluten. True wheat allergy, IgE
mediated, does exist, but it is much less common (these individuals have a
positive skin test to wheat (i.e. IgE antibody to wheat) and negative testing
for Celiac Disease). Further discussion
of Celiac Disease is not warranted here, but it certainly is a diagnosis I
often consider in certain individuals who feel they may have "food
allergies". There are several good
web sites Re: Celiac Disease and a simple web search will find these.
SUMMARY
Persons suspected of having food allergies, must have their
suspect allergy proven by appropriate tests done or supervised by a
physician experienced in this area. This particular area is frequently
overlooked. Treatment of food allergy revolves around avoidance of that
particular food and any foods that may be contaminated by that food. For severe
food allergy, an epinephrine auto injector (EpipenTM/TwinjectTM) is mandatory.
The individual must know how to use their auto injector and young children
should carry their own on their person as soon as they are capable. Go to the
Contents page and the EpiPenTM-TwinjectTM section for a discussion of this
treatment aspect.
End Dr.
Bruce Sweet 2012