Nutritional Management of Adverse Reactions to Food (Food Allergy)

By Adem Lewis / in , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , /

Adverse reactions to food are either immune
system mediated or not. Immune mediated reactions are the result of the body seeing normal dietary
proteins as being from potential pathogens and reacting accordingly. Thus, a normally
tolerated dietary protein is seen as, say, a potential bacterial or parasitic infection,
and the body mounts a vigorous immune response to fend of the perceived threat of infection.
Signs can vary but gastrointestinal signs like vomiting and diarrhea are common as is
simply reduced appetite. At the same time, cutaneous (or skin) manifestations of an immunological
adverse reaction to food can occur with itchiness and chronic ear infections as common signs.
Itchiness or pruritus may be noticed due to chewing, scratching, and/or licking of the
body. Self trauma due to chewing and scratching can result in secondary infections as bacteria
and fungus are able to infect damaged and often moist skin. Since gastrointestinal (or
GI) and skin signs are not always specific and can have other causes diagnosis can be
difficult. Since immunological adverse reactions to food
can be difficult to distinguish from non-immunological adverse reactions and other diseases with
similar clinical signs, definitive diagnosis is not always made. To definitively diagnose
an immunological adverse reaction to food, an elimination-challenge food trial must be
completed. The elimination portion of the trial is commonly performed with the avoidance
of any previously fed protein-containing foods avoided, but the challenge portion of the
trial, where foods thought to be problematic are refed, is much less commonly conducted.
During an elimination trial, if the patient responds, most folks do not challenge the
pet for fear of the pet becoming ill or itchy once again. Without the challenge, it can
be hard to discriminate if any positive response was actually due to one addressing a non-immunological
adverse reaction to food or not. Specifically, non-immunological adverse reactions can be
due to poor digestibility, lactose intolerance, nutrient deficiency, toxicities (such as histamine
from spoiled tuna or mackerel), and/or idiosyncratic reactions to food additives. As many elimination
trials use more digestible, very high quality foods that avoid common antigens like milk
and are formulated to be complete and balanced with limited ingredients, many of the causes
of non-immunological adverse reactions to food may be concurrently addressed during
an elimination trial resulting in a positive response. Thus, one can only definitively
diagnose an immunological adverse reaction by showing that the refeeding of a particular
food causes the previously seen problems to return. Faced with the possibility of a pet
that is once again vomiting or suffering from diarrhea or itchiness, many people avoid doing
this. Although this is completely understandable, it does prevent one from knowing exactly what
the cause of the problem is. Further complicating the diagnosis is that
some other common diseases like fat intolerance can mimic the gastrointestinal signs seen
with an adverse reaction to food. The practical implications of not definitively diagnosing
the disease means that one may be unnecessarily limiting the foods that can be fed leading
to increasingly reduced food options. Or in the case of fat intolerance ascribing an issue
to a particular food that happens to be higher in fat due to its antigenicity rather than
its fat content, leading to a frustrating cycle of being unable to predict if a food
will be tolerated or not. It is worth mentioning that the elimination trial, when the only
issue is GI signs, can generally be performed much more quickly in days than can a trial
when the issue is skin signs which may take as long as 12 weeks to know if a response
will be seen or not. Also skin signs are often the result of concurrent issues with atopy
or allergies to environmental allergens like pollen or fleas meaning that response may
depend on addressing these other inciting issues as well as any secondary infections
that may have developed due to self trauma. Another challenge with diagnosis can be the
use of blood testing. Blood tests for determining what foods a pet is allergic to are unreliable
and may not be recommended by the very diagnostic lab offering them. A diagnostic that may be
useful in determining possible cause of an adverse reaction to food is GI biospy which
may be of the stomach and duodenum or the colon when performed with an endoscope or
of the GI tract from stomach to colon when taken surgically. Biopsy results showing inflammation
may lead to a diagnosis of inflammatory bowel disease or IBD which may be managed with diet
with or without the addition of immunosuppressive drugs. The main strategy for the nutritional management
of adverse reactions to food is avoidance of dietary proteins that have previously been
fed. These dietary proteins may come from meat/poultry/fish or from plants like grains//fruits/vegetables
including root vegetables. Avoidance may be done as part of the diagnosis in an elimination
trial but may also serve as concurrent therapy. To avoid previously fed antigens, one must
often carefully develop a detailed history of diets or foods fed which is called a “diet
history”. At times, diet histories may be incomplete or the full ingredient list for
previously fed foods may no longer be known. This is typically dealt with by the feeding
of uncommon antigens or protein hydrolysates. “Uncommon antigens” is a preferable phrase
compared to the phrase “novel antigen” as novelty is defined by the particular pet not
the food. How common an ingredient is in pet food is related in part to geography. For
example, in the US kangaroo meat may be uncommonly fed to pets but not in Australia. Thus, kangaroo
meat may be novel or new to more pets and less common in the US compared to Australia,
but one cannot determine if kangaroo is novel for a particular pet without a diet history.
If a diet history is unknown, using an uncommon antigen can decrease the likelihood of the
pet having been fed it previously, and thus, having developed an immune response, but this
approach is not perfect. Instead of feeding an uncommon antigen diet
when the full diet history is unknown, hydrolyzed protein-based diets may be fed. Hydrolyzed
proteins are proteins that have been broken into small pieces at the molecular level.
The hope is that the small pieces of protein that result will be too small to be “seen”
by the immune system. Since these pieces are so small they hold the hope that the body
will be unable to make antibodies to them given their small size. Since theoretically
the body cannot make antibodies to these hydrolyzed proteins, they are the only protein source
that can be correctly referred to as being potentially “hypoallergenic”. Unfortunately,
the hydrolysis process is not a perfect one, and it is possible for some intact protein
to remain that could be reacted to by the immune system. Another challenge with avoiding previously
fed antigens is the potential for cross-reactivity and hidden antigens. Cross-reactivity refers
to the potential for a closely related food that a pet has been fed and developed an immune
response to causing a reaction to a food that has never been fed before. For example, there
is evidence that beef and lamb could result in a cross-reaction. Unfortunately there is
no clear list of cross reactive foods. Hidden antigens are most commonly hiding in plain
sight in the form of flavorings used in chewable medications like flea or heartworm preventative
or arthritis medications. In addition, flavorings or palatants may be used on some pet foods,
which raises a concern of possible antigenicity especially since these flavorings are commonly
made from more common meats/poultry. Finally diets for the nutritional management of adverse
reactions to food are usually limited in the number of ingredients used to reduce the likelihood
of a non-tolerated food being fed as well as to reduce the risk that an adverse reaction
to multiple foods developing simultaneously. Lowering of the omega-6 to long-chain omega-3
fatty acid ratio can be potentially helpful in the nutritional management of adverse reactions
to food. During any inflammatory process, the body’s immune cells make eicosanoids which
are signaling molecules. Eicosanoids can be made from omega-6 or long-chain omega-3 fatty
acids. Eicosanoids made from omega-6 fatty acids are better at signalling. This means
that eicosanoids made from omega-3 fatty acids are not as effective at signalling and as
a consequence consumption of foods rich in long-chain omega-3 fatty acids can actually
reduce inflammation. This reduction in inflammation can decrease the overzealous reaction of the
body to dietary proteins and potentially reduce the potential for an over-reaction to newly
introduced dietary proteins. Although shorter chain omega-3 fatty acids, like alpha-linolenic
acid that comes from terrestrial plants, can be elongated to the long-chain omega-3 fatty
acids, EPA and DHA, their conversion is poor. Thus, the common use of marine oils and/or
fish to enrich foods with these “less inflammatory” fatty acids. At times a concern is raised
about the antigenicity of these oils, but some products are distilled reducing the likelihood
of this as can the use of oils or fatty acids from fish species or algae that are not as
commonly used in pet food. Ratios can be variable depending on what specific fatty acids are
included in the calculation, but one often looks for Linoleic Acid + Arachidonic Acid
: EPA + DHA ratios of less than 5. Special fats and/or oils are added to diets
to provide long-chain omega-3 fatty acids. At the same time, there can be instances where
concurrent dietary fat restriction may be indicated. This is not common but diseases
like lymphangiectasia or concurrent pancreatitis may result in the need to lower the amount
of fat in the overall diet. Generally, normal to slightly higher levels of dietary fat,
which generally increases palatability, digestibility, and energy density, may be fed unless a disease
treated with fat restriction is already identified. If the normal or higher dietary fat level
is not tolerated, a decrease in dietary fat may be tried. Dietary fiber is usually categorized as being
soluble or insoluble as well as being fermentable or nonfermentable. Generally soluble fiber
is also more likely to be fermentable. This means that fiber that “holds” water can be
used as an energy source for bacteria in the GI tract. Insoluble fiber that adds bulk,
but without holding water, is generally also not useful to gut flora. A newer term that
is applied to fermentable fiber is prebiotic. Prebiotics should promote a more healthful
GI flora. Most naturally occurring fibers are a mixture of fiber types. At the same
time, too little fiber as well as too much fiber can cause GI distress. Consequently
some pets benefit from very low dietary fiber while others benefit from more. Thus, lower
or higher fiber diets may be tried and additional fiber of different types may added or removed
depending on response with a special focus on stool quality. Adverse reactions to food requires a lifelong
awareness of exactly what is being fed to a pet to avoid offending antigens. Care must
be taken to watch for the development of new reactions as pets prone to adverse reactions
to food can develop new reactions in as little as two weeks. The recurrence of a reaction
may initially be mild with a reluctance to eat a previously enjoyed and readily consumed
food. A return of itchiness is also possible with skin signs, but may not be as readily
apparent or as quick to reappear. The development of an adverse reaction to food in a younger
pet may warrant more aggressive dietary challenge to hopefully avoid eliminating foods that
might actually be tolerated. Without conducting challenges, one might develop such a severely
restricted list of believed to be tolerated foods that no commercially prepared option
is available. Fortunately, with the right care pets with adverse reactions to food can
often return to a normal and long life.

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