December 15, 2011

Allergies, Sensitivities, and Intolerance

In the last post i talked about the association between a leaky-gut and a leaky-brain, and that the nexus is inflammation.   Inflammation, again, is part of an allergic reaction, which is narrowly defined as symptoms following a histamine response.

Since we have been focusing on food, nutrition, and gut health, i wanted to spend a few moments clarifying food allergies,  which are becoming a major concern in our society, so much so that peanuts are now banned in public schools. in fact, the incidence of food allergies has increased by 8% from 1997-2007 in children under 18 years of age.  There are many theories as to why food problems are on the rise, from our overly hygienic society to the surreptitious use of GMOs (genetically modified organisms), but that is for a later posting.

For simplicity, there are 3 main problematic, biologic reactions to food:  intolerance, sensitivities, and allergies.

A food intolerance is not an allergic reaction, per se, as it is not mediated by an allergic response.  For that reason, it is also referred to as a non-allergic food hypersensitivity.  Intolerance is a digestive system response.  The most common intolerance is lactose intolerance, effecting roughly 1 in 10 people worldwide. With this problem, intestinal villi are lacking the lactase enzyme to breakdown lactose.  The milk sugar then typically causes GI dystress.  Although food intolerance can sometimes cause headaches and nervousness, the symptoms tend to be bound to the GI system with diarrhea and bloating.

Food allergies and sensitivities, on the other hand, are mediated by your body’s immune system.  Allergies and sensitivities can be divided into acute and delayed reactions, respectively.  Acute reactions are mediated by IgE (and IgG) food-specific antibodies, causing an immediate histamine response.  These are the reactions that lead to throat swelling anaphylaxis with peanut exposure, for instance.  These type I responses are activate mast cells, B Cells, and Eosinophils.  Symptoms include itching, swelling, flushing, and smooth muscle contraction, leading to edema, atopic dermatitis, GI symptoms and anaphylaxis (airway swelling shut).

Sensitivities, on the other hand,  involve food-specific immunoglobulin molecules that form food-immune complexes which can then stimulate the complement cascade reaction and local inflammation. The complexes can deposit in body tissues, resulting in further inflammation and potentially triggering autoimmune responses.  There type III reactions are mediated by the IgG immunoglobulins, of which there are 4 subclasses, with  IgG1 and IgG4 being the most prevalent in food sensitivity reactions.  Unlike the immediacy of true food allergies, sensitivities are delayed from a few hours to up to 7 days post-consumption, making it truly difficult to trace the causal relationship between the trigger and the symptom.  Typical symptoms of food sensitivities can be bloating, sluggishness after eating, GI sytmpoms, dark circles under the eyes, and chronic congestion, though as has been indicated previously, these reactions can also cause myriad psychiatric conditions.

Unfortunately, laboratory testing is controversial and not very accurate when it comes to food sensitivities.  I have heard anecdotes of a physician sending off two specimens of his own blood taken at 2 different times in the same day yielding entirely different allergy profiles.    The only real test is through an elimination diet, generally requiring the removal of the suspected offending food for approximately 1 month, and then the slow re-introduction or re-challenge to see about subsequent symptom development.

Because food sensitivities and the subsequent allergic reactions can, in theory, be contributing factors in almost all psychiatric conditions, one must constantly be thinking about the role of diet in hearing a patient’s anamnesis, with strongly consideration for an elimination diet as part of the care plan.