TYPES OF REACTIONS TO FOOD                                                         

Not all reactions to foods are due to allergic reactions.  

Food allergies can result in:

1. Food anaphylaxis (rare) where hives, throat swelling, asthma, severe indigestion, low blood pressure occur from food allergies moments after ingestion (< 2% of patients) 
2. Much more common are “cross reactive food allergies” also called “oral allergy syndrome”.  Here small amounts of allergenic food (often fruits and vegetables) may be well tolerated, but large amounts cause tongue itching or tingling, indigestion, bloating or diarrhea.  Up to 90% of allergic patients may have some of these indigestion reactions with certain fruits and vegetables (melons, corn, wheat, soy, celery, garlic, avocado are typical triggers).
3. Adverse reactions due to chemicals occurring in the food (e.g., coffee, alcoholic beverages, NutraSweet, sugar (hyperglycemia)).
4. Adverse reactions due to bacterial contaminants in the food (e.g., food poisoning, E.coli from undercooked meat, travelers’ diarrhea in Mexico).
5. Adverse reactions to certain food preservatives due to a special sensitivity, usually of unknown cause, found in a small number of people (e.g., “Chinese restaurant syndrome”/MSG intolerance).
6. Inability to digest the food properly due to a defect in the patient’s digestive system (e.g., lactase deficiency/lactose intolerance, (try Lact-Aid), bean indigestion, (try Bean-o).

TIMING OF ALLERGIC REACTIONS TO FOODS 

1. Severe allergic (anaphylactic) reactions to food tend to occur rapidly after eating the food, often immediately during the process of eating the food or within a few minutes.  It is not uncommon for food allergies to cause itchy lips, swollen tongue and a lump in the throat shortly after eating the food.
2. If anaphylactic symptoms occur later than 4 hours (some experts feel that the upper limit is only 2 hours) after eating a particular food, then that food is usually not the cause of the symptoms.
3. However, indigestion, bloating, gas and diarrhea (gastrointestinal symptoms) can commonly occur 4-12 hours (up to 24 hours) after eating allergenic foods.  See “cross reactive food allergy” discussion above.

SYMPTOMS CAUSED BY FOOD ALLERGIES

1. The symptoms caused by food anaphylaxis are similar to the symptoms caused by other allergic reactions.  The main symptoms are itching and hives/swelling.  When the swelling occurs in the vocal cords it can cause hoarseness and when the swelling is in the stomach and intestines it can cause vomiting, abdominal cramps and diarrhea.
2. Food cross-reactive allergies generally do not cause or aggravate asthma or nasal symptoms.  Nasal and chest symptoms much more likely are caused by dusts and inhaled allergens which impact directly into nose and lungs. When foods trigger nasal & chest symptoms, this indicates a more severe allergic reaction involving your entire body (technically called “systemic anaphylaxis”).  During these “systemic” reactions there is often allergic involvement of not only the nose and lungs, but also the eyes, throat, vocal cords, digestive tract, skin, blood vessels, etc.
3. Food allergies generally do not cause behavioral changes such as hyperactivity, mood changes, poor concentration, etc.  If food protein were bothering the brain, it would also circulate through the rest of your body and typically cause a constellation of other allergy symptoms described above under “systemic reactions”.      

INVESTIGATION OF FOOD ALLERGIES ​​​​​​​

1. Your history must be carefully documented to see if food allergies are present, and to determine, which foods are possible offenders.  Then skin tests to suspected foods are performed.  The skin tests are generally very reliable in demonstrating whether or not you have allergic IGE antibodies to these foods.  If the skin test to a particular food is positive, and the food is poorly tolerated by history causing symptoms each and every time food is ingested, then it is likely that food is a culprit and should be avoided.  If the apparent offending food can be avoided, this is the best approach.  But if the food is a key part of the diet, a food challenge may be needed. 
2. Other foods that could provoke a positive skin test (or RAST test) may be perfectly well tolerated since stomach acid and enzymes regularly digest foods into harmless components.  Therefore, any food that is well tolerated by a patient should be safe to eat regularly regardless of skin test results. 

TREATMENT OF FOOD ALLERGIES

1. Food cross reactivities causing oral or GI (gastrointestinal) symptoms are common.  Avoid large amounts of any foods causing repeated mouth itching, indigestion, or bloating etc.  Small amounts and foods used in cooking are usually well tolerated.
2. Once a food has been implicated as a cause of food anaphylaxis (by history of repeated reactions and positive skin tests), the only acceptable treatment is avoidance.  There is no treatment available which will allow a person with food allergies to eat the offending foods without causing risk of an allergic reaction.
3. In cases where the foods to which you are allergic are commonly mixed as ingredients in the preparation of other foods (e.g., peanuts, milk, soy), then it is recommended that food anaphylaxis patients carry 2 Epi-Pens (adrenalin auto-injector) and Benadryl (25mg.) for immediate use in case you accidently consume an allergenic food.  Use 2-4 Benadryl immediately if you realize you consumed an food.  If any signs of serious allergic reaction occur, then immediately take an Epi-Pen dose and go to the nearest emergency room or your doctor’s office.  While on the way to the emergency room, if your symptoms continue to get worse, then take the second Epi-Pen dose.