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Few areas cause our patients more confusion than a food allergy, food intolerance and what this has to do with their digestive problems. Wherever you turn, there seems to be conflicting information; and your friends, relatives and lots of total strangers are happy to give you their opinions also.

Some definitions pertaining to these conditions include:

Allergy: The body's immune system normally reacts to the presence of toxins, bacteria or viruses by producing a chemical reaction to fight these invaders. However, sometimes the immune system reacts to ordinarily benign substances such as food (example: peanut allergy) or pollen, to which it has become sensitive. This overreaction can cause symptoms from the mild (hives) to the severe (anaphylactic shock) upon subsequent exposure to the substance. An actual food allergy, as opposed to simple intolerance due to the lack of digesting enzymes, is indicated by the production of antibodies to the food allergen, and by the release of histamines and other chemicals into the blood.

Intolerance: Food intolerance is a digestive system response rather than an immune system response. It occurs when something in a food irritates a person's digestive system or when a person is unable to properly digest or breakdown, the food. Intolerance to lactose, which is found in milk and other dairy products, is the most common food intolerance, with gas, bloat and/or diarrhea typical symptoms.

Dietitian: A trained licensed professional who is best source of detailed dietary advice when medical conditions warrant it. They must have at least bachelor’s degree & internship, continuing education.

Allergist: An MD or DO who specializes in immunology and allergy. If you have true food allergies or clear immune reactions to food, an allergist can help guide specialized testing and treatment.

Nutritionist: Anyone who advertises themselves as such. Some have very sound nutrition education and training, college degrees in nutritional sciences, for example. Others are self-taught and not had their knowledge verified by anyone! Naturopaths (alternative medicine practitioners who promote ‘holistic’ practices) often “prescribe” nutritional treatments; these individuals do have some required training and licensing in California but medical training is quite limited and qualifications vary widely. Be skeptical of “nutritionists” until you check out their training, qualifications!

Food Intolerance Overview

There are many factors that may contribute to food intolerance. In some cases, as with lactose intolerance, the person lacks the chemicals, called enzymes, necessary to properly digest certain proteins found in food. Also common are intolerances to some chemical ingredients added to food to provide color, enhance taste, and protect against the growth of bacteria. These ingredients include various dyes and mono-sodium glutamate (MSG), a flavor enhancer.

Substances called sulfites are also a source of intolerance for some people. They may occur naturally, as in red wines or may be added to prevent the growth of mold. These cause asthma attacks in some.

Salicylates are a group of plant chemicals found naturally in many fruits, vegetables, nuts, coffee, juices, beer, and wine. Aspirin also is a compound of the salicylate family. Foods containing salicylates may trigger allergy symptoms in people who are sensitive to aspirin. Of course, any food consumed in excessive quantities can cause digestive symptoms. Pepto Bismol contains a form of salicylate.

How can you tell the difference between a food allergy and intolerance?

Food allergies can be triggered by even a small amount of the food and occur every time the food is consumed. People with food allergies are generally advised to avoid the offending foods completely. On the other hand, food intolerances often are dose-related. People with food intolerance may not have symptoms unless they eat a large portion of the food or eat the food frequently. For example, a person with lactose intolerance may be able to drink milk in coffee or a single glass of milk, but becomes sick if he or she drinks several glasses of milk. Allergy to actual milk protein is rare in adults; kids with this outgrow it early.

Food allergies and intolerances also are different from food poisoning, which generally results from spoiled or tainted food and affects more than one person eating the food.


Most food intolerances are found through trial and error to determine which food or foods cause symptoms. You may be asked to keep a food diary to record what you eat and when you get symptoms, and then look for common factors. Another way to identify problem foods is to go on an elimination diet. This involves completely eliminating any suspect foods from your diet until you are symptom-free. You then begin to reintroduce the foods, one at a time. This can help you pinpoint which foods cause symptoms. Don’t do elimination diets on your own! Get advice from physician or dietitian and monitor results with a professional only. Unwise elimination leads to compromised nutrition and a poorer quality of life.


Treatment for food intolerance is based on avoiding or reducing your intake of problem foods and treating symptoms when they arise. Small exposures are usually not a problem.


Taking a few simple steps can help you prevent the symptoms associated with food intolerance.

Learn which foods in which amounts cause you to have symptoms and limit your intake to amounts you can handle. When you dine out, ask your server about how your meal will be prepared. Some meals may contain foods you cannot tolerate and that may not be evident from the description on the menu. Learn to read food labels and check the ingredients for problem foods. Don't forget to check condiments and seasonings. They may contain MSG or another additive that can lead to symptoms.

Reading Food Labels

Food labels are required to list whether they contain even traces of any of the MOST COMMON foods that can cause serious allergic reactions. If you are allergic to something else, you’ll need to routinely look through the entire food label and recognize terms similar but not the same as what you react to—and avoid the product. Many smart companies now indicate if their food might have been prepared on equipment that also is used for foods with the major allergens, e.g. nuts.

Food Allergies Overview

A food allergy is an exaggerated immune response triggered by eggs, peanuts, milk, or some other specific food. Eight foods account for 90% of all food-allergic reactions. They are milk, egg, peanut, tree nuts, fish, shellfish, wheat, and soy. Food labels MUST list whether a food contains any of these!


Normally, your body's immune system defends against potentially harmful substances, such as bacteria, viruses, and toxins. In some people, a substance that is generally harmless, such as a specific food, triggers an immune response. The cause of food allergies is related to your body making a type of allergy-producing substance called immunoglobulin E (IgE) antibodies to a particular food. Although many people have a food intolerance, food allergies are much less common (perhaps 2% of adults; most childhood allergies are outgrown by age 4-6!!). In a true food allergy, the immune system produces antibodies and histamine in response to the specific food. Any food can cause an allergic reaction, but a few foods are the main culprits. In children, the most common food allergies are to Eggs, Milk, Peanuts, Shellfish (shrimp, crab, lobster, snails, clams), Soy, Tree nuts, Wheat. Allergies to peanuts, tree nuts, and shellfish tend to be lifelong. In older children and adults, the most common food allergies are: Fish, Peanuts, Shellfish, Tree nuts, Food additives -- such as dyes, thickeners, and preservatives – may rarely cause an allergic or intolerance reaction.

An oral allergy syndrome may occur after eating certain fresh fruits and vegetables. The allergens in these foods are similar to certain pollens. Examples are ragweed pollen/apple; tree (birch, others) pollen/apple, pear, carrot, celery; mugwort pollen/celery, some spices; grass pollen/fig, tomato, melon. Digestive or lung symptoms are rare.

Latex-food allergy syndrome: about half of people with latex allergy may react to banana, avocado, chestnut, and kiwi; and get an itch, eczema rash, mouth-face swelling, asthma reaction, GI upset, and anaphylaxis. Many Americans believe they have food allergies, while in reality, fewer than 1% have true allergies. Most people's symptoms are caused by intolerances to foods such as Corn products, Cow's milk, and dairy products (See: Lactose intolerance), Wheat and other gluten-containing grains (See: Celiac disease)


Symptoms usually begin immediately, within 2 hours after eating. Rarely, the symptoms may begin hours after eating the offending food. Key symptoms include hives, hoarse voice, and wheezing.

Other symptoms that may occur include:

  • Abdominal pain/cramps often with vomiting and/or diarrhea
  • Diarrhea usually with stomach cramps
  • Difficulty swallowing
  • Itching of the mouth, throat, eyes, skin, or any area (oral allergy involves itchy lips, tongue, throat and sometimes swollen lips, without other reactions).
  • Light-headedness or fainting
  • Nasal congestion
  • Runny nose
  • Swelling (angioedema), especially of the eyelids, face, lips, and tongue
  • Shortness of breath


Avoiding the offending foods may be easy if the food is uncommon or easily identified. However, you may need to severely restrict your diet, carefully read all package ingredients, and ask detailed questions when eating away from home.


Some complications include:

Anaphylaxis is a severe, whole-body allergic reaction that is life-threatening. Although people with oral allergy syndrome rarely have an anaphylactic reaction, they should ask their doctor whether they need to carry injectable epinephrine.
Food allergies can trigger or worsen asthma, eczema, or other disorders.

Tests and Diagnosis

In severe reactions, you may have low blood pressure and blocked airways. A blood or skin test can be done to identify elevated antibody levels (particularly IgE) and confirm that you have an allergy. With elimination diets, you avoid the suspected food until your symptoms disappear. Then the foods are reintroduced to see if you develop an allergic reaction. In provocation (challenge) testing, you are exposed to a suspected allergen under controlled circumstances. This may be done in the diet or by breathing in the suspected allergen. This type of test may provoke severe allergic reactions. Only a doctor should do the challenge testing. Never try to deliberately cause a reaction or reintroduce a food on your own. These tests should only be performed under the guidance of a health care provider -- especially if your first reaction was severe.
There are three common types of allergy testing: skin prick test, blood test, and food challenges. An allergist can perform these tests, and they can also go into further depth depending on the results.

Skin testing on the arm is not as effective as other tests. For skin prick tests, a tiny board with protruding needles is used. This test only works for IgE antibodies. Allergic reactions caused by other antibodies cannot be detected through skin prick tests. Blood testing is another way to test for allergies, but it only detects IgE allergens and does not work for every possible allergen. RAST, Radio-Allergo-Sorbent Test, is used to detect IgE antibodies present to a certain allergen. The score taken from the RAST test is compared to predictive values, taken from a specific type of RAST test. If the score is higher than the predictive values, there is a great chance the allergy is present in the person. One advantage of this test is that it can test many allergens at one time.[29]. It isn’t uncommon that RAST tests don’t correlate well with actual reactions to food!!

Food challenges test for allergens other than those caused by IgE allergens. The allergen is given to the person in the form of a pill, so the person can ingest the allergen directly. The person is watched for signs and symptoms. The problem with food challenges is that they must be performed in the hospital under careful watch, due to the possibility of anaphylaxis. It can be highly subjective or biased.

The best method for diagnosing true food allergy is to be assessed by an allergist.

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