Five Tools for Diagnosing Food Intolerances

Not all adverse reactions to food are true allergies — that is, IgE-mediated reactions in the immune system. Some are considered food intolerances or sensitivities.

Because food intolerances can be triggered by a number of causes, making the diagnosis is somewhat difficult; tests for several common food intolerances are specific to those disorders.

However, there are a few tests and techniques that you're likely to encounter when your doctor, allergist, or gastroenterologist is diagnosing food-related symptoms that don't appear to be true allergies.

Keeping a Food Diary

woman writing in journal at kitchen table
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If your doctor is not sure whether food is the cause of your symptoms, or if your doctor would simply like to look for patterns in what you've been eating when your symptoms occur, she may recommend that you keep a food diary or food journal.

This should be a complete record of the foods you've eaten over a given period of time (usually at least a week), plus a record of any symptoms you suffer during that time. A food diary often is combined with other diagnostic methods.

Food diaries may be used to narrow down potential migraine triggers or to assist training athletes in addition to their use in diagnosing food intolerances.

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Elimination Diets

While different doctors prefer to conduct them in different ways, the basics of all elimination diets are similar: drop the foods you suspect may be causing you problems, and then see what happens when you reintroduce them.

You either can cut out the foods that are most likely to be causing you problems, or pare your diet down to all but a few foods that most likely are not causing your symptoms. Once you've stabilized on your new diet, you then can slowly increase the number of foods you eat. You do this while tracking your symptoms.

Elimination diets can be used to assess a variety of food intolerance symptoms.

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Blood Tests

Most diagnostic blood tests for food intolerances are considered controversial. However, there is one condition where blood tests should be the first step in diagnosis: celiac disease.

Celiac disease isn't really a food intolerance; it's actually an autoimmune condition. When you have celiac disease and consume the protein gluten (found in the common grains wheat, barley and rye), your immune system reacts by attacking your small intestine.

Blood tests can detect the antibodies generated in this immune system attack, which is why they're useful in screening for celiac disease. However, these tests do carry some risk of false positives (that is, a result indicating celiac disease even though the patient doesn't have celiac disease) and false negatives, and so they usually are followed by an endoscopy.

Blood tests may also be used to screen for lactose intolerance.

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Endoscopy (Small Bowel Biopsy)

An endoscopy is an examination and biopsy of the tissue of the small intestine, often used to test for celiac disease (as well as several other non-food-related conditions).

In this test, a flexible tube with a camera attached is lowered into the stomach, usually through your esophagus. When checking for celiac disease, gastroenterologists look for patterns of damage to the intestinal lining.

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Breath Tests

A test that measures the concentration of hydrogen in the breath is another method sometimes used to test for lactose intolerance. Hydrogen is a byproduct of lactose consumption in people with lactose intolerance.

This test involves taking a baseline sample of the patient's breath, then taking samples over several hours after the patient consumes lactose to see if the concentration rises sharply.

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