How are food allergies diagnosed?

An allergist will perform a physical examination and ask you about your signs and symptoms. You may be asked to keep a food diary and start an elimination diet. In this diet, you are asked to eliminate certain foods from your diet for about two weeks and then reintroduce those foods one at a time to determine which food is the cause of your symptoms. Sometimes, a skin or blood test may be used to diagnose the allergy.

Your doctor may do the following to see which foods are causing your allergies:

• Food Diary: You may need to keep a diary of the foods you have eaten, and any symptoms that followed. Keep this diary especially if you are not sure what food caused the reaction.
• Intradermal/Skin Scratch: Your doctor will mix small amounts of a food with a liquid and then inject the mixture into your arm with a tiny needle. Your doctor will then watch for allergy symptoms.
• Blood Tests: You may need blood taken for tests. The blood can be taken from a vein in your hand, arm or the bend in your elbow. The blood is tested to see how your body is reacting to certain foods.
• Elimination and Challenge: Your doctor may tell you to stop eating certain foods for a specified length of time. These foods will later be added back into your diet, and you will be watched for an allergic reaction.

Many nutritionally oriented physicians perform blood tests to diagnose food allergies. However, in most cases such tests are not really necessary. For patients who have to pay for such tests out of pocket, these tests can be expensive. My experience is that it is best to try a simple elimination diet for seven to 10 days first, to see if your symptoms improve. Start by eliminating the most common allergens:

• Milk and all dairy products
• Wheat (including wheat flour products - e.g., bread, pastries, pasta)
• Corn
• Citrus fruit (e.g., oranges, tangerines, lemons, and grapefruit)
• Peanuts and peanut butter
• Eggs
• Processed foods containing artificial food coloring

As part of an elimination diet, I also recommend using RevitalX - a high-potency multinutrient powdered drink mix from Natural Factors. This product was specifically developed by Michael Lyon, M.D., to be an excellent source of important nutrients to support the gastrointestinal lining and aid detoxification. In an allergy elimination diet, RevitalX is taken twice per day as the primary source of sustenance. RevitalX is mixed with water or juice (fresh vegetable juice is preferred), or it can be blended as a fruit smoothie. Fresh or steamed vegetables and small amounts of fruit can be eaten when you are hungry, and one simple meal is prepared in the evening: steamed vegetables, lean chicken breast, and brown rice (cooked beans, split peas, or lentils along with brown rice can be used as a vegetarian alternative). A lightly sauted stir-fry can also be prepared for this meal.

If your symptoms disappear within seven to 10 days, you're on the right track. By slowly reintroducing the previously avoided foods back into the diet (for example, trying one "new" food every three days), and paying attention to which ones cause symptoms to return, you can identify the real culprit.

Your doctor can perform a skin test to determine which substances cause a reaction. The skin test involves applying a small amount of an allergen (allergy-causing substance) and then making either a tiny scratch or small prick with a needle in your arm or back. The scratches that become red and itchy indicate which substances trigger a defensive response by your immune system.

Your doctor might also do a radioallergosorbent blood test (RAST) to check the number of antibodies produced by the immune system. Elevated levels of certain antibodies can identify particular food allergies. Also, if you maintain a food diary, your doctor will have a much better starting point when determining your allergy-triggering foods.

To diagnose a food allergy, your doctor will start with a medical history and a physical exam. Your doctor may ask:

• What symptoms you have.
• If your family has any food allergies.
• How soon the symptoms begin after eating food.
• If over-the-counter medicines helped.
• If other people also got sick.
• How the food was prepared.
• If you ate any other foods.

It's important to find out whether you have a food allergy or food intolerance. Your doctor may ask you to keep a record of all the foods you eat and any reactions you have to them. Your doctor will also consider if your reaction could have been caused by things like allergies to medicines or insect stings, food poisoning, irritants in foods or exposure to skin irritants.

Your doctor may ask you to try an elimination diet, an oral food allergy challenge or both.

• In an elimination diet, you avoid eating foods that may be causing an allergic reaction and see if your symptoms go away. If symptoms come back when you eat the food again, your doctor can confirm your food allergy. The elimination diet can last from 2 to 8 weeks.
• In an oral food allergy challenge, you eat a variety of foods that may or may not cause an allergic reaction. Your doctor watches to see if and when a reaction occurs. This test is considered the best way to diagnose a food allergy.

After you have been diagnosed with a food allergy, you may also have allergy tests, such as skin tests or blood tests, to find out which foods you are allergic to.