How do I know which foods trigger my migraine headaches?

To determine which foods, if any, trigger migraine attacks, keep a diary of what you eat. Depending on how often your attacks occur, you may need to keep the diary for several weeks.

If you're diagnosed with migraine headaches and you feel you're susceptible to food triggers, a registered dietitian can recommend appropriate food substitutes.

If you are uncertain about whether a food triggers a migraine, a food/headache log is your best investigative tool. Depending on how often you get migraines, and how diverse your diet it, you may need to keep this log for 1 to 4 weeks. You should write down:

• everything you eat and drink, including any herbs or supplements you take
• migraine occurrence, including time, duration and severity

Keep in mind, a trigger food may take several hours to cause a reaction. A written log allows you to look back and see if a particular food was eaten before you experience a migraine.

The investigation can be complicated by reaction to food additives. For example, some people suspect MSG causes them problems, but if you list "soup" or "fried rice", you might miss the fact that both these foods contained MSG. If you use many prepared foods, keep the labels. The ingredients' lists can help you sort this out. If you eat restaurant food, many fast food and chain restaurants now have nutrition and ingredients information on their websites.

Another additive suspected of triggering headaches is nitrite, found in many cured and processed meat products. Certain groups of foods contain molecules called amines which may also cause headaches. Examples are aged cheeses, sauerkrauts, cured meats/fish and chocolate.

While some people are sensitive to any amount of a trigger food, others may tolerate small servings. Migraines are only triggered when large amounts of offending foods are eaten at one time. So if you haven't found any one obvious food trigger, look at your whole meal. If you have meals that contain lots of MSG, nitrite or amine foods, you may react to high doses of these.

If you still can't find any clues in your food log, a registered dietitian with expertise in food allergies may be able to analyze it for you.

Numerous studies have shown that the immune system is involved in migraine. Italian researchers found that people with food-induced migraine develop complexes in their blood in which food proteins clump together with antibodies directed against these proteins; these are called circulating immune complexes.

Their appearance is associated with an intricate set of immune responses, which indicate that some type of allergic reaction is taking place.

The significance of understanding that food allergy provokes migraine is the recognition that everyone's "migraine diet" will be different, depending upon which foods they're allergic to.

Many researchers have shown that an allergy blocker called sodium cromoglycate, taken orally before food, can block the induction of food-induced migraine and appears to work by preventing the formation of food-containing circulating immune complexes. This type of allergic reaction cannot be detected by conventional allergy testing, which is based on the presence of a type of antibody called immunoglobulin (Ig)E. IgE antibodies are important for conditions like hay fever, but do not appear to play any role in migraine.

Immunoglobulin (Ig)G food allergy testing is commercially available through many different laboratories in the U.S. It is not a perfect test, but it can help people with migraine headaches and their doctors create an individualized diet that will reduce migraine frequency.

If IgG food testing is not available to you or does not help you to design an effective migraine diet, you can identify food triggers for migraines by using a technique called "elimination and challenge."