Food allergiesPeople are most often allergic to the foods the like to eat the most. This is because we expose our immune system to these foods all the time. Food allergies can affect any part of the body, including the brain.
The most common food allergies are:
Testing for food allergies
IgE allergy tests:
This is a type of allergy test traditionally run by medical doctors. And IgE allergy is one which causes immediate symptoms. Some people just have genetic IgE allergies to foods and these need to be avoided. However, most allergic responses to foods are not IgE.
IgG food allergies:
This is test more commonly run by alternative doctors. This is looking for another type of antibody which causes a delay reaction. Often people eat an offending food, but don't get a reaction until a couple of days later. IgG allergies are generally not genetic, but developed over time as we expose the immune system to the same allergens over and over again. Often people with many IgG allergies really have digestive problems and something called "leaky gut."
More about "leaky gut" can be found on this web site's page on autoimmune thyroid disease.
There are blood tests for IgG allergies. They are very controversial, sometimes they show what the food allergy is, sometimes not. Often they will report false positives. Although there are many good practitioners who do use these tests, I generally do not.
Some problems with IgG food allergy panels are:
- They are unreliable with many false positives and negatives - and so are very controversial within the natural health field.
- High cost. If finances are limited I think other tests (especially digestive tests, which cost a lot less) are better since they help show the cause of food allergies.
- Often the results are to not eat wheat, dairy, soy, corn and eggs. No one needs to spend a few hundred dollars on a food allergy test to find out those are our most allergenic foods.
However, this does not mean IgG panels don't have their place. As with other functional lab test, they are best used when appropriate.
Alcat blood test
The Alcat allergy test is an alternative way to test for food allergies that does not have some of the problems associated with IgE and IgG testing.
Celiac and gluten sensitivity
Celiac disease is a disorder where the immune system over reacts to a protein in wheat (gluten) and causes tissue damage. Although classically regarded as a gastrointestinal disease we now know that celiac disease can affect almost every organ system. Celiac disease has been associated with dementia, Alzheimer's and other mental symptoms. 
Celiac disease is just one possible presentation of gluten sensitivity. It's very possible to be gluten intolerant, yet not be celiac.
Historically gluten sensitivity has been treated under the assumption that only the grains wheat, barley, rye, spelt and oats can trigger a reaction. This assumption may be premature as all grains contain gliadins and the proof that these other grains are safe to eat is lacking.
There are numerous tests available which related to gluten sensitivity. On blood tests doctors may or endomysial and trans-glutaminase antibodies. The problem with these tests is the chance for false negatives. Tests should be used to confirm gluten sensitivity, but not necessarily to rule it out.
Genetic testing is available for gluten sensitivity however, which bypasses some of the problems with antibody tests.
Celiac.com is also an excellent source for more information.
 "Celiac Disease Linked to Dementia." WebMD - Better Information. Better Health. Web. 05 Feb. 2011. <http://www.webmd.com/digestive-disorders/celiac-disease/news/20061013/celiac-disease-linked-dementia>.