Initially I identified it by a blood allergy panel. It came up with
quite a few foods that "tested bad", and for some weeks I was really
good and avoided *all* of them, and felt just phenomenally better.
Then I experimented to see which were making the biggest difference,
and wheat was the way, strong, clear, over-the-top winner, tho milk was
significant too. The others I guess I just wasn't eating enough of or
often enough to make that much difference anyway, and now don't even
remember what they were.
Before that I'd thought I was allergic to any foods, and hadn't noticed
any problem with wheat. That turned out to be simply because I was
eating it multiple times every day and so didn't even know what it
*felt* like not to be in a "wheat haze." Ditto for milk.
What I've learned since, is that if you want to do elimination testing
for allergy, the foods to test first are the ones that you eat every
day, and esp. those about which you feel, e.g., "It's not breakfast
until I've had my __________"--in other words, the ones you're addicted
to! Rude and inconvenient, huh?

having absolutely *none*, you can then eat a meal with LOTS of the
suspect food, maybe even entirely that, a get a very clear view of how
it's affecting you. (And I wonder why one wouldn't just take the easy
way, and if you feel better from *not* eating it, then stop eating it?
:-/ Or go for the drama... ?)
Shannon