Here's a trick from one of my supervisors from school. He's an old school old school old school ND.
Take your resting pulse (find your carotid artery or radial artery and count for 15 seconds and multiply by 4).
Eat a small amount of the food to which you think you might be sensitive. (Make it pure, so if you're testing cheese, just have cheese. Don't wanna confound the experiment!)
Wait 5-10 minutes.
Check your pulse again.
If you're mildly sensitive you'll see a 5-10 bpm increase. If you're seriously sensitive you'll see about a 20 bpm increase. Why? Your body percieves it as a stress, secretes epinephrine, and increases the heart rate.
It's then your perogative whether you choose to continue eating the food.
A little anecdote:
I always use Lent as a spring detox. So this year I gave up wheat, dairy, alcohol, and sugar. My favorite parts of detox are the pre-tox and re-tox. My first re-tox food on Easter Sunday was a Cinna-bon (not sure if you have these where you live, but its basically high sugar, high calorie (800 or so!!!), zero nutritional value, gooey cinnamon goodness and the stores are often located in subway stations, and you can smell them for blocks) that someone happened to bring to my apartment the previous evening. Man oh man! After ingesting part of said gooey cinnamon goodness my resting heart rate went from 78 to 99 bpm!!! My body was freaking out: full on palpitations, shifty vision, sweating.
Crazy stuff eh?