Albert, we attended a GP initially who ordered full blood tests (to determine general health, not iGg antibody testing or anything whacko like that) faecal and urine tests. We've known him for a long time and he's a good diagnostician. When they came back, he ordered further tests on the liver and a mineral count I think it was? We were then referred to another doctor specialising in allergies and they underwent a series of physical tests pertaining to foods.
There were more tests after that and we commenced our regimen.
From a personal point of view, I wasn't surprised to find a sensitivity, was RELIEVED to know it wasn't an allergy but totally dumbfounded at how sugar really has its grip in the most insidious of ways. I am not so quick to dismiss Sarah Wilson (I Quit Sugar) anymore!