I can attest to this from personal experience.

After undergoing stomach surgery 8 years ago I started experiencing completely debilitating stomach aches. I had many appointments with my GP and a specialist leading to endoscopies, colonoscopies, CAT scans, and MRI scans all to no avail and they just kept prescribing more and more anti-acids and stronger painkillers.

It was after seven years of this that I paid for a private food allergy test to find that I am allergic to Soya protein. Once I stopped eating anything with Soya in it the symptoms almost completely vanished.

At my next GP appointment I asked why no-one had suggested it could be an allergic reaction only to be told that it is not one of the things they check for or even suggest. My faith in the medical community took a bit of a knock that day.

On a related note, I never knew just how many foods contain Soya flour that you wouldn't expect until I started checking.