Yes, they're parasites. But some parasites are good, while others not so good.
There are several different types of and also ways to 'acquire' helminths -- some use hookworms that are (I think) in some sort of gel that one puts on one's arm, then covers with a bandage. They then travel to the gut over the period of a month or so (?) and I think then that it takes a few months before people notice a difference.
Here's a google search using the terms 'helminth' and 'food intolerance' for more info:
https://www.google.com/?gws_rd=ssl#q=Helminth+"food+intolerance"
A couple of facebook groups:
https://www.facebook.com/autoimmunetherapies
https://www.facebook.com/groups/htsupport/
There are also studies on helminth therapy for Parkinson's, MS, arthritis, etc., all found with a google search.
But a friend of mine has recommended the HDC helminth, which is microscopic, and just swallowed with a little liquid. She said she's spent over $300,000 during the last 10 years or so trying to help her autistic son, and this has been the most effective treatment so far. His food intolerances almost disappeared within a week, and his anxieties, mood swings, etc., also diminished.
Here's a link to the place she orders them from:
https://biomerestoration.com
They have more info on their hypothesis, especially on the FAQs page, and also there's a link to a youtube video (which is quite long, but interesting -- especially the first 20 minutes or so.)