WordNet records no synonym and no antonym for gluten-free diet. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
diet prescribed to treat celiac disease; eliminates such foods as wheat and rye and oats and beans and cabbage and turnips and cucumbers that are rich in gluten
Synonyms, antonyms and the broader and narrower relations for gluten-free diet come from Princeton University’s WordNet. Full sources and licences.