This code system http://terminology.hl7.org/CodeSystem/diet defines the following codes:

Code	Display	Definition
vegetarian	Vegetarian	Food without meat, poultry or seafood.
dairy-free	Dairy Free	Excludes dairy products.
nut-free	Nut Free	Excludes ingredients containing nuts.
gluten-free	Gluten Free	Excludes ingredients containing gluten.
vegan	Vegan	Food without meat, poultry, seafood, eggs, dairy products and other animal-derived substances.
halal	Halal	Foods that conform to Islamic law.
kosher	Kosher	Foods that conform to Jewish dietary law.