You already have a policy
Find the actual food wording and endorsements. Ask how the existing diagnosis and recommended product will be assessed under that form.
You are shopping after the diet was recommended
Investigate pre-existing-condition treatment before buying for this expense. A food benefit in a new policy may not apply to an already documented problem.
Your policy excludes food
Keep the food in the care budget. Ask about associated examinations, testing or medication separately; excluding food does not answer every other line item.
As current examples of differing treatment, ASPCA Pet Health Insurance’s Complete Coverage materials include prescription food for covered conditions, with general maintenance and weight-management uses excluded. Neither statement replaces the form that applies to your pet.