Put the diet in writing before the first meal
A spoken explanation on day one rarely survives contact with a busy kitchen. Write down exactly which foods, ingredients and preparation methods are excluded, and which are borderline and need a check before use (fish sauce, gelatin, certain stocks, lard in pastry). Include a short list of approved substitutes so a missing ingredient has an obvious answer instead of an improvised one.
If the diet is medically necessary rather than a preference, say so and explain what happens if it's not followed, so the instruction is treated with the right weight.
- List excluded foods and hidden ingredients to check
- Note borderline items that need confirmation before use
- Give approved substitutes for common recipes
- State whether the diet is medical or a household preference
Agree how strict cross-contact needs to be
Vegetarian and special-diet households vary widely on this point, and assuming agreement is where most misunderstandings start. Some families are comfortable if the meal itself contains no restricted ingredient; others need separate chopping boards, pans or oil so nothing crosses over from other cooking. Decide which applies to your household and say so plainly, rather than leaving it to be inferred.
Where only one household member follows the diet, agree a workable system for shared equipment: which pots are diet-only, how oil is stored, and what happens with leftovers, so the arrangement doesn't quietly erode after the first few weeks.
Check the pattern early, not after months
Review a handful of actual meals in the first two weeks rather than assuming the written list has been fully understood. This is also the point to correct small misreadings, such as a substitute ingredient used inconsistently or a borderline item treated as approved by default.
If mistakes keep recurring after a clear written brief and an early check-in, treat it as a conversation to have directly rather than a problem to work around indefinitely.