Iirc, I once read that Queen Elizabeth eats 4 small meals a day, and quite often cooking shows will mention if something has been known to be a favourite of a royal, and generally it’s quite traditional food. Meat, veg, salad, pastry, bread, etc.
(I think I remember she has afternoon tea at 5pm (tea w/ jam & cream scones), potted prawns being one of her favourites, and that she loves chocolate.)
They do live a long time don’t they!
Apparently modern British Royals live an average of 30 years longer than us peasants!