As a GP, you must be aware that people of my generation were fed the myth that a 'healthy diet' was as follows:
Breakfast - cereal with milk followed by toast and jam/marmalade.
Lunch - a sandwich (often white bread with jam/fish paste) rarely with a good protein source.
Dinner - pasta, pizza or curry with white rice.
The 'traditional British' diet of porridge (hard work and only filling for 5 minutes), eggs (loaded with cholesterol), bacon (fat), potatoes (starch), meat (cholesterol again), fish (OK but smelly and too much trouble unless processed in the form of fish fingers/boil in the bag) was absolutely demonised. My mother certainly thought this and was delighted how quickly food could be put on the table.
Over the years, many of these myths have been busted and we are encouraged to eat more protein/fat and complex carbohydrates to fill us up, while cutting down on simple carbohydrates. However, the breakfast cereal myth still persists, driven by the food manufacturers' mantra that children won't eat wholegrain cereals and have to be 'tempted' by sugary children's cereals - otherwise they won't eat breakfast before going to school.
We're getting better about eating fruit and vegetables and cutting back on processed food in general. But sugary cereals? I think some people/children are addicted to the sugar.