Most breakfast cereals and bread is ultra-processed, doesn't resemble its original food-stuff, is stripped of its original goodness and has a fair amount of sugar added. Wheat, corn etc are also highly highly sprayed crops.
In the case of Cornflakes, however you eat them and whatever you add to them, they are touted as healthy by their makers. It's clever advertising.
I encourage anyone that eats Cornflakes or any of the other similar cereals touted as healthy such as bran flakes, rice crispies etc to take a look at how they are made and what is stripped out/added in. This link gives you an idea;
www.theguardian.com/business/2010/nov/23/food-book-extract-felicity-lawrence
Most bread is the same to a lesser or greater extent. A loaf of white Warburtons toastie loaf/white wraps are much worse on the scale than a loaf of Sainsbury's (for example) wholemeal organic bread for the same reasons. This type of ultra-processed food plays havoc with blood sugars too.
Again, pasta is the same. It's a scale again, white pasta vs say sprouted organic spelt pasta. You get the idea.
It's really hard because like another poster said, we are bombarded with companies telling us how healthy their product is. A lot of us were brought up on convenience food (i was, particularly in the 80s when convenience food really took off) and with our busy lifestyles it's difficult to cook everything from scratch.
I just hope after this situation, more people will move towards eating a less processed diet and we can go back to our ancestral roots a bit more where food is not what i call Frankenstein food. My diet isn't perfect and my kids would live on cheese wraps if they could but we all have a duty to read about/find out what we are putting in our bodies. I hope this helps, I'm not being snippy or nasty about people's diet choices, just want to get more information out about healthy eating. Let's face it, health is everything x