Readers know that my idea of a healthy breakfast is two coffees and sometimes a little nicotine. For adults, the idea that "breakfast is the most important meal of the day" was debunked long ago. Growing kids, of course, need food all the time including protein at breakfast.
If you do heavy labor all day, it's another matter. All I do is to work out at the gym for an hour or so every morning, and some yard work on weekends (as little as possible because I have become bored with it), and take good walks on weekends. That is sedentary.
Sometimes, though, there are occasions for a hearty breakfast.
I have always liked kippers with some eggs. In Scotland, the kippers are about a foot long. Too much. The canned kippers that you find in US supermarkets are barely OK.
Another breakfast that some hate but I love: Creamed Chipped Beef on Toast (aka shit on a shingle). A classic prep school, and military, breakfast.
Moving a bit south in the USA, there's Shrimp and Grits. Delicious.
And the ultimate American breakfast (South and Midwest especially): Biscuits and Gravy. Every family has its own recipe, so I won't link one. Those Bob Evans restaurants make a fine one, but I don't think they let you in unless you weigh over 250 pounds. Grits on the side are good.
To stay multicultural, I can't omit the English Breakfast. Blood sausage: