So refined carbs are bad due to high glycemic index, too much fat is bad due to seratonin release, is a generally optimal diet then just lean meat and vegetables? We are running out of things to eat...
Lean meat and vegetables seems like a pretty good diet to me! When I'm actually following that, I do need to add some fat, otherwise I'm feeling hungry all the time. Add a bit of fat (olive oil or butter, generally for me) and things are golden. Eggs work too!
lean meat and vegetables (and nuts and fruits) have been the foundation of the human diet for thousands of years.