It became controversial because Big Food co-opted "balanced diet" in the mid 20th century to demonize animal fat and lionize agricultural fat and sugar. All the

It became controversial because Big Food co-opted "balanced diet" in the mid 20th century to demonize animal fat and lionize agricultural fat and sugar. All the extreme diets you see are a reaction to that. There is absolutely nothing wrong on a dietary level with the majority of "traditional" diets--whether that is the fish, miso, and rice of Japan or the English meat and two veg. The problems come when you get to introduce a million cheap, tasty calories in the form of added fats and sugars.