Myth. Check out the book, "The Low-Carb Fraud" by T. Colin Campbell
He’s a fraud. Been invested in high carb diet for fifty years. Hard to get away from the fact that the natural diet for our species is very very different from what he recommends. Two and a half million years as hunter gatherers is a very stubborn fact. Read books by Boyd Eaton and/or Loren Cordain.
We wrongly took fat out of foods, and replaced it with sugar because food without fat tastes like cardboard. Processed foods contain so much sugar.