The low-carb flu is real and it’s terrible. While it doesn’t kill as many as the Spanish flu of 1918 did or inspire the amount of panic seen during the 2009 swine flu epidemic, low-carb flu has dissuaded millions of people from pursuing and sticking to a healthy diet. You can laugh now that you’re fat-adapted and humming along on stored body fat, but you’ve forgotten just how terrible the transition from sugar-burning to fat-burning can be. Do any of the following symptoms sound familiar?