Just thought I would note that I went out for a 20+ mile group cycle ride on Saturday fuelled by my morning butter+cream+coffee and just had a black coffee at our rest stop (rent, really for the use of the table) whilst the rest tucked into cakes and stuff. Still going strong at the end. So I conclude that I must be running on fats for energy. I note that keto-adapted athletes often don't show ketones in their blood once they are fully adapted. I do, but then again I wouldn't class myself as an athlete. I'm still trying to get my head round how your body signals an energy deficit if you are fat fuelled (as you don't hit the wall a couple of hours in) and also why you feel physically tired the next day. Is this just your body being slow to clear metabolic wastes from your exercise? Once more unto the Volek & Phinney, dear friends!