16 hours into my 20 hr fast. Glucose is 107. Seems like my body is producing a good amount of sugar without any food at all.
May be glycogenolysis (glycogen -> glucose) and/or gluconeogenesis (protein / fat -> glucose) at this point. The former can supply up to a few thousand calories, the latter keeps going so long as one has tissue to spare, but takes a dip under extended fasting conditions (> ~48 hours), as ketone production and utilization progressively increases. Together they ensure that there’s always adequate glucose supply for those cells that don’t fancy a high-fat diet (lack mitochondria).