" However, if they become too high, taking a dose of medication will bring it back down. I consider the optimal blood sugar range while fasting to be 8.0 to 10.0 mmol/L, if you are taking medication. This range is higher than the nonfasting norm, but the mildly elevated levels are not harmful in the short term while we are attempting to improve the diabetes, and the primary goal while "

― Jason Fung , The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting