Blood glucose levels are for sure a funny thing.
If you have been on a true keto diet and in ketosis for longer than 3-4 months, your fasting BG can start to rise to 100-110.
Your reaction to a high carb meal can send your BG to over 160 for I believe everyone diabetic or not.
It's all about "physiologic glucose sparing" Your muscle refuse glucose causing your blood glucose to rise especially fasting BG. They have adapted to burning ketones. Even your brain can adapt to burning ketones. However, it seems a few tissues still need glucose which your liver supplies via gluconeogenesis.
However, even people who are not a diabetic will react this way. Your insulin levels during this time while on the keto diet remain low. If you do a HOMA-IR test/calculation, you should be insulin sensitive. Meaning very low insulin with a little higher FBG.
It takes 1-3 days of consuming carbs at about 100-150 grams to switch back over to adapt to glucose.
However, I think a lot of people "believe" they are on in ketosis, but you need to be very strict about consuming high fat, enough protein and really low carbs, or test using keto strips / meter to be sure you really are in ketosis.
Blogs say this sort of higher than expected BG while in ketosis is healthy, I haven't tried to find scientific evidence that this is true, but it seems like it often happens.
Higher Fasting Glucose on Ketogenic Diets: Reason to Worry?
Long Term Ketosis, Insulin Resistance & Physiologic Glucose Sparing
