Ketosis takes like a full day of fasting to reach, becoming ketone adapted takes weeks of ketosis, to stay in ketosis you need to eat less than 20g of carbs. You don’t need to be fat to be insulin resistant, get your fasting insulin and A1C tested, if your fasting insulin is high you are insulin resistant and on the way to pre-diabetes and you will need to change your diet if you are already lean and probably up exercise.
“Ideally, your blood insulin levels should be less than ~6 microunits per milliliter of blood (µU/mL). While ~8–9 µU/mL is the average for men and women, it’s not good to be “average” in this case; a person with 8 µU/mL has double the risk of developing type 2 diabetes as a person with 5 µU/mL.”
Bikman, Benjamin. Why We Get Sick (p. 176). BenBella Books. Kindle Edition.
The general pattern is for people to have insulin resistance long before (~years) it shows up in blood glucose levels, and the numbers you are reporting seem like the normal path to insulin resistance. I’m not saying that’s what’s going on in your case, but there’s no particular reason to assume what you’re reporting is due to something unusual (eg, fasting). The problem in all of this is that glucose is the easy thing to measure, not the best thing to measure, and high glucose is a late sign of problems, not an early sign.