So I have the Heads Up Health App. (Got it when it was free.) I’m not much a tracker usually.'But that being said; I’m so glad I went back and tracked my GKI from when I got really serious back in May about Keto. I couldn’t believe it after 9 days of fasting clean with water only the lowest my GKI got was 1, and highest ketones were 5.5. Blood sugar high and lows were 50 to 112 during that fast This last week (every day) I changed my intermitant fasting from 16 - 8 to 20-4.I’ll admit, I have to push through come about 5 pm; but ll I can say is MIND BLOWN. 
Today my GKI was 1.3, glucose 97 and ketone 4.3… and I have been eating everyday. And I drink some (dry cabernet) wine at night. I have so much energy all day. No afternoon fatigue; and it’s a heck of a lot easier than an extended fast. I do plan to continue extended fasting for the health benefits. I’m 58years old and never been able to keep my weight down my whole life. Actually feeling like lifting a little heavy weight now as my strength has declined the last couple of years.Finally making progress.
The only concern I have is I may not be eating enough in my 4 hr eating window. But I think I am. I tried to track macros and calories and when I got to 1100 calories and and had a little more food left, I thought that should be fine. I just really cant seeing writing down everything I eat. (lifes too short) I’m more of a go how by I feel and eyeball it. LOL!
I hope this helps someone else. I struggled so hard since May with low ketone levels and realize I am more insulin resistant than I thought!