If you are refering to the HbA1c for the characterization of being prediabetic, take into account that it is an estimator that averages over 8-12 weeks.
Don't confuse Keto, etc. as "high protein", its primarily a very low carb diet, "moderate protein" and "high fat". Too much protein also isn't ideal for Type 2 diabetes or the various stages that lead up to it. One thing that surprised me was for example, how Whey protein can also spike up blood sugar (so much for post-workout whey drinks, etc.)
I recommend the books and videos of Dr. Jason Fung on fasting, as I think he makes a compelling case for the layman how fasting varieties can be beneficial. He is a nephrologist, and since kidney issues are common with diabetes patients, he had many diabetes patients in his office and had good succes with them bettering their condition using fasting methods.
Obligatory: I am not a doctor and you should not swap out medical supervision for random internet advice, but Dr. Jason Fung is definitely worth checking out.
Ok, I hope that wasn't too much of unsolicited advice for you. I wish you all the best and hope that you can get on top of things which whatever method works for you.