From what I remember, drinking coffee increases cortisol, which increases blood glucose. I can’t find specific data point studies about it other than over a week, the group that consumed coffee had an 8 percent higher blood glucose level. Also That coffee use had the potential to reduce insulin sensitivity but also decrease the risk of diabetes.
Anecdotally, I’ve been gulping pots of coffee for ten years and everything’s fine, still lean, still sleeping well. Even if you have a genetic test that tells you if you’re a fast metabolizer, I think you need to try for yourself and see what works.