I agree, the walking is definitely helping, not that food intake isn't important, but any sustained cardio for a decent amount of time daily should improve the insulin resistance in your body and be more forgiving on what you are putting into it. I've tried to go by 30 minutes a day at least, currently do around 45 mins 5 days a week, the other 2 at least 15-20 mins of exercise, although all at once. I'm not perfect though and could do better throughout the day, needing to be behind a computer a lot for work isn't always helpful, but I keep myself active.

My grandmother would always tell me to just take a 10 minute walk after larger meals, which gets in 30 minutes after 3 meals. I've never been a big walker myself, but she did it after almost every meal, just walked around the neighborhood, or would do something outside, gardening, yard work, etc. Later in her life she added in a stationary bike because I think she just couldn't keep up with the walking around, but primarily was always a walker and tried to keep herself moving and active.

I think you would be considered a pre-diabetic at this point, which shouldn't change what you are doing, without maintaining it you will likely become a diabetic, especially if there is any family history, but it sounds like you're doing the right things to avoid it so keep it up and don't let your guard down.