How to Improve my Insulin Sensitivity

I dropped from 276 to 258 in 3 months. My A1C last November was 6.9. I have improved my diet a lot. As per my CGM, my blood sugar average is about 112 now. I walk about 8k to 10k a steps a day. However on the few occasions where I do eat refined carbs my blood sugar skyrockets. For example I had 1 kollache for breakfast and my blood sugar went from 101 to 210 within 1 hour. Is this normal for non diabetics too? If not, how can I improve my sensitivity.