Diabetes is not a single event but a progression - and each stage has its own window where the right action changes the ending.

Stage 1: Insulin resistance (silent)

The body's cells stop responding well to insulin; the pancreas compensates by making MORE
Blood sugar is still normal - no test of sugar finds this stage; the signs are the waist growing, the family history, the sedentary years
Window: widest of all - lifestyle change here prevents everything downstream

Stage 2: Prediabetes (the warning)

The pancreas starts losing the compensation battle: fasting sugar 100-125 mg/dL or HbA1c 5.7-6.4%
Still usually no symptoms - found only by testing
Window: genuinely reversible - structured diet, 150 minutes of weekly activity and 5-7% weight loss cut progression by more than half in the big studies