What the numbers mean
Fasting glucose of 100–125 mg/dL, or an HbA1c of 5.7–6.4%, is called prediabetes. Above that range is type 2 diabetes. HbA1c reflects your average blood sugar over roughly three months, which is why it doesn't move overnight.
What's happening inside
Cells in muscle, liver and fat stop responding well to insulin. The pancreas compensates by making more of it. For years glucose can look almost normal while insulin quietly climbs — this is why insulin resistance usually starts long before a diagnosis.
Why this stage matters most
Large trials such as the Diabetes Prevention Program found that losing 5–7% of body weight and walking about 150 minutes a week cut progression to type 2 diabetes by 58% — more effective than the medication arm of the same study.