The Warning Sign That Shows Up Years Before Diabetes Does
The years-long process that precedes a diabetes diagnosis
Type 2 diabetes doesn't appear suddenly — it's typically the endpoint of years of gradually worsening insulin resistance, most of which is invisible on a standard fasting glucose test until relatively late in the process.
HbA1c: The 3-Month Average
HbA1c measures the percentage of red blood cells with glucose attached, reflecting average blood sugar over roughly the preceding three months — making it far more informative than a single fasting glucose snapshot, which only captures blood sugar at one moment in time. Below 5.7% is considered normal; 5.7–6.4% is classified as prediabetes; 6.5% or above meets the threshold for diabetes. Critically, prediabetes is genuinely reversible through lifestyle change at that stage, which is precisely why catching it early matters.
Fasting Insulin: The Earlier Warning Sign
Insulin resistance develops well before blood sugar itself rises out of the normal range — the pancreas compensates by producing more insulin to keep glucose normal, sometimes for years, before that compensation eventually fails and glucose starts climbing. Fasting insulin, paired with fasting glucose, can be combined into a single number that estimates how insulin-resistant your body currently is — a calculation called HOMA-IR (Homeostasis Model Assessment of Insulin Resistance), developed in the 1980s and still widely used in research and clinical practice today[6]. Fasting insulin below roughly 10 mIU/L (a standard unit for insulin concentration in blood) is generally considered a reasonable target, though reference ranges vary by lab — the key practical point is that this test needs to be specifically requested, since it isn't part of a standard metabolic panel, and a normal fasting glucose reading does not rule out meaningful insulin resistance underneath it.
Why Catching This Early Matters So Much
The insulin-resistance stage, before glucose itself becomes abnormal, is the point at which lifestyle intervention is most effective and most likely to fully reverse the trajectory. Once diabetes is established, management shifts from reversal toward control — still valuable, but a meaningfully different and harder proposition than catching insulin resistance early.
Resistance training and aerobic exercise both independently improve insulin sensitivity, largely by increasing glucose uptake into muscle tissue.
Reducing refined carbohydrate and ultra-processed food intake blunts the exaggerated insulin spikes that drive resistance over time; see the Nutrition guide for the specific dietary levers.
Reducing visceral fat specifically is one of the more direct levers on insulin sensitivity, more so than total body weight alone.
Adequate sleep — even short-term sleep restriction measurably reduces insulin sensitivity. Sleep restriction also disrupts appetite-regulating hormones, a related but separate effect covered in the Sleep guide.
Signs Worth Noticing
None of this requires a blood draw to start noticing. Some signs tend to show up early, while insulin resistance is still the main problem and still fully reversible; others only appear later, once blood sugar itself has become elevated — it's worth knowing which is which.
Darkened, velvety patches of skin (acanthosis nigricans) — commonly on the neck, armpits, or groin — is an early-stage-associated sign, often appearing while insulin resistance is still reversible.
Skin tags, particularly in clusters, are associated with the same early insulin-resistance stage.
Fatigue after carbohydrate-heavy meals, and feeling hungry again shortly after eating, are both early-stage-associated signs, reflecting the exaggerated insulin swings that come with resistance.
Difficulty losing weight despite real effort, particularly around the abdomen, is another early-stage-associated sign.
Increased thirst and frequent urination is a later sign — it only appears once blood sugar itself is elevated, not merely insulin resistance, and typically points toward prediabetes or diabetes rather than the earlier, reversible stage.
Slow-healing cuts and frequent infections are also later signs, generally appearing once diabetes is established.
Blurred vision is a later sign as well, appearing once blood glucose is significantly elevated.
Section takeaway
By the time fasting glucose is abnormal, insulin resistance has typically been developing for years. Fasting insulin, requested specifically alongside fasting glucose, catches the process at its most reversible stage — well before an HbA1c or fasting glucose reading would flag anything, and often before any physical sign appears at all.