Insulin resistance means the cells in your muscle, liver and fat tissue respond weakly to insulin, so the pancreas has to release more insulin to move the same glucose out of the blood. For a long time the extra insulin works. Glucose stays normal, and the only thing that has changed is how hard the pancreas is working to keep it there.

What insulin actually does

Insulin is the signal that tells muscle to take up glucose after a meal, tells the liver to stop producing its own glucose, and tells fat tissue to hold on to stored fat. When that signal is weak, the liver keeps releasing glucose it does not need to release and muscle takes up less. The pancreas compensates by raising insulin output. High insulin with normal glucose is the earliest stage, and it does not show up on a standard fasting glucose result.

Why blood sugar rises only later

Insulin resistance rarely announces itself. Glucose drifts upward only once the beta cells of the pancreas can no longer keep up with the extra demand. That is why someone can be insulin resistant for years and be told every year that their sugar is fine. The CDC estimated 115.2 million US adults had prediabetes in 2023, and most people with it have no symptoms.

What drives insulin resistance

Fat stored inside the liver and around the organs, low physical activity, short or broken sleep, obstructive sleep apnea, PCOS, pregnancy, and medicines including glucocorticoids and some antipsychotics all reduce insulin sensitivity. NIDDK lists overweight, physical inactivity, age 35 and over, family history, PCOS and sleep apnea among the factors that raise risk. Genetics set the starting point. Muscle mass, sleep and where fat is stored move it in either direction.

Stage	Fasting glucose	What insulin is doing
Insulin sensitive	Below 100 mg/dL	A normal amount of insulin holds glucose steady
Compensated insulin resistance	Below 100 mg/dL	Higher insulin output keeps glucose normal
Prediabetes	100 to 125 mg/dL	Insulin output no longer covers the gap
Type 2 diabetes	126 mg/dL or above	Beta cell function has dropped further

If you want to know where you sit, ask for a fasting glucose, an HbA1c and a lipid panel, and add a two hour oral glucose tolerance test if those come back borderline. Watch waist measurement and strength training rather than scale weight alone, because muscle is the largest site of glucose disposal in the body. Recheck within a year, and sooner if any value already sits in the prediabetes range.

The 2026 ADA Standards of Care define prediabetes as fasting plasma glucose 100 to 125 mg/dL (impaired fasting glucose), two hour plasma glucose 140 to 199 mg/dL on a 75 g oral glucose tolerance test (impaired glucose tolerance), or A1C 5.7 to 6.4 percent. Diabetes is fasting plasma glucose 126 mg/dL or above, two hour plasma glucose 200 mg/dL or above, A1C 6.5 percent or above, or a random glucose 200 mg/dL or above with symptoms.

Insulin resistance itself has no diagnostic threshold in these criteria. Surrogates used in clinical reasoning include a raised triglyceride to HDL ratio, alanine aminotransferase elevation with hepatic steatosis on imaging, acanthosis nigricans, and central adiposity. None of these is diagnostic on its own.

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What insulin actually does

Why blood sugar rises only later

What drives insulin resistance

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