Fasting Insulin & HOMA-IR

What it is

Fasting insulin measured after an overnight fast. HOMA-IR (homeostatic model assessment of insulin resistance) is calculated as:

HOMA-IR = (fasting insulin in μIU/mL × fasting glucose in mg/dL) / 405

Why it matters

Insulin resistance is the earliest detectable abnormality in the path to type-2 diabetes, often present for a decade before fasting glucose rises out of normal range. Elevated fasting insulin predicts cardiovascular events, cancer incidence, and cognitive decline.

Reference ranges

There is no universally agreed normal. Practical targets:

• Optimal fasting insulin: <~5 μIU/mL (35 pmol/L).
• HOMA-IR: <~1.5 considered insulin-sensitive; >2.5 suggests insulin resistance; >3.5 strongly so.

Reference ranges vary by laboratory and population; interpret longitudinally in an individual rather than against a generic cutoff.

What worsens it

• Excess calories, particularly refined carbohydrate.
• Visceral adiposity.
• Sedentary behaviour.
• Insufficient sleep.

What improves it

• Weight loss (the strongest lever).
• Exercise, especially resistance + zone 2.
• Improving sleep quality.
• Metformin, SGLT2 inhibitors, GLP-1 agonists.

Related entries

HbA1c, Type 2 diabetes, Insulin/IGF-1 signalling.