Fasting Insulin
Fasting insulin as an early marker of insulin resistance and metabolic syndrome
Also known as
Definition
Insulin is a peptide hormone from the beta cells of the pancreas that regulates glucose uptake into tissues, inhibits gluconeogenesis, and promotes anabolic processes. Fasting insulin (after ≥ 8 hours without food) is a sensitive early marker for insulin resistance — often abnormal before fasting glucose or HbA1c become pathological. It directly feeds into the HOMA-IR index.
| Parameter | Value |
|---|---|
| Unit | pmol/l (mU/l) |
| Reference Range | < 60 pmol/l (< 10 mU/l); fasting after ≥ 8 hours |
| Optimal Range (lab2go) | < 42 pmol/l (< 7 mU/l) (lab2go Optimum Zone; < 7 mU/l associated with lowest metabolic risk) |
Conversion: 1 mU/l = 6.0 pmol/l (or 7.18 pmol/l per precise WHO definition). US labs use µIU/ml (equivalent to mU/l).
↓ What a low value means
Very low fasting insulin (< 6 pmol/l / < 1 mU/l) may indicate type 1 diabetes, pancreatic insufficiency, or highly restrictive eating. With simultaneously elevated blood glucose, absolute insulin deficiency is a medical emergency. In those adapted to intermittent fasting, values < 25 pmol/l can be healthy and advantageous.
↑ What a high value means
Elevated fasting insulin (> 60 pmol/l / > 10 mU/l) indicates compensatory hyperinsulinemia from insulin resistance. Causes: overweight (especially visceral adiposity), physical inactivity, high-calorie diet, PCOS. Consequences: metabolic syndrome, type 2 diabetes, cardiovascular risk, elevated triglycerides, low HDL, falling SHBG.
✓ How to optimize this marker
Caloric restriction and intermittent fasting (16:8) lower fasting insulin effectively. Aerobic and strength training increase peripheral insulin sensitivity. Low-carb and Mediterranean diets reduce postprandial insulin demand. Omega-3 fatty acids, magnesium, and berberine hydrochloride show insulin-sensitizing effects in studies.
When to test
Always fasting (≥ 8–12 hours, water only) and always with fasting glucose for the HOMA-IR. For metabolic syndrome screening, overweight, PCOS, fertility issues, performance decline, or as an early warning system for diabetes risk. Repeat every 6–12 months with elevated values.
Frequently asked questions
Why measure insulin fasting and not after eating? +
Fasting insulin reflects the basal level after postprandial insulin secretion has resolved. Elevated fasting values show that the pancreas is releasing too much insulin even without a food stimulus — a sign of insulin resistance. Postprandial insulin (e.g., in an OGTT) measures beta cell responsiveness.
What is the difference between insulin resistance and diabetes? +
Insulin resistance is the precursor stage: cells respond less to insulin, so the pancreas compensates by producing more. Blood glucose remains normal initially with elevated insulin. When the beta cells become exhausted and insulin production falls, blood glucose rises — that is type 2 diabetes.
Can insulin resistance be reversed? +
Yes — in early stages, insulin resistance is reversible. Studies show that 10% weight reduction in overweight individuals can improve insulin sensitivity by 50–80%. The combination of dietary change (low-GI/low-carb), aerobic and strength training, and sleep optimization is most effective.
What is hyperinsulinemia and what are its long-term consequences? +
Chronically elevated insulin (hyperinsulinemia) promotes fat storage (inhibiting lipolysis), raises triglycerides, lowers SHBG (affecting sex hormones), favors PCOS in women, promotes cell growth (IGF-1-like effects), and is associated with increased cancer risk.
Sources
Last Reviewed: May 28, 2026 · sina
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.