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 |
Agree on your personal target range with your doctor.
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 may indicate type 1 diabetes, pancreatic insufficiency, or highly restrictive eating. With simultaneously elevated blood glucose, absolute insulin deficiency is a medical emergency.
↑ 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.
✓ What can influence this value
Fasting insulin is influenced by body weight (especially visceral fat), physical activity, diet and calorie intake, sleep, and conditions such as PCOS. Caloric restriction and intermittent fasting can lower the value, and aerobic and strength training are associated with higher insulin sensitivity. Regarding measurement conditions: the value is only meaningful after at least 8 hours without food, and a meal beforehand raises it. The assessment is made by the treating doctor.
When to test
The test is done fasting (8–12 hours without food), and for the HOMA-IR together with fasting glucose. Reasons include screening for metabolic syndrome, overweight, PCOS, fertility issues, performance decline, or assessing diabetes risk. How often it is measured is decided by your doctor.
Frequently asked questions
Why is insulin measured fasting rather than 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.
Is insulin resistance reversible? +
In early stages, insulin resistance is considered reversible. In studies, weight loss in people with overweight improved insulin sensitivity; diet, aerobic and strength training, and sleep are also linked to insulin sensitivity. Whether and how treatment is given is decided by your doctor.
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.
Fasting Insulin
Sources
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.