Insulin
Also known as: Fasting Insulin
What Does Insulin Measure?
Insulin is a hormone produced by the beta cells of the pancreas that regulates blood sugar (glucose) levels. A fasting insulin test measures the amount of insulin circulating in your bloodstream after you have not eaten for at least 8-12 hours. This gives a baseline reading of how much insulin your body needs to maintain normal blood sugar levels at rest, without the influence of recently consumed food.
Why Does Insulin Matter?
Fasting insulin is one of the most clinically valuable yet underutilized biomarkers for assessing metabolic health. Elevated fasting insulin — even when blood sugar appears normal — is one of the earliest warning signs of insulin resistance, a condition where cells stop responding effectively to insulin. Insulin resistance is a root driver of type 2 diabetes, obesity, polycystic ovary syndrome (PCOS), cardiovascular disease, non-alcoholic fatty liver disease, and certain cancers. By detecting high insulin early, clinicians and patients can intervene with lifestyle changes before blood sugar levels become abnormal, making fasting insulin a critical preventive health tool.
Normal Ranges
Males
2–20 µIU/mL (fasting); optimal metabolic health typically associated with levels below 10 µIU/mL
Females
2–20 µIU/mL (fasting); optimal metabolic health typically associated with levels below 10 µIU/mL
Children
Varies by age and puberty stage; generally 2–13 µIU/mL for prepubertal children
Causes of High Levels
- Insulin resistance — cells become less sensitive to insulin, causing the pancreas to secrete more to achieve the same effect
- Type 2 diabetes or prediabetes — chronically elevated blood glucose stimulates excess insulin production
- Obesity and excess visceral (abdominal) fat — fat tissue, especially around the abdomen, promotes insulin resistance
- Insulinoma — a rare, benign tumor of the pancreas that autonomously secretes excessive amounts of insulin
- Polycystic ovary syndrome (PCOS) — a hormonal condition strongly linked to hyperinsulinemia and insulin resistance
- Cushing's syndrome — excess cortisol promotes glucose production and insulin resistance, raising insulin levels
Causes of Low Levels
- Type 1 diabetes — autoimmune destruction of pancreatic beta cells leads to little or no insulin production
- Late-stage type 2 diabetes — prolonged beta cell burnout from years of overproduction can eventually reduce insulin output
How to Improve Your Insulin
Diet
- Reduce refined carbohydrates and added sugars (white bread, sugary drinks, pastries) which spike blood glucose and demand excess insulin
- Follow a lower-carbohydrate or Mediterranean-style diet rich in vegetables, legumes, healthy fats, and lean proteins to reduce insulin demand
- Increase dietary fiber intake from vegetables, legumes, and whole grains to slow glucose absorption and blunt insulin spikes
- Practice time-restricted eating or intermittent fasting (e.g., 16:8 protocol) to allow insulin levels to drop and improve sensitivity
- Include foods rich in polyphenols such as berries, green tea, olive oil, and dark chocolate, which have been shown to improve insulin sensitivity
Supplements
- Berberine 500mg 2–3 times daily — clinically shown to improve insulin sensitivity and reduce fasting insulin comparable to some medications
- Magnesium 300–400mg daily — magnesium deficiency is strongly associated with insulin resistance; supplementation can improve sensitivity
- Alpha-lipoic acid (ALA) 300–600mg daily — a potent antioxidant shown to improve insulin-stimulated glucose uptake in muscle tissue
- Inositol (myo-inositol) 2–4g daily — particularly effective in PCOS-related insulin resistance; acts as a secondary messenger for insulin signaling
Related Biomarkers
Frequently Asked Questions
What is a good fasting insulin level for optimal health?
While most laboratory reference ranges list up to 20–25 µIU/mL as 'normal,' many metabolic health experts consider optimal fasting insulin to be below 10 µIU/mL, with ideal levels often cited between 2–6 µIU/mL. Levels in the high-normal range (10–20 µIU/mL) can still indicate early insulin resistance even if blood sugar appears completely normal. This is why fasting insulin is such a powerful early warning tool.
Can I have high insulin with normal blood sugar?
Yes, and this is actually very common in early insulin resistance. When cells become less sensitive to insulin, your pancreas compensates by secreting more insulin to keep blood glucose in the normal range. This phase — called compensated insulin resistance or hyperinsulinemia — can persist for years before blood sugar rises enough to be flagged. This is why checking fasting insulin alongside fasting glucose gives a much more complete picture of metabolic health.
How do I prepare for a fasting insulin test?
You should fast for at least 8–12 hours before the blood draw, consuming only water during this period. Avoid exercise the morning of the test, as physical activity can temporarily alter insulin levels. Some medications, including corticosteroids, certain blood pressure medications, and birth control pills, can affect insulin levels, so inform your doctor about any medications you are taking. The test is a simple blood draw and results are typically available within 1–2 business days.