Understanding Fasting Insulin: Normal vs Optimal Ranges

?What is Fasting Insulin?

Fasting insulin measures the level of insulin in the blood after an overnight fast. Insulin is the hormone produced by pancreatic beta cells that enables glucose to enter cells. Fasting insulin reflects baseline pancreatic insulin secretion and is one of the most sensitive early markers of insulin resistance — often becoming elevated years before fasting glucose rises.

!Why It Matters

Chronic hyperinsulinaemia (high insulin) signals insulin resistance and is associated with obesity, type 2 diabetes, cardiovascular disease, certain cancers, and accelerated ageing. Dr. Peter Attia and metabolic medicine experts consider fasting insulin one of the most underutilised metabolic tests. A fasting insulin above 10–15 µIU/mL often indicates significant insulin resistance even when fasting glucose is still 'normal'.

Reference Ranges

Lab normal ranges may vary between laboratories. Optimal and longevity targets are based on research literature and should be interpreted with your physician.

Symptoms of Imbalance

• High insulin itself rarely causes direct symptoms
• Fatigue and energy crashes, especially after carbohydrate-rich meals
• Difficulty losing weight despite calorie restriction
• Abdominal fat accumulation
• Brain fog and poor concentration
• Acanthosis nigricans (dark patches on neck/armpits) in severe cases

How to Improve Your Levels

• 1Low-carbohydrate or ketogenic diet — the most powerful intervention for reducing insulin levels
• 2Time-restricted eating and intermittent fasting reduce baseline insulin secretion
• 3High-intensity interval training (HIIT) dramatically improves insulin sensitivity
• 4Strength training increases muscle glucose uptake
• 5Lose body fat, particularly visceral (abdominal) fat
• 6Reduce stress and prioritise sleep
• 7Berberine, metformin, or GLP-1 agonists under medical supervision if lifestyle is insufficient

When to Test

Not included in standard blood panels — must be specifically requested. Test fasting (12 hours). Particularly valuable if you have weight issues, family history of diabetes, high triglycerides, low HDL, or elevated HbA1c despite normal fasting glucose.

Related Biomarkers