What Is a Fasting Insulin Test?
A fasting insulin test measures the amount of insulin in your blood after you have gone at least eight hours without eating or drinking.
Insulin is a hormone produced by the pancreas that helps regulate blood glucose, or blood sugar. When blood glucose rises after a meal, the pancreas releases insulin. Insulin then signals cells throughout the body to absorb glucose from the bloodstream and use or store it for energy.
When cells become less responsive to insulin, the pancreas produces more insulin to keep blood sugar within a normal range. This condition is called insulin resistance. As the pancreas compensates, fasting insulin levels may rise even while fasting glucose and HbA1c remain normal.
Why Does Fasting Insulin Matter?
Fasting insulin may reveal signs of metabolic dysfunction before standard blood sugar tests become abnormal.
- Provides an early warning of insulin resistance. Fasting insulin can become elevated before blood sugar reaches the prediabetes or type 2 diabetes range.1
- Provides insight into overall metabolic health. Elevated fasting insulin is associated with insulin resistance, hypertension, fatty liver disease, metabolic syndrome, and increased cardiovascular risk.2
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How to Interpret Fasting Insulin Levels
- Optimal: 2-6 uIU/mL
- Acceptable: 2-8 uIU/mL
- Borderline: 8-10 uIU/m
>10: suggests increasing likelihood of insulin resistance, particularly if accompanied by elevated triglycerides, low HDL, increased waist circumference.
>15-18: commonly associated with significant insulin resistance
(Ranges may vary slightly by lab)
Standard reference ranges represent the middle 95% of healthy individuals but don’t necessarily reflect levels associated with longevity. Optimal ranges are derived from clinical guidelines, peer-reviewed research, and real-world outcomes data, with an emphasis on levels associated with peak functioning and reduced disease risk.
Benefits of Optimizing Fasting Insulin
- Earlier detection of insulin resistance
- A lower risk of progressing to prediabetes or type 2 diabetes
- Healthier blood pressure and cardiovascular risk markers
- Improved insulin sensitivity
- Reduced risk of metabolic syndrome
- Reduced visceral fat accumulation
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Low Fasting Insulin Levels
Low levels of fasting insulin generally means your body does not need much insulin to keep blood sugar stable. When fasting glucose is also within a healthy range, this typically suggests good insulin sensitivity.
However, if fasting insulin is low and blood sugar is high, the pancreas may not be producing enough insulin. This pattern can suggest type 1 diabetes, advanced type 2 diabetes, or certain other conditions affecting pancreatic function.
High Fasting Insulin Levels
High fasting insulin, also called hyperinsulinemia, usually means the pancreas is producing additional insulin to compensate for reduced insulin sensitivity. Fasting insulin can rise years before blood sugar rises, making it one of the earliest measurable signs of declining metabolic health
This may be an early sign of insulin resistance, particularly when fasting glucose or HbA1c is still within the standard range. Over time, the pancreas may no longer be able to produce enough insulin to compensate, allowing blood sugar to rise and increasing the risk of prediabetes and type 2 diabetes.
Symptoms:
High fasting insulin often doesn’t cause noticeable symptoms, which is why it’s important to check for it with a blood test. When symptoms or related metabolic changes occur, they may include:
- Fatigue, especially after meals
- Difficulty losing weight despite caloric restriction
- Brain fog and difficulty concentrating
- Strong cravings for carbohydrates or sugar
- Elevated blood pressure or triglycerides (may appear on labs before symptoms do)
- Increased waist circumference
Causes:
- Excess body fat, particularly visceral (abdominal) fat
- Insulin resistance
- Diet high in refined carbohydrates, added sugars, and ultra-processed foods
- Sedentary lifestyle and low muscle mass
- Chronic poor sleep or sleep apnea
- Chronic psychological stress
- Genetic predisposition to insulin resistance
- Certain medications, including corticosteroids and some antipsychotics
- Polycystic ovary syndrome (PCOS) in women
Healthspan Impacts:
- Higher risk of hypertension and coronary heart disease
- Progression to prediabetes and type 2 diabetes
- A higher risk of all-cause mortality 3
- Accelerated fat storage
- Greater difficulty maintaining a healthy body composition
- Non-alcoholic fatty liver disease (NAFLD) / Metabolic dysfunction-Associated Steatotic Liver Disease (MASLD)
How Hone Treats Out of Range Fasting Insulin Levels
Your Hone physician references results from a fasting insulin test alongside other metabolic markers including fasting glucose, HbA1c, triglycerides, and HDL cholesterol. This provides a more complete picture of insulin sensitivity and helps determine whether lifestyle changes, additional evaluation, or medical treatment may be appropriate.
Fonseca, V (2008). Early identification and treatment of insulin resistance.
↑Xun P, et al. (2013). Fasting insulin concentrations and incidence of hypertension, stroke, and coronary heart disease.
↑Zhang X, et al. (2017). Fasting insulin, insulin resistance, and risk of cardiovascular or all-cause mortality.
↑Gui J, et al. (2022). Berberine on metabolic profiles in type 2 diabetes mellitus: a meta-analysis.
↑Veronese N, et al. (2016). Effect of magnesium supplementation on glucose metabolism in people with or at risk of diabetes: a systematic review and meta-analysis.
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Reviewed for Accuracy by Our Medical Review Board
This biomarker information has been reviewed by a member of Hone’s medical review board. As part of the medical review team, physicians fact-check this content against the latest research and their own experience treating their patients.
Ashley Winter, M.D., is a board-certified urogynecologist trained at Weill Cornell and Cleveland Clinic. She specializes in female and male sexual dysfunction, urinary issues, genital pain, and hormone therapy.
James Staheli, D.O., is the Medical Director for Broad Health, Hone Health’s affiliated medical practice and a family medicine doctor in Atlanta, Georgia.
