Insulin is a peptide hormone produced by pancreatic beta cells that regulates glucose metabolism and cellular energy storage. Fasting insulin levels reflect the body's baseline insulin production and can indicate insulin resistance when elevated, a key feature of metabolic dysfunction and type 2 diabetes risk. Insulin facilitates glucose uptake into cells, promotes glycogen synthesis in liver and muscle, and inhibits lipolysis while promoting lipogenesis. In the fasting state, insulin levels should be low as glucose homeostasis is maintained through hepatic glucose production and minimal peripheral glucose uptake.
Fasting insulin measures the basal output of insulin from pancreatic beta cells. It is one of the earliest detectable markers of insulin resistance, often becoming elevated years before fasting glucose or HbA1c rise above normal. Paired with fasting glucose, it enables calculation of HOMA-IR (homeostatic model assessment of insulin resistance).
Elevated fasting insulin (generally >10-15 µIU/mL, lab-dependent) indicates that the pancreas is producing more insulin than normal to maintain euglycemia — a hallmark of insulin resistance. Very low levels may indicate beta-cell dysfunction or type 1 diabetes. Insulin levels vary significantly with fasting duration, stress, and recent carbohydrate intake.
Exercise acutely improves insulin sensitivity by increasing glucose transporter (GLUT4) translocation to the cell membrane independent of insulin signaling. However, sleep deprivation, psychological stress, and high-cortisol states can impair insulin sensitivity even in highly trained individuals. Fasting insulin tracked alongside glucose provides a more complete picture of metabolic efficiency than glucose alone.
Turnaround Time
3 days (up to 12 days)
Fasting Required
No
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