What is Fasting Insulin?

When tissues resist insulin's effect, more of it is needed to move the same glucose, so the amount circulating tracks the resistance rather than the sugar itself. Across populations that resistance tracks body fat: insulin rises with weight gained and falls with weight lost.

Fasting Glucose measures the sugar, and Fasting Insulin measures the hormone doing the work of holding it down. HOMA-IR combines the two into a single figure: how much insulin it is taking to hold that much glucose.

Sensitivity to insulin shifts with physical activity, diet and sleep. How much insulin the pancreas is able to produce also sets the figure: the same resistance in the tissues shows as less insulin if the pancreas cannot supply more. That capacity differs between people and changes with age.

The pancreas can raise its output within weeks of a change in sensitivity, and glucose follows only later, once that larger output is no longer enough to hold it steady. Measuring about every four months samples insulin at the stage when it has moved and glucose has not, and each reading set against the last shows whether the change has held across a season. This is Do Health's monitoring schedule, not a general recommendation for everyone.