High insulin levels drive glucose into muscle, fat and liver cells where it is stored for future use. Low insulin levels allow glucose and other fuels to be released into the blood stream.

Overnight and between meals, insulin levels in the blood stream are low and relatively constant. These low levels of insulin allow the body to tap into its stored energy sources (namely glycogen and fat) and also to release glucose and other fuels from the liver. This overnight and between-meal insulin is referred to as background or basal insulin. When you haven’t eaten for a while, your blood glucose level will be somewhere between 60 to 100 mg/dl.

When eating, insulin is rapidly released from the pancreas. The burst of insulin that accompanies eating is called bolus insulin. After a meal, blood glucose levels peak at less than 140 mg/dl and then fall back to the baseline (pre-meal) range. The high levels of insulin help the glucose get out of the blood stream and be stored for future use.

Insulin levels throughout the day

To keep the blood glucose in a narrow range throughout the day, there is a low steady secretion of insulin overnight, fasting and between meals with spikes of insulin at mealtimes.  Adapted: Jacobs DM Care 20:1279, 1997

There are other hormones that work together with insulin to regulate blood glucose including incretins and glucose counterregulatory hormones, but insulin is the most important.