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

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.

The liver both stores and produces glucose

The liver acts as the body’s glucose (or fuel) reservoir, and helps to keep your circulating blood glucose levels and other body fuels steady and constant. The liver both stores and manufactures glucose depending upon the body’s need. The need to store or release glucose is primarily signaled by the hormones insulin and glucagon. During a meal, your liver will store glucose, as glycogen for a later time when your body needs it. The high levels of insulin and suppressed levels of glucagon during a meal promote the storage of glucose as glycogen.

The liver makes glucose when you need it. When you’re not eating – especially overnight or between meals, the body has to make its own glucose. The liver supplies glucose by turning glycogen into glucose in a process called glycogenolysis. The liver also can manufacture necessary glucose by harvesting amino acids, waste products and fat byproducts. This process is called gluconeogenesis.  The liver also makes another fuel, ketones, when glucose is in short supply.  When your body’s glycogen storage is running low, the body starts to conserve the glucose supplies for the organs that always require it. These include: the brain, red blood cells and parts of the kidney. To supplement the limited glucose supply, the liver makes alternative fuels called ketones from fats. This process is called ketogenesis. The hormone signal for ketogenesis to begin is a low level of insulin. Ketones are burned as fuel by muscle and other body organs. And the glucose is saved for the organs that need it.  

Other influencing hormones

There are other hormones other than insulin that affect the blood glucose levels in your body. It is important to know about glucagon, amylin, GIP, GLP-1, epinephrine, cortisol, and growth hormone.

Glucagon

Made by islet cells (alpha cells) in the pancreas, controls the production of glucose and another fuel, ketones, in the liver. Glucagon is released overnight and between meals and is important in maintaining the body’s gluocse and fuel balance. It signals the liver to break down its starch or glycogen stores and helps to form new glucose units and ketone units from other substances. It also promotes the breakdown of fat in fat cells. In contrast, after a meal, when glucose from the ingested food rushes into your bloodstream, your liver doesn’t need to make glucose and glucagon levels fall.  In individuals with Diabetes, the opposite occurs. While eating, their glucagon levels rise, which causes blood glucose levels to rise after the meal.

 

GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide) and amylin

GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide) and amylin are other hormones that also regulate mealtime insulin. GLP-1 and GIP are incretin hormones. When released from your gut, they signal the beta cells to increase their insulin secretion and, at the same time, decrease the alpha cells’ release of glucagon. GLP-1 also slows down the rate at which food empties from your stomach, and it acts on the brain to make you feel full and satisfied. In people with Diabetes these hormones may be deficient to varying degrees which may contritbute to high glucose levels.  This may explain, in part, why individuals with Diabetes do not suppress glucagon during a meal and have high blood glucose levels after a meal.

Amylin is released along with insulin from beta cells. It has much the same effect as GLP-1. It decreases glucagon levels, which will then decrease the liver’s glucose production, slows the rate at which food empties from your stomach, and makes your brain feel that you have eaten a full and satisfying meal. The overall effect of these hormones is to reduce the production of glucose by the liver during a meal to prevent it from getting too high.   

Epinephrine, cortisol, and growth hormone

Epinephrine, cortisol, and growth hormone are other hormones that help maintain blood glucose levels. They, along with glucagon (see above) are called “stress” or “gluco-counter-regulatory” hormones - which means they make the blood glucose rise.  Epinephrine (adrenaline) is released from nerve endings and the adrenals, and acts directly on the liver to promote glucose production (via glycogenolysis). Epinephrine also promotes the breakdown and release of fat nutrients that travel to the liver where they are converted into glucose and ketones. Cortisol is a steroid hormone also secreted from the adrenal gland. It makes fat and muscle cells resistant to the action of insulin, and enhances the production of glucose by the liver. Under normal circumstances, cortisol counterbalances the action of insulin. Under stress or if a synthetic cortisol is given as a medication (such as with prednisone therapy or cortisone injection), cortisol levels become elevated and you become insulin resistant. When you have Diabetes, this means your may need to take more Diabetes medication to keep your blood glucose under control. Growth Hormone is released from the pituitary, which is a part of the brain. Like cortisol, growth hormone counterbalances the effect of insulin on muscle and fat cells. High levels of growth hormone cause resistance to the action of insulin.