Insulin is produced which helps body tissues to get glucose from the blood into the body cells where it is used as energy or else for storage as glycogen in the liver. Without insulin, glucose cannot enter the cells and cannot be utilised.

Every time blood glucose concentrations are over 100 mg per dL, insulin is released, generally after a meal. When insulin levels are high, the liver stops producing glucose and stores it in other forms until the body needs it again. Insulin helps body tissues to remove glucose from the blood into the body cells where it is used as energy or else for storage as glycogen in the liver. This makes blood glucose concentrations get back to normal within 2 hours. When glucose levels fall, lowered insulin levels result in the reconversion of glycogen to glucose in the liver.

Higher insulin levels increase anabolic processes such as cell growth, cellular protein synthesis, and fat storage.

Insulin production usually reaches the highest levels one hour after having a meal. This does not happen in people with diabetes. Insufficiency of insulin or insensitivity of cells to insulin (insulin resistance) as in type 2 diabetes and no insulin secreted as in type 1 diabetes results in persistent high levels of blood glucose. This does not happen in normal fashion in people with type 2 diabetes and none is secreted in type 1 diabetes.