Insulin promotes muscle glucose uptake and metabolism. In presence of insulin muscle cells take up glucose and use it as a source of energy. Insulin also promotes storage of insulin in the form of glycogen in the muscle cells. Later, this glycogen can be broken down to glucose and used as a source of energy. But insulin prevents break down of glycogen to glucose in muscle cells. Only when insulin level is low glycogen can break down to glucose.

Insulin also promotes uptake, storage and use of glucose in liver. After a meal good amount of glucose is absorbed from gastrointestinal tract and come into circulation. This absorbed glucose is taken up by liver cells and converted to glycogen. The liver stores good amount of glycogen. Insulin prevents break down of glycogen in liver. In between meals when both glucose and insulin levels of blood are low, liver glycogen is broken down to glucose and used as fuel.

Insulin promotes conversion of excess glucose into fatty acids and inhibits formation of glucose from fatty acids and amino acids, in the liver. When the amount of glucose entering the liver is more than what can be stored as glycogen or be used for liver cell metabolism, insulin promotes the conversion of this excess glucose into fatty acids.