Insulin is a pancreatic hormone that plays a vital role in carbohydrate and lipid metabolism. Insulin regulates glucose concentrations by:
- Promoting glycolysis - the uptake of glucose by cells for energy
- Stimulating glycogenesis - the conversion of excess blood glucose to glycogen storage in the liver
- Inhibiting glycogenolysis - the conversion of glycogen back to glucose
- Inhibiting gluconeogenesis - the formation of glucose from noncarbohydrates
Insulin increases lipid synthesis in the liver and fat cells and inhibits lipolysis, the release of non-esterified fatty acids (NEFAs) from triglycerides in fat and muscle cells. Insulin also promotes protein synthesis.
If insulin resistance occurs, carbohydrate and lipid metabolism are impaired. Insulin resistance ordinarily results in increased insulin levels as the body senses a need for more insulin action. The impaired insulin action results in elevated plasma glucose levels. The increase in lipolysis increases blood concentrations of NEFAs and causes abnormal blood lipid levels.