Non-esterified fatty acids (NEFA) are the major component of triglycerides, which consist of three fatty acids linked to a glycerol backbone. Hydrolysis of triglycerides in adipose tissue by hormone sensitive lipase liberates NEFAs and glycerol. Low concentrations of NEFAs are normally found in blood. Increased concentrations indicate breakdown of fat (lipolysis), which occurs in response to increased energy demand. Thus, NEFAs are considered a biomarker of negative energy balance, where the supply of glucose is insufficient to meet energy needs.