Lipolysis is the breakdown of fat stored in fat cells. During this process, free fatty acids are released into the bloodstream and circulate throughout the body. Ketones are produced, and are found in large quantities in ketosis (an adaptive metabolic state that occurs when insufficient carbohydrates are present in the diet). Lipolysis testing strips such as Ketostix are used to recognize ketosis.

The following hormones induce lipolysis: epinephrine, norepinephrine, glucagon and adrenocorticotropic hormone. These trigger 7TM receptors, which activate adenylate cyclase. This results in increased production of cAMP, which activates protein kinase A, which subsequently activate lipases found in adipose tissue.

Triglycerides undergo lipolysis (hydrolysis by lipases) and are broken down into glycerol and fatty acids. Once released into the blood, the relatively hydrophobic free fatty acids bind to serum albumin for transport to tissues that require energy. The glycerol also enters the bloodstream and is absorbed by the liver or kidney where it is converted to glycerol 3-phosphate by the enzyme glycerol kinase. Hepatic glycerol 3-phosphate is mostly converted into dihydroxyacetone (DHAP) and then glyceraldehyde 3-phosphate (G3P) to rejoin the glycolysis and gluconeogenesis pathway.