5'-adenosine monophosphate-activated protein kinase (AMPK) is an enzyme activated when cellular energy status is threatened. AMPK activates energy-providing processes, while energy-consuming processes are inhibited. AMPK is also involved in regulation of gene expression and in appetite control. Pharmacological activation of AMPK in animal models of the metabolic syndrome leads to marked amelioration of symptoms. Some antidiabetic drugs activate AMPK, and activation also occurs during physical exercise. It is likely that part of the effect of physical activity in preventing the development of diseases related to a sedentary lifestyle is due to activation of AMPK.