Adipose tissue is an energy reserve in animals. Adipose cells produce and secrete numerous physiologically important proteins that help regulate whole body metabolism, such as adiponectin leptin. Fasting causes significant changes in nutrient metabolism and many of these changes are controlled by transcription factors that regulate rate-limiting enzymes. An important transcription factor that mediates metabolic processes induced by fasting is peroxisome proliferator-activated receptor alpha (PPAR alpha). PPAR alpha has recently been reported to target a novel gene encoding the secreted protein FIAF (fasting-induced adipose factor). FIAF is expressed predominantly in adipose tissue and is strongly upregulated in white adipose tissue and the liver under fasting conditions. Initial studies sμggest that FIAF represents a novel endocrine signal helping to regulate metabolism, especially under fasting conditions.