Towards a molecular understanding of adaptive thermogenesis

Obesity results when energy In lake exceeds energy expenditure. Naturally o ccurring genetic mutations, as well as ablative lesions, have shown that th e brain regulates both aspects of energy balance and that abnormalities in energy expenditure contribute to the development of obesity. Energy can be expended by performing work or producing heat (thermogenesis). Adaptive the rmogenesis, or the regulated production of heat, is influenced by environme ntal temperature and diet. Mitochondria, the organelles that convert food t o carbon dioxide, water and ATP are fundamental in mediating effects on ene rgy dissipation. Recently there have been significant advances in understan ding the molecular regulation of energy expenditure in mitochondria and the mechanisms of transcriptional control of mitochondrial genes. Here we expl ore these developments in relation to classical physiological views of adap tive thermogenesis.