Inevitably, researchers who focus on slowing aging through metabolic manipulation will uncover ingested compounds that alter metabolism in beneficial ways, and thus very modestly raise life expectancy. Here is an example in mice: "Recent evidence points to a strong relationship between increased mitochondrial biogenesis and increased survival ... Branched-chain amino acids (BCAAs) have been shown to extend chronological life span in yeast. However, the role of these amino acids in mitochondrial biogenesis and longevity in mammals is unknown. Here, we show that a BCAA-enriched mixture (BCAAem) increased the average life span of mice. BCAAem supplementation increased mitochondrial biogenesis and sirtuin 1 expression in primary cardiac and skeletal myocytes and in cardiac and skeletal muscle, but not in adipose tissue and liver of middle-aged mice, and this was accompanied by enhanced physical endurance. Moreover, the reactive oxygen species (ROS) defense system genes were upregulated, and ROS production was reduced by BCAAem supplementation. All of the BCAAem-mediated effects were strongly attenuated in [mice engineered to lack] endothelial nitric oxide synthase." Nitric oxide is important to stem cell and blood vessel function; it is interesting that this effect depends upon that component of metabolism.