Scientists are making progress in understanding connections between the Sirt1 protein, metabolic regulation and life span: "Sirt1 is referred to as Sir2 in lower organisms where it has previously proven to be a key to aging and longevity: Increasing the amount of Sir2 dramatically extends life spans in experimental yeast, worms and flies. ... In mammals, scientists have shown that restricting calories can extend life span and also leads to an increase in Sirt1, the mammalian version of Sir2. ... Sirt1 is probably a very important regulator that integrates cellular response to different types of nutrients, such as glucose, amino acids, and fatty acids." We can hope that a full understanding of the mechanisms of calorie restriction will lead to therapies that can improve on gains in healthy life span obtained via this method.