Lowered dietary protein leads to a longer life, acting in much the same way as calorie restriction. Here researchers delve more deeply into the underlying mechanisms: "Mitochondria act as the 'powerhouse' of the cells. It is well known that mitochondrial function worsens with age in many species ... Our study shows that dietary restriction can enhance mitochondrial function hence offsetting the age-related decline in its performance ... The researchers report the unexpected finding that while there is a reduction in protein synthesis globally with the low protein diet, the activity of specific genes involved in generating energy in the mitochondria are increased ... That activity, which takes place at the level of conversion of RNA to protein, is important for the protective effects of dietary restriction ... There have been correlative studies that show mitochondria change with dietary restriction, this research provides a causal relationship between diet and mitochondrial function ... mitochondrial genes are converted from RNA to protein by a particular protein (d4EBP). Flies fed a low protein diet showed an uptick in activity of d4EBP, which is involved in a signaling pathway that mediates cell growth in response to nutrient availability called TOR (target of rapamycin). ... d4EBP is necessary for lifespan extension upon dietary restriction. When the activity of the protein was genetically 'knocked out' the flies did not live longer, even when fed the low protein diet. When the activity of d4EBP was enhanced, lifespan was extended, even when the flies ate a rich diet."