The practice of calorie restriction slows almost all aspects of aging examined to date: "researchers described experiments with mice showing that a 25% reduction in calories activated a single enzyme, Sirt3, that helped preserve hearing. Although small numbers of people practice strict caloric restriction - consuming just 1,000 to 1,500 calories a day - scientists concede that such a diet is exceedingly difficult. But there may be other ways to achieve the same benefits. ... If we can find compounds that activate Sirt3, we may be able to obtain some of the benefits of caloric restriction without having to restrict our calories. ... [researchers] carried out experiments with normal mice and mice without the Sirt3 enzyme. In one experiment both groups were fed the 25% reduced calorie diet for 10 months. The diet had the same weight loss effect on both groups. Although the diet delayed hearing loss at various frequencies in the normal mice, it did not work at all in the mice lacking Sirt3. ... What seems to happen that drives caloric restriction is that the organism senses it is under stress. There are then metabolic changes that favor self-preservation. ... Under normal conditions, he said, levels of Sirt3 are low. Caloric restriction appears to boost levels of Sirt3 and the boost helps the cells' energy factories, called mitochondria. The mitochondria make not only the energy, but also atoms called free radicals, which damage cells and advance the effects of aging. When Sirt3 levels rise, however, they reduce production of the harmful free radicals. One result is less damage to cells, including the cells of the inner ear."