The practice of calorie restriction, reducing calorie intake by up to 40% while still obtaining optimal levels of micronutrients, is the most studied method by which aging can be slowed. Calorie restriction produces sweeping changes in the operation of metabolism, of which the most notable and relevant are probably the increased levels of cellular recycling and repair processes. Certainly, calorie restriction fails to slow aging in lineages where the cellular maintenance processes of autophagy are disabled, which is fairly compelling evidence for the benefits to primarily result from better maintenance of cells.