Calorie restriction or Caloric restriction (CR) is the practice of limiting dietary energy intake in the hope that it will improve health and retard aging. In human subjects, CR has been shown to lower cholesterol, fasting glucose, and blood pressure. Some consider these to be biomarkers of aging, since there is a correlation between these markers and risk of diseases associated with aging. Except for houseflies, animal species tested with CR so far, including primates, rats, mice, spiders, Drosophila, C. elegans and rotifers, have shown lifespan extension. CR is the only known dietary measure capable of extending maximum lifespan, as opposed to average lifespan. In CR, energy intake is minimized, but sufficient quantities of vitamins, minerals and other important nutrients must be eaten.