WebMD takes a look at a recent study on the biochemistry of calorie restriction: "The results showed that mice that were fed 30% to 40% fewer calories produced more nitric oxide than those who followed an unrestricted diet. Calorie restriction also caused the mice to increase production of another chemical messenger that stimulated production of new mitochondria (the main energy source in cells) and increased oxygen consumption and expression of a protein previously shown to play a role in calorie restriction's effect on life span. These beneficial effects of calorie restriction were not found in mice that lacked the enzyme necessary to synthesize nitric oxide. Therefore, researchers say the findings suggest that nitric oxide may play a critical role in calorie restriction's effect on longevity."

Link: http://my.webmd.com/content/Article/113/110801.htm