Ascribe has a more science-focused article on recent work that examines the biochemistry of fasting. "Critical organs rely on sugar -- specifically glucose -- for the energy to function. In people with diabetes, however, the liver doesn't sense the incoming calories, and it keeps making glucose when it shouldn't ... in fasting mice, the liver's production of sugar kicked into high gear because amounts and activities of the two proteins, called sirtuin1 and PGC1-alpha, increased when dietary calories weren't available. Once mice were fed, levels of the two proteins went down and sugar production ceased." This relates to work on the mechanisms of calorie restriction (CR), although the jury is still out on whether alternate methodologies of CR - such as intermittent fasting - are as effective in extending healthy life span.