Interesting reading on prolonged fasting and calorie restriction:
PF [prolonged fasting] cycles lasting 2 or more days, but separated by at least a week of a normal diet, are emerging as a highly effective strategy to protect normal cells and organs from a variety of toxins and toxic conditions while increasing the death of many cancer cell types. PF causes a decrease in blood glucose, insulin, and insulin-like growth factor 1 (IGF-1) and is accompanied by autophagy. Recently, we have shown that PF causes a major reduction in the levels of white blood cells followed by stem-cell-based immune system regeneration upon refeeding. Others have reported on the role of PF in causing major decreases in liver and body mass in rats. However, prolonged water-only fasting is difficult for the great majority of the population, and its extreme nature could cause adverse effects, which include the exacerbation of previous malnourishments and dysfunctions, particularly in old and frail subjects. These concerns point to the need for dietary interventions that induce PF-like effects while minimizing the risk of adverse effects and the burden of complete food restriction.