The excellent review of fasting written by Valter Longo and Mark Mattson and published in February 2014 has passed its first birthday a while back, so it’s now available to the public at Cell Metabolism (including the PDF) without a subscription. While there’s a lot of scientific lingo, much of the article can be easily understood by an interested reader without specialized education. The article strongly supports the many positive changes that can result from intermittent fasting (fasting one day or less at intervals of less than a week) and periodic fasting (fasting 48 or more consecutive hours at longer intervals than used in IF).
Longo and Mattson start by differentiating fasting and starvation. They define fasting as a 12-hour to three-week period without eating, and starvation as chronic nutritional insufficiency that can result in degeneration and death.
“The ketone bodies, free fatty acids and gluconeogenesis allow the majority of human beings to survive 30 or more days in the absence of any food, and allow certain species, such as Emperor penguins, to survive over five months without food.”
The authors point out that the state of being hungry, which is the associated with the presence of certain neuroendocrine (brain- and nerve-related) hormones, may be essential to the benefits of fasting and intermittent fasting (IF) in animals. The authors also discuss an intriguing phenomenon called differential stress resistance and sensitization (DSR/DSS), which describes why fasting can be protective to normal cells during chemotherapy for cancer. Normal cells can deal with the additional mild stress of fasting on top the poison-like effects of chemotherapy, but the rapidly-dividing cancer cells, growing in a glucose-rich environment, can lose this adaptability, so the cancer cells are more prone to die than the normal ones. The take home lesson is that fasting plus chemotherapy may do a lot better job of treating cancer than chemotherapy (or fasting) alone and have a reduced side effect profile. Studies of these effects are underway.
The authors go on to review the data regarding fasting’s effect on disease models and aging in animals, followed by a summary of the information available on similar effects in humans. After reviewing data indicating that fasting triggers reductions of many biomarkers of aging, neurodegeneration and inflammation, the authors indicate directions for further study and suggest caution in any therapeutic application, especially in individuals of at the extremes of age.