Here is a wonderful paper that suggests a mechanism for the protective effects of fasting with respect to Adult Hippocampal Neurogenesis-The hunger hormone Ghrelin.
There is a close relationship between cognitive performance and nutritional status, but the mechanisms underlying this relationship are not well understood.
The hormone, ghrelin, which is released during food restriction, triggers adaptive responses to improve learning and memory by increasing the formation of new neurones in the adult brain.
The birth of new neurones (neurogenesis) from neural stem cells in the adult mammalian brain is an important process involved in protecting against the age-related decline in cognitive function.
Activation of the hippocampal ghrelin receptor may be a viable therapeutic approach to stimulate neurogenesis and protect against age- and disease-related cognitive decline.
https://www.sciencedirect.com/science/a ... 249#ab0010