From an article on fasting:
In their study on fruit fly larvae, the researchers found that the brain responds to nutrient scarcity (like that which occurs during fasting) by reducing synaptic activity. (Synapses are the connecting structures that allow chemical signals to be passed between neurons.) This may essentially be the brain’s way of conserving energy and giving itself a little reboot.
Within only a few hours, dietary restriction triggered a response from molecular pathways that govern synaptic activity, or neurotransmitter release. By reducing the release of neurotransmitters from synapses in the brain, fasting may also give the nervous system a break, the researchers note.
“The process of neurotransmitter release is an energetically costly process,” Haghighi explained in an email to The Huffington Post. “Because of this high requirement for energy, it also generates waste including reactive oxygen species, that could lead to oxidative damage in cells including neurons. … Tuning synaptic activity as a result of fasting might help limit the unwanted oxidative damage in the nervous system.”
Neuroscientists have linked overactive synaptic activity with neurodegenerative diseases such as Alzheimer’s, Huntington’s and Parkinson’s disease, and therefore fasting could be an effective preventative measure.