My Mother Says that Mark Mattson, Neuroscientist, has done some fascinating studies on what Fasting does for your body and brain.
Intermittent fasting enhances the ability of nerve cells to repair DNA
Fasting stimulates the production of new nerve cells from stem cells in the hippocampus. He also mentions ketones (an energy source for neurons), and how fasting stimulates the production of ketones and that it may also increase the number of mitochondria in neurons. Fasting also increases the number of mitochondria in nerve cells; this comes as a result of the neurons adapting to the stress of fasting (by producing more mitochondria).
By increasing the number of mitochondria in the neurons, the ability for nerons to form and maintain the connections between each other also increases, thereby improving learning and memory ability.