The brain and nervous system require the full complement of essential nutrients and energy to develop and maintain their neurons and supporting cells. A deficiency of any one of these essential nutrients may impair the structure or functionality of the neurologic system.

Stroke is the most common life-threatening neurologic disease. Other neurologic conditions are, epilepsy, chronic headaches, and Alzheimer's disease.

The brain metabolizes 100 g to 150 g of glucose per day. During starvation, it adapts and uses ketones, derived from the breakdown of body fat stores, for energy and thus spares blood glucose and conserves body protein.

Severe deficiencies of vitamins, especially the B-complex group, impair nervous system function. Thiamin deficiency causes beriberi neuropathy as well as a peripheral neuropathy and polyneuritis that leads to paralysis of the eye muscles, loss of muscular coordination, and memory loss, especially in long-term alcoholics. Inadequate niacin intake causes pellagra, with symptoms that include intellectual impairment and dementia. Deficiency caused by vitamin B12 malabsorption in untreated pernicious anaemia, or as a result of a long term deficient vegetarian diet, can result in subacute degeneration of the spinal cord, optic nerves, cerebral white matter, and peripheral nerves. Severely deficient intakes of other vitamins of the B-complex group also