Nutrition affects brain chemistry in humans and other animals. Everyone experiences the fact that food and nutrition alter mood and behavior. Indeed, food can be a strong conditioning stimulus. One exposure to an adverse stimulus coupled with a particular food can cause a lifetime aversion to that food (see Chap. 50). The neurochemical mechanisms of how diet alters brain function are beginning to be known. Alterations of diet and nutrition based on sound neurochemical and other scientifically valid observations allow the use of diet as a rational and “natural” way to deal with disabilities related to the nervous system, including certain diseases.

The brain is sensitive to changes in diet. It depends on a continuous supply of nutrients from the blood, some of which are synthesized in other organs of the body, such as choline. Others, which cannot be synthesized in mammalian systems at all, are “essential” components that must be furnished by the diet. These essential nutrients include vitamins, amino acids and fatty acids. Studies of deficiencies of vitamins and other nutrients and elements, such as iodine, provide important insights into understanding brain metabolism.

Nutrition can alter brain function in short time frames, for example, by altering neurotransmitters and neuronal firing, and in the long-term, such as by altering membrane structure. The importance of proper nutrition during brain development has been appreciated for several decades. That the nutritional requirements of the brain of mature and aged individuals may differ from those of the young was established more recently. Genetics also affects dietary needs. Although classic vitamin and other nutritional “deficiencies” are major public health concerns in underdeveloped countries, they also occur in industrialized societies. Vitamin insufficiencies can occur secondary to alcohol or drug abuse or other psychiatric disorders, as a result of genetic variation or because particular age groups have special requirements. Nutritional therapy of neurodegenerative disorders in children has been successful in the past and may eventually provide a productive approach to the treatment of common adult neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases, that encompass complex interactions of genetics and the environment. In this chapter, the effects of diet on normal brain function are discussed and the implications for brain disease are presented.