Dr. Jain is a consultant in neurology and has no relevant financial relationships to disclose.)
This article describes the role of the brain in nutrition as well as the disorders of the nervous system that result from nutritional disturbances. An example is folic acid deficiency, which has been linked to neural tube defects during early pregnancy. Dietary supplementation with folic acid can prevent neural tube defects. Several other vitamins, minerals, and nutrient factors have been used for the therapy of neurologic diseases, but the role of most of these has not been defined. Oxidative stress has been implicated in the pathogenesis of neurodegenerative disorders. Several studies have shown that antioxidants can block neuronal death in vitro and in animal models of neurodegenerative diseases. Dietary supplementation with antioxidants could, thus, be considered beneficial as a preventive strategy.
• Nutrition plays an important role in the development and function of the nervous system.
• Several neurologic disorders are due to nutritional disturbances.
• An understanding of the mechanisms of actions of nutrients on the brain is important for the use of nutrients to prevent or treat neurologic disorders.
Historical note and terminology
Several neurologic disorders are due to nutritional disturbances. On the other hand, the brain plays an important part in the regulation of nutrition in the rest of the body, and neurologic disorders can result in malnutrition as well. The nutritional environment for the optimal development and function of the CNS has not been properly defined.
The human brain consumes an enormous amount of energy. Despite representing only 2% of the body's total mass, the human brain consumes 20% of the body's total energy because of the increased metabolic need of its neurons. Compared to other primates, humans have proportionally small guts, and most energy is spent on the larger brain. The brain has tripled in size since australopithecines started to walk upright about 3 million years ago, but body size has not even doubled. Of all mammals, humans have the largest brain relative to body size.
Nutrition of the human brain has played an important part in the evolution of Homo sapiens. A shift in the hominid resource base towards more high-quality foods occurred approximately 2 million years ago; this was accompanied by an increase in relative brain size and a shift towards modern patterns of fetal and infant development (Broadhurst et al 1998). The evolution of the human brain, with its high metabolic cost imposed by its large number of neurons, is attributed to humanity's change from a raw diet to a cooked diet that enables individuals to ingest the entire caloric requirement for a day in very little time (Herculano-Houzel 2012). Some of the earliest nonplant foods eaten included fish, the consistent consumption of which could have provided a means of initiating and sustaining cerebral cortex growth without an attendant increase in body mass. The long-chain polyunsaturated lipid ratios of fish are like those found in the human brain and their deficiency at any stage of fetal or infant development can result in irreversible impairment of brain growth. Hence, "brain-specific" nutrition had, and still has, significant potential to affect hominid brain evolution. Other factors, such as caloric restriction, protein malnutrition, and amino acid deficiency, can affect brain weight, brain size, and the nucleic acid content of the brains of offspring.
Ancient systems of medicine relied heavily on diet in the treatment of diseases, including those of the nervous system. Almond nuts were "brain food" in Ayurveda, and certain foods were considered to induce disorders of the nervous system. Fasting has been used to improve health in many alternative health-care systems, and ketogenic diets have been used since the beginning of this century for the treatment of seizures (Wilder 1921).
An association between B12 deficiency and psychiatric disorders was observed by Addison in 1868, when he wrote that the "mind occasionally wanders" in pernicious anemia patients (Moss et al 1987). Clinical trials of nutrition and the brain involving vitamins were conducted in the 20th century. The effect of vitamin deficiency on intelligence was studied by adding vitamin and mineral supplements to the diets of a group of school children in a double-blind, placebo-controlled study that lasted 8 months (Benton and Roberts 1988). The supplement group showed a significant increase in nonverbal intelligence, whereas the placebo group did not. Controversy about the results of this study persists, but the possibility exists that vitamin deficiency may adversely affect behavior and learning capacities (Benton 1991).
Nutrition plays an important role in neurodevelopment in children and in preventing neurodegeneration during aging. The role of the brain in nutrition as well as the disorders of higher cerebral function that result from nutritional disorders will be the focus of this article. Although it is recognized that a dietary supply of macronutrients (protein, carbohydrate, and fat) is essential for human health, a basic knowledge of micronutrients, vitamins, and trace minerals is important for understanding the pathophysiology of some brain disorders and also forms a basis for therapeutic interventions. Advances in understanding of the mechanisms underlying the actions of nutrients on the brain, which involve changes in neurotrophic factors, neural pathways, and brain plasticity, will facilitate application of nutrition to optimize brain function and prevent as well as treat neurologic disorders.
The commonly used terms “functional foods” and “nutraceuticals,” which imply use of nutritional agents for prophylactic or therapeutic applications, are relevant to disturbances of the nervous system as well. General nutritional disorders can also occur in critically ill neurologic patients and require attention during management of these patients.
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