Malnutrition can cause vitamin-deficiency-related diseases like scurvy and rickets. As malnutrition worsens, those affected have less energy and experience impairment in brain functions. This can make it difficult (or impossible) for them to perform the tasks needed to acquire food, earn an income, or gain an education. Malnutrition can also cause acute problems, like hypoglycemia (low blood sugar). This condition can cause lethargy, limpness, seizures, and loss of consciousness. Children are particularly at risk and can become hypoglycemic after 4 to 6 hours without food. Dehydration can also occur in malnourished people, and can be life-threatening, especially in babies and small children. Signs
There are many different signs of dehydration in malnourished people. These can include sunken eyes; a very dry mouth; decreased urine output and/or dark urine; increased heart rate with decreasing blood pressure; and altered mental status. Cognitive development
Protein-calorie malnutrition can cause cognitive impairments. This most commonly occurs in people who were malnourished during a "critical period ... from the final third of gestation to the first 2 years of life". For example, in children under two years of age, iron deficiency anemia is likely to affect brain function acutely, and probably also chronically. Similarly, folate deficiency has been linked to neural tube defects.Iodine deficiency is "the most common preventable cause of mental impairment worldwide." "Even moderate [iodine] deficiency, especially in pregnant women and infants, lowers intelligence by 10 to 15 I.Q. points, shaving incalculable potential off a nations development."
For example, prion diseases, all of which cause transmissible spongiform encephalopathies, are invariably fatal, but other encephalopathies are reversible and can have a number of causes including nutritional deficiencies and toxins. See also
Brain damage
Neuroscience
Neurological disorder
Psychoorganic syndrome

References
Adapted from: Office of Communications and Public Liaison (9 November 2010). "NINDS Encephalopathy Information Page". National Institute of Neurological Disorders and Stroke, National Institutes of Health. Archived from the original on 2009-03-23. Retrieved 2005-09-01. Further reading
The Diagnosis of Stupor and Coma by Plum and Posner, ISBN 0-19-513898-8, remains one of the best detailed observational references to the condition.