There is a report that the amino acid glutamine caused psychiatric symptoms, including depression, temporarily in patients. This was reported in a recent American psychiatric textbook. Pauling discussed a similar situation with the amino acid phenylalanine in the disease PKU.

In certain types of avitaminosis there are mental symptoms. One example is a deficiency of niacin, which is required in glycolysis. Glycolysis is critical to brain energy metabolism. This subject was reviewed by Dr. Abram Hoffer.