The psychological effects of diet induced lowered tryptophan in normal human males /

Biochemical theories postulate that deficient serotonergic functioning may be etiologically related to affective illness and aggressive behavior. In Study I mood and aggressivity were measured in thirty-six normal male subjects before and after ingestion of a Tryptophan Depleted, Tryptophan Loaded or Balanced amino acid mixture. While no differences in aggressivity were found, the Tryptophan Depleted group scored significantly higher at posttest on the MAACL Depression Scale than the control groups and demonstrated selective attention for dysphoric themes. In Study II a Balanced or Tryptophan Depleted amino acid mixture was administered to eighty normal male subjects prior to placing them in either a positive or negative environment, with or without instructions concerning the potential amino acid effects. The tryptophan depleted group became significantly more depressed than the control group regardless of environmental condition or instructional set. These findings suggest that lowered tryptophan may result in a central serotonergic dysfunction which is causally related to depressive affect and possibly to the pathogenesis of clinical forms of depression