A study of relationships of serum glucose, insulin, free fatty acids, and free and total tryptophan to mental illness.

To explore possible disturbances of cerebral monoamines linked to glucose metabolism, 18 schizophrenics, 21 neurotics, and 21 controls were given a 5-hr glucose tolerance test, and the effect of the glucose load on total and free tryptophan, insulin, and free fatty acids in serum was studied in medication-free patients. The data indicated intragroup differences (fasting to subsequent hours) in serum glucose, insulin, free fatty acids, and free and total tryptophan values. Intergroup differences were noted in insulin values at the first hour, in free fatty acids at fasting with neurotics exhibiting the highest values, and in free tryptophan at fasting with schizophrenics having the lowest values. Schizophrenics with perceptual disturbances (e.g., hallucinations) exhibited lower free tryptophan values when compared with other schizophrenics. The results indicated a glucose-tryptophan interaction in schizophrenics.