Plasma tryptophan and anorexia in human cancer

A correlation between anorexia and brain levels of serotonin and tryptophan (TRP) has been reported in tumor-bearing animals. In the present investigation 45 patients with various types of cancer and 13 control subjects were studied. Prior to the study the patients had received no antineoplastic therapy and were unaware of the malignancy of their disease. Feeding behavior was investigated by means of a questionnaire in which the presence of anorexia (A), aversion to meat (MA), taste (TA) or smell (SA) alterations, nausea and/or vomiting (NV) and early satiety (ES) was assessed. Plasma levels of free TRP, the other neutral amino acids (NAA), albumin and non-esterified fatty acids (NEFA) were assayed. Plasma-free TRP was significantly increased in anorectic cancer patients. The free TRP/competing NAA ratio, which might better predict brain TRP levels, was significantly higher in patients with A, MA, TA, SA, NV and ES than in controls or in non-anorectic (NA) cancer patients. These findings seem to confirm that free TRP may play an important role in human cancer anorexia.