Objective: It has been hypothesized that reduced dietary availability of tr
yptophan may be the cause of impaired serotonin activity in underweight ano
rexics. The study reported here evaluated the relationship between tryptoph
an availability in the blood and nutritional status in anorexia nervosa. Me
thods: The total amount of tryptophan and the ratio between tryptophan and
other large neutral amino acids (TRP/LNAA) were assessed in a sample of 16
starving anorexic patients. Body weight and composition and energy intake w
ere evaluated in all. patients. All subjects also completed self-reported q
uestionnaires such as the Hopkins Symptom Checklist and Eating Disorders In
ventory (EDI). Results: The TRP/LNAA ratio seems to be higher in patients w
ith a more severe catabolic status. It is, in fact, significantly inversely
correlated with body mass index, body fat, muscle mass, daily energy intak
e, and daily tryptophan intake. The TRP/LNAA ratio also correlates with gro
wth hormone and the EDI drive for thinness. Patients who exercise excessive
ly had significantly higher TRP/LNAA ratios. Conclusions: in starving anore
xic patients, the TRP/LNAA ratio does not seem to be determined by the cont
ent of tryptophan in the diet, but it correlates with measures of catabolis
m. The relationship of the TRP/LNAA ratio to excessive exercise and starvat
ion indicates the importance of further investigations exploring the role o
f tryptophan availability in maintaining anorexia nervosa.