title: The effect of a nutritional source of tryptophan on dieting-induced changes in brain 5-HT function.
abstract: BACKGROUND
  Dieting in healthy women results in a decrease in the availability of tryptophan (TRP), the amino-acid precursor of serotonin (5-HT), for brain 5-HT synthesis. This is associated with increases in the prolactin response to 5-HT drug challenge suggesting a 'supersensitivity' of 5-HT neuroendocrine responses. The aim of the study was to assess whether increased TRP intake during dieting would prevent the changes in TRP availability and 5-HT neuroendocrine function.
  
  
  METHODS
  Fifty female subjects underwent a 1000 kcal daily diet for 3 weeks. In the final week of the diet subjects were randomly allocated to receive either nutritionally-sourced TRP (1.8 g daily) or placebo in a double-blind, parallel group, design.
  
  
  RESULTS
  TRP supplementation failed to modify the dieting-induced reduction in fasting TRP availability to the brain. However, in contrast to placebo-treated subjects, subjects receiving additional TRP did not show enhanced prolactin responses to intravenous TRP challenge.
  
  
  CONCLUSIONS
  The decrease in TRP availability produced by dieting may be due to increased TRP metabolism rather than decreased TRP intake. While TRP treatment did not increase fasting TRP availability it may have modified the effect of dieting on brain 5-HT function. Further studies will be needed to see if this effect of TRP has consequences for the effectiveness of dieting as means of weight control.
authors.affiliation: University Department of Psychiatry, Warneford Hospital, Oxford.
authors.forename: M J
authors.initials: MJ
authors.lastname: Attenburrow
authors.forename: C
authors.initials: C
authors.lastname: Williams
authors.forename: J
authors.initials: J
authors.lastname: Odontiadis
authors.forename: J
authors.initials: J
authors.lastname: Powell
authors.forename: F
authors.initials: F
authors.lastname: Van de Ouderaa
authors.forename: M
authors.initials: M
authors.lastname: Williams
authors.forename: P J
authors.initials: PJ
authors.lastname: Cowen
mesh_terms: D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D001921:Brain / Q000503:physiopathology; D004038:Diet, Reducing / Q000009:adverse effects*; D004311:Double-Blind Method; D002149:Energy Intake / Q000502:physiology; D005260:Female; D006801:Humans; D011208:Powders; D011388:Prolactin / Q000097:blood; D012701:Serotonin / Q000502:physiology; D014364:Tryptophan / Q000008:administration & dosage* / Q000097:blood / Q000172:deficiency*
chemical_list: D011208:Powders; D012701:Serotonin; D014364:Tryptophan; D011388:Prolactin