Study designs of evaluations included in the review
Within-subject, placebo-controlled studies were eligible for inclusion. All of the included studies were of a
placebo-controlled, double-blind crossover design and treatment order was balanced over test days.
Specific interventions included in the review
Studies that assessed the effects of ATD using an amino acid mixture as treatment were eligible for inclusion. All of the included studies compared a mixture of 15 amino acids (range: 52 to 100 g; the ATD-inducing treatment) with the same 15 amino acids plus between 1.15 and 4.6 g L-tryptophan (TRP; used as placebo treatment). All of the studies appeared to use one dose of treatment.
Participants included in the review
The authors did not report any criteria for inclusion. Where reported, the studies included healthy controls and participants with a family history of depression, or who had recovered from depression, or had irritable bowel syndrome. The mean age ranged from 21.8 to 77.0 years.
Outcomes assessed in the review
Studies using a word-list learning test as a measure of declarative memory were eligible for inclusion. All studies reported on the visual verbal learning test (with 15 or 30 words in the list); immediate recall, delayed recall and delayed recognition were reported. Depression and blood or plasma levels of tryptophan and TRP were also assessed.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.