Re-analysis of a meta-analysis about tryptophan and depression

This is a reanalysis of a meta-analysis about L-tryptophan blood levels and depression, which became part of the controversy around a recent umbrella review about the role of serotonin in depression. The reanalysis revealed major methodological limitations, raising doubts on the conclusions in the original publication that levels of tryptophan are lowered among depressed compared to non-depressed individuals. The data is also compatible with a null effect and no firm conclusion should be made.