In Medicine you rightly need some very expensive 'gold standard' double-blinded placebo-controlled trials published in influential journals before any new treatment is considered both safe and effective. The expense of these trials tends to become exponential to the number of variables (vitamins, minerals, and amino acids) to be controlled for. This is a major problem in bespoke treatments with multiple supplements tailored according to individual testing such as in this paradigm. Getting funding is a major issue when there isn't a patent involved it seems.
Because of this funding problem, as older studies have become deprecated over time, more recent publications have been perforce limited to piecemeal pilot studies for aspects of the paradigm and one comprehensive outcome study. Pilot studies are those which are able to demonstrate promise and the need for further research funding, but they are not the 'gold standard'. They also tend not to be published in journals with wide readership. It bears repeating that funding seems to be a problem when the prospect of lucrative patents is not present.
There is also the widespread perception of the superior efficacy of pharmaceutical interventions which do not suffer this funding, publishing, and marketing disadvantage. When trying to get interest in this therapy Dr Walsh reports the common question is "Don't you really need a powerful drug to get the job done if you got a person who's got a serious problem like suicidal depression or schizophrenia?" and not many are open to the possibility other approaches may be helpful with less side-effects.
There is hope this may change for the sake of those afflicted and efforts are progressing in academic research towards this.