It sounds as though they may plan to help you improve your nutritional condition, thereby isolating/removing nutritional impacts, then re-evaluate. It may be like peeling an onion, as more than one thing may be having an impact.

It sounds like a good start. Wishing you all the best.

BTW, the connection between eating and disposition has been discussed in multiple threads over the years. Here is a recent summary of the acronym HALT, and a few other related words.