having cured my own depression, it can be both circumstantial and hormonal (chemical) imo.

lacking nutrients is a catch 22 in mental health, you feel shit so end up eating shit and spiral down.

i changed my diet to keto and my depression reduced enough for me to get my life somewhat back on track.

recent studies in glycine is showing to be rather a good mood enhancer and i can personally say even though i havnt had depression in a few years now i have found im generally happier since i started taking it four weeks a go.