A cross-sectional design is totally inappropriate for this type of question. The results are almost certainly driven by selection bias: i.e. depressed people behave differently. 

Without seeing changes from before and after the dietary change, you basically can’t learn anything. 

TLDR; nutrition research is almost always done poorly. 

I'm not really the right one to answer that. But my general take is a varied diet is probably your best bet. Just keep in mind that everyone's unique, so what clicks for some might not for others.

0xbitcoiner

HealthAndFitness

Mental health consequences of dietary restriction

So is it recommended or not to go carnivore or to do fasting?