> here’s many possible factors in the past 100 years which could contribute to our poor mental health

Some more examples: breaking down of social contracts especially around family structures and religion, greater mobility meaning people lose contact with family and friends, greater isolation due to increased internet and tv usage, increased loneliness in many age groups, social media, greater access to depressing news (reddit in particular is a massive fountain of depression), a focus in modern western media on violence and violent heros, increased over sexualization which leads to fewer genuinely supportive sexual relationships for many people, and on and on.

I do think diet may play a role for some people. But I've personally been struggling with a deep depression over the past year (I think I'm over the worst now but it's been rough) and my diet is very healthy, low carb. I get plenty of exercise - could improve a bit but I'm probably top 5% for my age and gender. I don't sleep well when depressed, that's a big slippery slope. But I don't think fixing diets will be a magic bullet (although a society wide shift to healthier diets would have massive benefits in many areas).

The things that have genuinely helped me:

* CBT therapy (self taught). So called bibliotherapy I guess. Books by Beck and Seligman were especially helpful

* The book on male depression by Terence Real, especially the idea of covert depression that can hide for years behind addictions, or workaholism, or chasing status, etc. until that is lost for some reason and "real" depression appears. So many of the examples in that book resonated with me.

* Taking time off work

* Journaling daily

* Meditation and relaxation practice

* Deep and often painful conversations with my partner

* Socializing as much as possible but being careful to "fake it" and stay positive while doing so. After a few attempts I decided not to tell nearly anyone about my struggles

Things that didn't help me, or at least were ambivalent

* Keto diet for a few weeks. I feel it might have helped a bit but not hugely, and it was too hard for me to keep up. Going from a very unhealthy diet to a healthy diet would probably have a big benefit though

* Reaching out to friends and family - it's a sad truism that as a man, reaching out to people rarely works and is more likely to result in further isolation. If you do reach out, choose the people with great care. Accept when they don't respond well with feeling hard done by. Society has conditioned all of us to be hard on men who share. You might be more lucky than I was - it really depends on your friends I guess. Pre-covid I lived on the other side of the world and might have had better luck with my friends there. In any case, as per CBT therapy, it may even be more effective to go out and ignore your depression for a while and have a good time anyway

* Xanax - it did help me through a few rough nights but each time I paid back by feeling super anxious a day later so I don't take it much. I don't drink much but alcohol similarly

Didn't try but would if going through this again:

* Therapy, but only with a CBT (or similar) trained therapist

* Antidepressants, but only one of the non-anticholinergic ones, preferably something fast acting, and only with the clear intension to use it for a short time (3-6 months)