Unfortunately, I don't know the incidence of depression in hunter gatherers.
If their incidence is very low (as it is for most Western diseases), then
diet might be important- as well as lead poisoning, etc etc.

Don't try to trivialise depression- it's a common and severe illness, and is
the main cause of suicide- which is a common cause of youth death. If you
don't like your doctor's attitude, try to find one whose attitude you do
like. Of course, depression often gets better by itself but this may take 1
or 2 years, by which time people's lives have changed drastically- they've
lost a lot of friends and soured relationships with the family. it can take
years to build it back up again- if ever. As they say, you can lose your
frineds but you cna't lose your enemies.

Naturally, diet and exercise are good for people with most illnesses.

Ben Balzer