[thisiswater]

Part of the problem here is the vagueness of the term. Sometimes, diagnosing someone with "depression" is like diagnosing them with a headache - accurate, but not particularly clinically useful.

Lifestyle changes will help some depression, it will not help others. Generalizing from your own experiences is useful, but be very careful with how you present this to others.

Telling a chronically depressed person they just need to take a walk and eat some fruit is not just insulting, it's fodder for self-invalidating thoughts which can increase self-destructiveness.