I know first-hand that low energy-levels and lacking energy production mechanically lead to depression.
Also, look at how people (children also) experience the world and their relationships and their stresses when they are tired (or even just hungry) compared to when they are fit...
Fix those, and the depression might be gone.
This is not bashing against anti-depressants, they play their role to. But in some cases, energy-management is key.