Depression is a multifactorial psychiatric illness. It is a mix of genetics, trauma, chronic stress, loneliness, medical illness, pain, hormones, inflammation, cognitive style (rumination, negative bias), and lifestyle factors.
Poor people may have depression.
Rich people may have depression.
Physically healthy people may have depression.
Medically ill people may have depression.
Athletes may have depression.
People with a sedentary lifestyle may have depression.
Obese people may have depression.
Fit people may have depression.
So, in short, depression is not a lifestyle disease.
And from when anatomy doctors started commenting on Psychiatric,endocrine and gynaecology disorders?