Stress triggers an increase in cortisone, a hormone that keeps the body ready to fight or flight. The persistence of stress and cortisone reduces the level of BDNF (brain-derived neurotrophic factor) and might cause the reduction of hippocampus.
An atrophy of hippocampus - amongst others, in turn, is related to chronic depression. Studies identify a link between the low level of BDNF and depression.
Exercise is generating an increase in BDNF, and consequently has a positive influence over depression.
More, a reduced level of BDNF is associated with an increased appetite, which might lead to obesity.
Today's formula:
exercise => increase in BDNF => 1. less depressive episodes
2. reduces appetite => less risk for obesity
Reference:
2. an interesting point of view: