Obesity and depression often go hand in hand. Weight gain makes people bad about themselves. Depressed people tend to not take care of themselves as well. It becomes a circular situation of overeating and feeling sad.
Research by Sarah Markowitz, MS shows how closely obesity and depression are linked. She also suggests, however, that these conditions can be treated together. Exercising more and reducing stress are two things you can do starting now to improve both conditions.
Dieting to lose weight has a bad effect on depression and many antidepressants actually cause weight gain though. It's important to be careful when devising a treatment plan. You doctor, however, can prescribe something to treat the obesity and depression without worsening either condition.