Recent research could not establish any connection between the serotonin system and depression. The serotonin system, has been a favoured area of research as it has a major effect on mood. However, its role in depression has not been able to be established in this recent significant genetic study. It seems that in this study that being overweight is more likely to increase the chance that you will be depressed.
“New techniques for identifying the genetic roots of disease have led researchers to conclude that 25 years worth of research studying a set of genes thought to be strongly associated with depression is wrong, according to a recent study in the American Journal of Psychiatry.”
To be honest, this doesn’t overly surprise me.