New research has found that being depressed increases the impact of having a genetic predisposition for obesity.

A team based at the University of Edinburgh analyzed data from thousands of Scottish adults to see whether they had genetic mutations either linked with obesity or major depressive disorder. They tested for relationships between those genetic profiles, the presence of depression or other psychological distress, and body mass index, a measure used to determine obesity. A genetic predisposition for obesity more strongly predicted actual obesity among those adults who were also depressed.

The findings were reported June 30th in Translational Psychiatry by a team including 2008 NARSAD Distinguished Investigator Grantee David J. Porteous, Ph.D., and 2010 Independent Investigator Andrew M. McIntosh, Ph.D.

The study results show people becoming obese in part because of their depression, rather than becoming depressed because they are already obese. The experience of depression may drive disordered eating habits. It may also trigger chemical responses in the body (such as the release of the stress hormone cortisol) that promote weight gain, the researchers hypothesize.

The team also found some degree of association between a genetic profile linked to obesity and current psychological distress, even among individuals who were not obese. Obesity-linked genes also more closely predicted actual obesity among people experiencing distress even if they were not diagnosed with depression. This indicates that psychological strain, and not just depression per se, contributes to obesity.

One limitation of this study is that the researchers had much less data to develop a clear genetic profile of depression compared to their genetic profile of obesity. More research is needed to see whether a genetic predisposition for depression, if more firmly established in the coming years, can be related to weight gain, even in people who do not report symptoms of depression.

Read the abstract.