Canadian scientists have challenged the common perception of a link between obesity and depression, finding an "obesity gene" is also a "happy gene".
Researchers at McMaster University have uncovered that the gene FTO - which is a major genetic contributor to obesity - is also associated with a reduction in the risk of depression.
The researchers said the discovery challenges the common perception of a reciprocal link between depression and obesity: That obese people become depressed because of their appearance and social and economic discrimination
It also challenges the idea that depressed individuals may lead less active lifestyles and change eating habits to cope with depression, which in turn causes them to become obese.
"We set out to follow a different path, starting from the hypothesis that both depression and obesity deal with brain activity. We hypothesised that obesity genes may be linked to depression," said senior author David Meyre, associate professor in clinical epidemiology and biostatistics at the Michael G DeGroote School of Medicine.
The researchers analysed 17,200 DNA samples from participants in 21 countries, and found the previously identified obesity predisposing genetic variant in FTO was also associated with an 8 per cent reduction in the risk of depression.
The finding was backed up by analysing the genetic status of patients in three additional large international studies.
The study has been published in the scientific journal Molecular Psychiatry.
"The difference of eight per cent is modest and it won't make a big difference in the day-to-day care of patients," Meyre said. "But, we have discovered a novel molecular basis for depression."
Meyre said the study is the "first evidence" that an FTO obesity gene is associated with protection against major depression, independent of its effect on body mass index.