It's the psychological impact of being overweight that is causing the depression, rather than any physiological problems associated with obesity, say researchers from the University of South Australia.
And it seems to affect women more than men, say the researchers who profiled around 48,000 people with depression against 290,000 healthy people and their medical and genetic data.
Genes that were associated with depression were also linked to obesity and a high BMI (body-mass index) score. "This suggests that being overweight causes depression—particularly in women," said Elina Hypponen, one of the researchers.
Paradoxically, the researchers saw similar links in men who are very thin, a group that is also more prone to depression than people of normal weight.