Ever since Falstaff, fatness has been associated with jollity. According to psychologists at Lakehead University in Canada, the "jolly fat" hypothesis might actually be true, at least among women. Not only have they found a link, they suggest a mechanism, too: oestrogen.

They put forward the idea that body fat protects women again negative moods. In other words, the fatter a woman is, the less depressed she gets.

In the two-part research, the team looked at Body Mass Index (BMI), a measure that takes into account both weight and height, and compared it with mood in a group of young women. They found that the higher the BMI and body size, the lower the number of symptoms of depression, anxiety and negative mood. In fact, the most depressed were all thin, while the largest were the least miserable.

For explanations, the psychologists turned to biochemical research that suggested the possibility of a link between oestrogen and mood, and the brain chemical, serotonin, the target of widely used antidepressant drugs. They say very potent oestrogens are primarily found in fatty tissues, suggesting that women with higher body weight may have higher levels.