New evidence in economics and epidemiology seems to suggest that we care about other people’s weight as much as we do our own. It’s always more desirable to be slim – perhaps because it offers a better chance of finding a person to date or marry, or even faster job promotion. However, when the people we normally compare ourselves with become fatter, the cost of putting on weight for many of us reduces. Put simply, when other people around me become fatter, I don’t have to compete so much with them to stay slim.

According to research conducted by economists David G. Blanchflower, Andrew Oswald and Bert Van Landeghem, people with weight problems – those with a body mass index (BMI) of 30 or over – are significantly unhappier than people within a healthy weight range (BMI 18.5–25). However, the overweight tend to report higher levels of happiness when other people of the same age and gender are as heavy or heavier than they are. The same also goes for individuals who live in the same household: our own weight doesn’t bother us as much, that is, when our partner is also putting on weight.

This positive relationship between our happiness and other people’s weight provides a good psychological explanation for the current obesity epidemic in the west. It’s psychologically easier for us to accept being overweight when everyone else is also overweight – assuming, of course, that most of us enjoy food a lot more than dieting.