Herd behaviour

«Most of us are affected by the eating habits of our eating companions, whatever their intentions. As we have said, obesity is contagious; you’re more likely to be overweight if you have a lot of overweight friends. An especially good way to gain weight is to have dinner with other people. On average, those who eat with one other person eat about 35 percent more than they do when they eat alone; members of a group of four eat about 75 percent more; those in groups of seven or more eat 96 percent more*.

We are also greatly influenced by consumption norms within the relevant group. A light eater eats much more in a group of heavy eaters. A heavy eater will show more restraint in a light-eating group. The group average thus exerts a significant influence. But there are gender differences as well. Women often eat less on dates; men tend to eat a lot more, apparently with the belief that women are impressed by a lot of manly eating. (Note to men: they aren’t.) So if you want to lose some weight, look for a thin colleague to go to lunch with (and don’t finish the food on her plate).

*A colleague who raises chickens tells us that they behave the same way. A chicken who has already eaten enough to feel sated will start eating again if a hungry chicken is brought into the next cage.»

Nudge, Richard Thaler e Cass Sunstein