You’re feeling full but here’s the waiter with the dessert menu. You’re about to say “No thanks” when your friend orders baked cheesecake. And soon you’re saying: “I’ll have one too, thanks.” Studies repeatedly show that what we eat is highly influenced by who we eat with. The most recent research, presented at last week’s American Heart Association meeting, found that the chance of a “diet lapse” was 60% when eating with others. The research followed 150 people trying to lose weight or keep weight off, for a year, using phones and an app to capture what and where they ate. Those in the study were asked to limit their calories. They were most successful in keeping to their diet when they ate alone. Work, with its temptations of cake for somebody’s birthday, led to a 40% chance of a diet lapse. The car was the safest place, with only a 30% chance of overeating.

But it’s annoying that dining with family or friends could make us eat more. A study of 63 adults who kept seven-day dairies found that eating with people increased meal sizes by 44% and participants ate more fat than when they ate alone. The lead researcher, US physiologist John de Castro, suggested that eating alone would reduce caloric intake and improve diets. In another study he showed that meals eaten with spouses and family had more calories and were eaten faster, while those with friends were as large but lasted longer. This was true for all meals of the day, and if men were at the table, women tended to eat more than usual. So although eating with friends or family is one of the joys of life, if you want to watch your weight, should you eat on your own?

The solution

We seem to be compelled to model how we eat on those around us; not only on what they eat but on how big they are. A study in the journal Appetite showed that in the presence of an actor in a convincing fat suit, people in a restaurant ate 31.6% more pasta, whatever she ordered. If she ordered salad, they served themselves 43.5% less salad. Another study, in the New England Journal of Medicine, found that if a close friend became obese, his or her pal had a 171% increased risk of doing so. Somehow we aren’t good at self-regulating what we eat. We copy others. What we should do is concentrate on ourselves a bit more. If eating out, see the menu online before and plan your meal. Don’t just opt for what “she is having”. Better still, do as dietician Aisling Pigott says: “We forget to value and enjoy food. Don’t restrict and binge. Listen to your body’s needs.” So ignore what others are eating, especially if they are in a fat suit.