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There are loads of factors that play a role in the amount of food we eat, from portion size and price to accessibility and sales promotions. Individual sensitivity to these environmental factors — as well as a personal level of impulsivity — will determine the extent to which our food consumption habits are affected.

A recent study sought to determine the exact effect that sales promotions had on the impulsivity of snack food purchases in a supermarket. The 2013 study, led by Chantal Nederkoorn, questioned 118 participants regarding their gender, age, height, weight, family income, education, and level of hunger. It then tested them on their food purchases via an internet supermarket task.

Participants had to imagine that they were about to spend a three-day solitary weekend in a holiday house and they had to purchase everything they planned on eating or drinking over the three days. Some participants were randomly assigned to a version of the online supermarket that had sales promotions while others were assigned to one without. Prices were equal and the researchers sought to see how much of a participant’s purchasing decision was determined by the power of the online promotion.

Of the total participants, 45 were overweight and 73 were of healthy body weight. Impulsive participants bought more calories from snack products when they were advertised, but only when they were overweight. Those who were of normal body weight were affected very little by the sales promotion regardless of their level of impulsivity.

The bottom line is that impulsivity did not make all participants more likely to purchase promoted snack items — the lean impulsive participants were able to resist the urge while overweight participants were much more likely to exhibit worse levels of self-control.