We developed a novel experimental procedure called the ‘precommit-to-eat’ paradigm to test how stress impacts precommitment. Participants, who reported trying to eat healthily in their everyday lives, came to the lab twice: once when they were placed under acute stress and once when they were in a non-stressful control condition. In each session, they completed two tasks in which they made choices about pairs of food items. In each pair, one food item had been rated as tastier but less healthy (e.g. chocolate muffin) than the other item (e.g. banana).
In the first task, participants were presented with the pairs of food items. For half of the pairs (viewing trials), participants simply observed the food items. However, for the other half of pairs (precommitment trials), participants could remove the tastier but unhealthier food item (e.g. the chocolate muffin) from their future choice, thereby limiting their later options (e.g. only the banana remained available). The number of unhealthier items participants removed indicated the extent of precommitment – that is, how much they restricted their future choice set.
In the second task, participants chose which food items they would like to eat at the end of the experiment from the same food pairs they had seen in the first task. If participants had removed the unhealthier item in the first task, then they were compelled to select the healthier item in this pair in the second task. This allowed a direct comparison between choices made with and without the opportunity for prior precommitment. We also collected salivary cortisol and measures of participants’ psychological stress throughout the experiment to assess stress responses.
We found that the opportunity to precommit – the chance to remove the unhealthier food items – increased the selection of healthier food items by over 40%. When participants felt more stressed, they were more likely to pick the unhealthier food items to eat in the second task, but only when they had not previously had the chance to precommit. When given the chance to precommit in the first task, participants who felt stressed made healthier choices in the second task at the same rate as those who did not feel stressed. Further analysis showed that increased feelings of stress were associated with more precommitment in the first task.
This shows that when behavioural strategies, such as precommitment, are available, stress can prompt greater use of these strategies. The results show that precommitment is an effective self-control strategy for maintaining healthier choices under stress.
