The nature and persistence of the effects of posthypnotic suggestions on food preferences: The final report of an online study

Abstract

The persistence of food preferences, which are crucial for diet-related decisions, is a significant obstacle to changing unhealthy eating behavior. To overcome this obstacle, the current study investigates whether posthypnotic suggestions (PHSs) can enhance food-related decisions by measuring food choices and subjective ratings. After assessing hypnotic susceptibility in Session 1, at the beginning of Session 2, a PHS was delivered aiming to increase the desirability of healthy food items (e.g., vegetables and fruit). After the termination of hypnosis, a set of two tasks was administrated twice, once when the PHS was activated and once deactivated in counterbalanced order. The task set consisted of rating 170 pictures of food items, followed by an online supermarket where participants were instructed to select enough food from the same item pool for a fictitious week of quarantine. After 1 week, Session 3 mimicked Session 2 without renewed hypnosis induction to assess the persistence of the PHS effects. The Bayesian hierarchical modeling results indicate that the PHS increased preferences and choices of healthy food items without altering the influence of preferences in choices. In contrast, for unhealthy food items, not only both preferences and choices were decreased due to the PHS, but also their relationship was modified. That is, although choices became negatively biased against unhealthy items, preferences played a more dominant role in unhealthy choices when the PHS was activated. Importantly, all effects persisted over 1 week, qualitatively and quantitatively. Our results indicate that although the PHS affected healthy choices through resolve, i.e., preferred more and chosen more, unhealthy items were probably chosen less impulsively through effortful suppression. Together, besides the translational importance of the current results for helping the obesity epidemic in modern societies, our results contribute theoretically to the understanding of hypnosis and food choices.

Hypnosis in psychotherapy, psychosomatics and medicine. A brief overview

“…These studies confirm the dissociation theories of hypnosis. The changes in the brain caused by hypnosis have also been demonstrated using event-related brain potentials, e.g., for the most important sensory-affective phenomena such as analgesia (as a kind of negative kinesthetic hallucination) ( Miltner and Weiss, 2007 ; Franz et al, 2024 ), for negative acoustic ( Franz et al, 2020 ) and for negative visual ( Franz et al, 2021 ) hallucinations, as well as for purely cognitive phenomena such as post-hypnotic suggestions ( Zahedi et al, 2020 ; 2023b ).…”

Cognitive simulation along with neural adaptation explain effects of suggestions: a novel theoretical framework

“…Finally, (C) direct verbal suggestions can affect value-based decision-making via shifting preferences (Ludwig et al, 2014;Zahedi et al, 2020aZahedi et al, , 2023. For instance, by inducing preferences for healthy food items, posthypnotic suggestions can shift participants' choices toward healthy food and promote faster rejection of unhealthy items (Ludwig et al, 2014;Zahedi et al, 2020aZahedi et al, , 2023.…”

“…Second, in tasks where both disruption of bottom-up processes and improving top-down modulations can enhance performance (e.g., in the Stroop, Simon, and Flanker tasks), participants rely heavily on proactive cognitive control when suggestions are active, as measured by EEG band frequencies ( Zahedi et al, 2017 ), event-related potentials ( Zahedi et al, 2019 ), and pupillometry ( Parris et al, 2021 ). Finally, (C) direct verbal suggestions can affect value-based decision-making via shifting preferences ( Ludwig et al, 2014 ; Zahedi et al, 2020a , 2023 ). For instance, by inducing preferences for healthy food items, posthypnotic suggestions can shift participants’ choices toward healthy food and promote faster rejection of unhealthy items ( Ludwig et al, 2014 ; Zahedi et al, 2020a , 2023 ).…”

“…As mentioned above, direct verbal suggestions can be used to affect participants’ decisions. One interesting application of suggestions is related to shifting participants’ food choices toward more healthy food items ( Ludwig et al, 2014 ; Zahedi et al, 2020a , 2023 ). The suggestion that is used for this matter commonly asks participants to imagine a specific type of food and, by attending to its physical properties, imagine how delicious it is ( Zahedi et al, 2020a ).…”

“…Accordingly, previous studies show that direct verbal suggestions affect participants’ preferences for the targeted food items, which can explain changes in their choices ( Zahedi et al, 2023 ). Further, the changes in preferences are related to the increased P1 amplitude ( Zahedi et al, 2020a ), which is an early ERP component that has been shown to be associated with preferences and reward saliency ( Hickey et al, 2010 ; Donohue et al, 2016 ).…”