Melbourne School of Psychological Sciences - Theses
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ItemInvestigating the influence of food product health warnings on dietary decisions using survey, behavioural and neural evidence( 2018)The sharp increase in obesity rates seen globally over the past five decades has necessitated the introduction of new health intervention approaches for promoting healthier dietary behaviour. The application of health warning messages to product packaging is now a successful component of tobacco control policy in over 300 countries, and recent proposals have argued that a similar approach might assist in reducing the impact of obesity and diet-related disease. However, there is currently limited empirical support for the use of health warnings in this context. The primary aim of the present thesis was to investigate whether health warnings are effective in promoting healthier dietary behaviour. A combination of survey, behavioural and electroencephalography (EEG) data are presented here to study this question and supplementary questions concerning the psychological and neural mechanisms through which health warnings influence intentional and automatic behaviours, and the design characteristics of health warnings that optimise their efficacy. In Study 1, two survey-based experiments sought to validate health warning stimuli for use throughout the thesis, and to examine how health warning design characteristics (positive or negative message framing, text-only versus text-and- graphic warnings) influence perceived efficacy and behaviourally relevant cognitive and affective responses to these stimuli. Health warning message topics that were perceived to be effective for influencing dietary behaviour were selected for use in subsequent experiments. The results indicated that health warnings featuring negatively framed messages accompanied by graphic imagery were perceived as most effective and evoked the strongest negative emotional responses. This pattern of results is consistent with prominent theories of behaviour change contending that health communication messages promote behaviour change intentions by increasing the perceived threat associated with unhealthy behaviours. Study 2 was conducted to identify appropriate snack food stimuli for use in subsequent behavioural and EEG experiments measuring the influence of health warnings on dietary self-control. Participants rated images of snack food stimuli on scales measuring food attributes that have been shown to motivate dietary choices. A set of snack food stimuli that spanned the full range of perceived health and taste attributes was selected. This was necessary, as health-related dietary self-control involves trading off the short-term hedonic rewards associated with eating tasty food against the expected long-term health consequences associated with eating unhealthy foods. Studies 3 and 4 aimed to test whether health warnings were capable of improving dietary self-control by priming healthy eating goals as food choices were made. Study 3 employed a behavioural paradigm in which fasted participants first provided subjective health and taste ratings for the food items selected in Study 2 and then, in two decision stages, indicated whether they would like to eat these foods at the end of the experiment. Between the two decision stages, participants were randomly assigned to one of four health warning conditions (one for each of the health warning design characteristics) and exposed to health warning stimuli, or to non-message stimuli in a control group. A measure of dietary self-control captured the propensity for participants to select healthy but not tasty items or to reject unhealthy but tasty items. Health warning group participants displayed improved dietary self- control following exposure to the intervention, with the negatively framed graphic warning group improving the most, while control groups participants displayed no change. Study 4 analysed EEG data measured while viewing food stimuli during the decision stages of the paradigm used in Study 3, in order to investigate the influence of health warnings on neural measures of food cue reactivity that have been related to dietary choice behaviour. Analysis of event-related potential (ERP) data revealed that early sensory attention, indexed by the N1, was modulated in accordance with the perceived health qualities of food stimuli but that this modulation was not influenced by health warning exposure. However, health warning exposure attenuated the amplitudes of the P3 and late positive potential in response to palatable food stimuli. These components of the ERP are thought to index the deployment of motivated attention in accordance with current decision goals. The results of Studies 3 and 4 supported the hypothesis that health warnings are capable of priming health goals, reducing automatic appetitive responses to food stimuli, and promoting healthier dietary behaviour. Overall, these findings indicate that food product health warnings, particularly those featuring graphic imagery and presented using a negative message frame, have the potential to promote healthier dietary behaviour by increasing intentions to eat healthily, and by priming these intentions at the crucial moment of dietary decision making, counteracting the appetitive influence of environmental food cues.