The effectiveness of a dietary challenge for improving dietary intake in Australian adults.

Part 1 of the study involved completing an initial screening survey. Participants were asked to complete a series of questions about their health behaviours (including dietary intake) and their readiness to change such behaviours. They were also asked several behavioural and psychological measures that formed predictors for participation in the intervention (the second phase of the study). Participants who met the criteria for sweet treat intake on more than 5 days per week were invited to participate in the second phase of the study. They were asked to contact the study team to indicate their interest and provide their initials and last 3 digits of their phone number to facilitate data matching. Those who contacted the team were sent a second information sheet and asked to indicate consent via email. Part 1 occurred within a couple of weeks of part 2. Part 2: The intervention itself was designed to be as straightforward as possible, with minimal participant commitment needed to initiate it. Participants were provided an online visual tile explaining the challenge aim. the message was “Try to eat less sweet snacks including biscuits, buns, cakes, muffins, doughnuts, lollies, and chocolate, for the next four weeks”. Participants were instructed to select any way that worked for them, but suggested tactics including reducing the frequency (i.e., cutting out all or some of these foods), reducing the portion size (i.e., amount eaten each time), having “sweet treat free days”, and making healthy swaps (e.g., fruit or low-fat yoghurt). No other support was provided to participants. Participants were instructed to reduce sweet treat intake for 4-weeks, but a specific amount was not indicated as any reduction in discretionary food intake is beneficial for working toward meeting the Australian Dietary Guidelines. Participants used an Ecological Momentary Assessment (EMA) smartphone application to record their sweet treat intake intake once daily as well as their mood twice daily. No other direct contact was made with the participants over the four weeks, other than to respond to enquiries and to send links to complete follow-up surveys (i.e,, start of challenge, week 2, week 4). A key outcome of the study involved validating the CSIRO behaviour change readiness index, which comprised psychological and experiential predictors of initial interest and committed intention to change a health behaviour, as well as behaviour change success. This will be done by assessing the utility of the index for predicting successful short-term behaviour change outcomes in the dietary domain (i.e., sweet treat intake), but also to better understand the associations and strengths of relevant factors to refine this tool into a succinct survey. Thus, the study focused on predicting behavioural outcomes rather than improving health behaviours. The validation of the index involved participants from part 1 of the study. We further refined this tool based on a previous study conducted in a different dietary domain (Assessing the effectiveness of a water intake challenge and the validity of a behaviour change readiness index for predicting beverage intake in Australian adults.).