Improving the diet quality: "My Nutrition Score" of Australian adults using a brief, online, tailored, nutrition messaging intervention: A Randomised Controlled Trial with a nested Cross-Over Trial study design

Name: Group 1 (intervention: tailored message group) Why: The use of message framing as an influential communication strategy has been successful in promoting health related behaviours such as lowering alcohol consumption and reducing smoking. However, the same success has not always been achieved for eating behaviours. What: Participants will be invited and randomised to intervention or control group. A baseline online questionnaire will measure: intention to reduce discretionary choice intake; diet quality using a validated Short Food Survey; and positive diet-behaviour enablers. The cross-over trial will test differences in Group 1 participants’ reported intention to eat less discretionary choices following exposure to 4 different evidence-based nutrition messages. The cross-over trial will occur at one time-point, at baseline. The messages will be standard within each frame, and provided as text. They will be framed as follows: • Gain framed nutrition message (53 words) • Loss framed nutrition message (53 words) • Majority social norm framed nutrition message (37 words) • Minority social norm framed nutrition message (40 words) How: Participants will receive the messages in a random order with washouts lasting for a minimum of 30 seconds each. Following each message, participants will report their intention to change their discretionary food intake, and the nutrition message with the highest intention for change will be the one that is taken forward as part of the individual’s tailored nutrition intervention. Where, when, how much: Based on the highest intention-to-change score following the message exposures in the cross-over trial, Group 1 participants will receive this message (the one resulting in the highest intention score) as their tailored intervention, via two emails at baseline and Week 2 of the study, each approximately comprising 500 words. These emails will encourage the new behaviour: eat less discretionary choices, using tailored and instructional messages to support the reduction of discretionary choices, guided by the Behaviour Change Wheel ‘COM-B’ framework. The tailoring approach will be utilised as evidence shows that, in comparison to general messages, more specific and tailored instruction may increase engagement in a behaviour change intervention. 4 weeks after baseline, all participants will receive an email with links to complete follow-up surveys. Group 1 will be asked to complete a follow-up questionnaire at Week 4 (from baseline) to measure: follow-up intention and diet quality. Planned fidelity: In the follow-up questionnaire, participants will be asked if and how often intervention emails were read.