Food Menu Labelling Effects on Individuals With Eating Disorders and Other Mental Health Conditions.

An adapted version of the University of North Carolina Perceived Message Effectiveness (PME) scale will be used as a measurement of how effective participants believe nutritional labelling is in promoting behaviour change. The scale measures health concern, product attitude, and discouragement of item consumption in response to public health messaging or in this context, the food menu presented during the study. Participants will be shown a screenshot of the menu they ordered. All participants will answer 3 questions using a Likert scale ranging from 1 - 5 anchored by "Strongly disagree" and "Strongly agree". The mean response to the three items will be calculated. PME is used as an early indicator of a health messages potential to change behaviour (e.g., reduce selection of less healthy items). The scale has been used previously to identify the potential impact of food labels and is predictive of long-term behaviour.

Participants will be asked 'To what extent was the menu useful in helping you identify healthy vs. less healthy food choices'. Participants will select their answer on a Likert scale ranging from 1 - 5 anchored by "Strongly disagree" and "Strongly agree".

An overall measure of nutritional quality of participants food order will be calculated using mean UK NPM scores of individual items, weighted according to the energy content of the item. Nutritional content used to calculate NPM scores for each menu item was obtained from outlet websites and input into the online NPM calculation tool (2004/05). Weighted scores will be calculated using the weighted.mean function in R.

Participants will complete an adapted version of PANAS after completing the food selection task. This is a 20-item measure, whereby participants will be asked to 'indicate the extent you feel this way right now' on a scale of 1 to 5 from 'very slightly or not at all' to 'extremely'. Participants receive a positive affect score and a negative affect score.

Questions were developed based on self-reported mental health-related outcomes in previous research. Participants will be asked to respond to each of the following points on a scale of 1 to 5 from 'very slightly or not at all' to 'extremely'.

The information on the menus made me feel...

• Anxious about my food choice
• Guilty about my food choice
• Reassured about my food choice
• Ashamed about my food choice
• Fixated on the nutritional content of my food choice

Two additional questions relating to compensation were adapted from an existing scale related to compensatory eating behaviour and alcohol (CEBRACS). Participants will be asked to respond to each of the following points on a scale of 1 to 5 from 'very slightly or not at all' to 'extremely'.

• Like I should eat less than usual during one or more meals to make up for the amount of food I have selected
• Like I should skip one or more meals to make up for the amount of food I have selected

We will record the Nutri-Score values (A-E) of all items selected by participants in the food choice task. Participants will be coded as having ordered any of the healthiest menu items labelled A or B (Y/N) and/or the least healthy menu items labelled D or E (Y/N).

We will record the energy and nutrient content of all items selected by participants in the food choice task. The total energy content of the ordered meal will be calculated.

Participants will be asked to report their highest level of education achieved:

• Less than high school
• High school completion
• College or foundation degree
• Bachelor's degree
• Master's degree

Participants will be asked several questions to assess whether they noticed any nutritional labelling, and if the labelling impacted their food choices. Questions will be amended slightly according to labelling condition.

Participants will report their age on a dropdown list

Participants will select their gender from the following options:

• Man
• Woman
• Non-binary
• Other
• Prefer not to say

Participants will select their ethnicity from a dropdown list:

White English/Welsh/Scottish/Northern Irish/British White Irish Any other White background White and Black Caribbean White and Black African Any other mixed/multiple ethnic background please describe Indian Pakistani Bangladeshi Chinese Other Asian African Caribbean Arab Any other ethnic group

Participants will report their height in either cm or ft and inches. This will be converted to metres in order to calculate BMI.

Participants will report their weight in either kg or stones and pounds. All will be converted if necessary to KG to calculate BMI.

Participants will be asked how often over the past year they have eaten food prepared out of the home (from restaurants, cafes, fast food etc.). The following options will be listed.

• Not in the last year
• Less than once per month
• 1-3 times per month
• 1-2 times per week
• 3 times per week or more