Supermarket Labelling and Taxation Study

Nutritional quality of food order

The nutritional quality of the participant's full food order will be calculated using mean-weighted UK Nutrient Profiling Model (NPM) scores (32). NPM scores are calculated by subtracting the total value of positive nutrients (fruit, vegetables \& nuts, fibre, protein) from the total value of negative nutrients (calories, saturated fat, sugar, salt). Lower scores indicate better nutritional quality. To account for multiple items being selected, we will calculate a mean NPM score, weighted by the energy content of individual food items. This will be done using the 'weighted.mean' function in R (33) grouped by participant so the weights are specific to individual orders.

Likelihood of purchasing a less healthy option

Any participants who select a less healthy item (high in at least one nutrient/energy) as part of their meal will be coded as 1, and participants who have only selected options that are not 'high in' will be coded as 0.

Number of additional items purchased

Determined based on the total number of additional items (other than the main ready meal) selected in the food choice task. Participants may choose fewer items in response to labelling/taxation.

Total energy and other nutrient intake

Determined based on the total calorie, saturated fat, salt, and sugar content of all items in the Tesco order and an estimation of the proportion of each item that was consumed. Participants will take a photograph of each ordered food item before (i.e., when it is plated) and after consumption. The researcher will use the photographs to estimate the percentage consumed. Participants will also be asked whether they shared any of their meal with someone else, and if so, to estimate the percentage shared. Energy and nutrients consumed will then be calculated by multiplying the calorie/nutrient content of each item by the percentage that was consumed (considering any sharing), and adding this together across all items to calculate total energy/nutrients consumed. All percentage estimates will be independently verified by a second researcher.

Pre-meal energy and nutrient intake

In the follow-up survey, participants will complete a dietary recall questionnaire (Intake24). They will be asked to provide as much detail as possible on what they ate for breakfast and lunch on the same day that they consume their Tesco order. We anticipate that participants may compensate for their order by consuming less at prior mealtimes (or, conversely, they may consume less of their order is they consumed more at prior mealtimes). Intake24 will then produce estimates for total energy, saturated fat, salt, and sugar consumed.

Label awareness

All participants will be asked "Did you notice any nutrition labels on the items when making your initial food choices?" (yes/no). If \[yes\], "What did the label(s) look like?" Response options (label name and an image of the label): Nutrient warnings, Traffic lights, NutriScore, Keyhole, Health Star Rating.

Price awareness

All participants will be asked "Did you think about the price of the items when making your initial food choices?" (yes/no).

Policy support

All participants will be asked (i) "If the UK Government introduced a policy that required all packaged foods high in calories, saturated fat, salt, and/or sugar to display nutrient warning labels, how would you feel?", (ii) "If the UK Government introduced a policy that required all packaged foods high in calories, saturated fat, salt, and/or sugar to be taxed so that they are 20% more expensive, how would you feel?" and (iii) "If the UK Government introduced a policy that required all packaged foods high in calories, saturated fat, salt, and/or sugar to be taxed so that they are 10% more expensive, how would you feel?" Likert scale ranging from 1-5 anchored by "Strongly oppose" and "Strongly support". The order of presentation for these questions will be randomised, and only one question will be displayed at a time.