Participant characteristics
Among the sixty-five randomised participants in the analytic sample, participants were predominantly female (85 %), college graduates (70 %) and white (92 %). Annual household income varied, with 20 % below $50 000 USD, 47 % between $50 000 and$74 999 USD, 28 % above $100 000 USD and 5 % choosing not to say. Thirty-one percentage of participants reported having at least one child under 18 in the household and 75 % had at least one other adult in the home for an average household size of 2·5 people ± 1·3. Participants’ mean age was 53·2 years old ± 10·7, and mean BMI (calculated using participants’ self-reported height and weight) was 36·5 ± 7·8. We did not ask participants if they typically grocery shopped online in the baseline questionnaire, given that doing most of one’s grocery shopping in-person at the time of screening was an inclusion criterion, but did note that three participants (5 %) submitted online grocery receipts in the Week One (baseline) receipt collection. More information about baseline food purchasing behaviour can be found in Table 
Food purchasing behaviour from baseline questionnaireValues in columns are 