Optimising swaps to reduce the salt content of food purchases in a virtual online supermarket: A randomised controlled trial

Abstract

BackgroundOffering consumers the opportunity to swap to lower-salt foods while shopping has potential to reduce salt intake. Offering a wider range of alternatives which are much lower in salt could increase the magnitude of salt reduction gained but may interfere with consumers’ engagement and willingness to accept swaps.ObjectivesTo compare the salt reduction from offering swaps to a similar product but with minimally less salt to offering swaps with a substantial salt reduction including a range of alternative foods.MethodsIn an experimental, randomised trial conducted in a virtual online supermarket, participants with high blood pressure were asked to buy 12 items of food. One group was offered similar alternatives with 5–20% less salt (LS swaps); and the other group was offered these LS swaps and alternatives with >20% less salt (MLS swaps). The primary outcome was the change in salt density of the shopping basket (g/100g) from initially selected items, to the final items chosen.Results947 participants completed the task and were included in the analysis. There was a significant reduction in salt content of the final selected shopping basket in both groups; with a significantly greater reduction in the group offered LS + MLS swaps (−0.09g/100g, 95% C.I. −0.10, −0.07; p < 0.001). The proportion of swaps accepted was the same in both groups and the mean salt reduction per swap accepted in the group offered LS + MLS swaps was more than double that of the group offered LS swaps alone. 30% of MLS swaps accepted were from a different food subcategory.ConclusionsOffering alternative products with a large reduction in salt, including potentially dissimilar products, does not decrease acceptability and leads to significantly greater reductions in the salt content of the shopping basket.Trial registrationISRCTN, ISRCTN91306993. Registered 5th February 2018 – retrospectively registered. https://www.isrctn.com/ISRCTN91306993.

Effects of Labelling and Increasing the Proportion of Lower-Energy Density Products on Online Food Shopping: A Randomised Control Trial in High- and Low-Socioeconomic Position Participants

“…There are limitations to the present research. Although the online supermarket shopping environment has been used in previous research [8][9][10], participants made hypothetical product selections and did not spend money. There is some evidence that hypothetical purchasing tasks administered virtually relate to purchasing behaviour in the real world [34,35], but replicating the present findings in real-world settings would be informative.…”

“…The website is a research platform that recreates an online supermarket designed to support experiments into health behaviour and nudging. The site has all of the essential features of a normal online supermarket: browse and search for products, add products to the basket and check out, and has been used in previous research work [8][9][10]. It contains a grocery product range (FoodDB database [19]) including products names and images, department, aisle and shelf of the products, product size and nutritional information (energy, fat, saturated fat, carbohydrates, sugar, salt, fibre and protein).…”

“…Participants were asked to complete an online shopping task using a pre-determined shopping list of 10 items, as in previous studies using an online experimental supermarket [8][9][10]. When entering the website, participants were instructed to buy all the items on the list, selecting foods that they and their household would be likely to eat (see Supplementary File 1 for complete instructions).…”

“…were excluded. We analysed data from participants who bought at least 5 items out of 10 from the shopping list, and if participants bought more than the 10 items requested, as in previous research, we included all items bought [8][9][10].…”

“…Recent reports suggest that the number of people ordering food from supermarkets online has grown rapidly [6,7]. A small number of studies testing interventions in online supermarkets have shown that offering shoppers healthier product "swaps" and positioning healthier food products more prominently can improve the nutritional quality of food purchases [8][9][10].…”