Optimising Swaps to Reduce the Salt Content of Food Purchases in a Virtual Online Supermarket: A Randomised Controlled Trial

Background: Offering 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.

Objectives: To 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.

Methods: In 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.

Results: 947 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.

Conclusions: Offering 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 Registration: ISRCTN, ISRCTN91306993. Registered 5th February 2018 - retrospectively registered. https://www.isrctn.com/ISRCTN91306993.