Background Educational campaigns are often used to guide populations having a healthier diet. Current diets can be improved by limiting high sodium intakes, known to be the most important modifiable risk for high blood pressure. The UK launched a sodium reduction programme in 2005, consisting of educational campaigns and a reformulation strategy. The educational campaigns aimed at helping population make healthier choices towards manufactured foods, and reduce their use of table salt. The reformulation strategy gave manufacturers voluntary targets as an incentive to reduce the sodium content of their foods, and thus improve the composition of foods people can choose from. This study aims at analysing how changes in food composition and in consumer choice contributed to changes in the sodium density of foods consumed.

Methods Using food diaries from the National Diet and Nutrition Survey in 2008/09 and 2016/17, we estimated the average quantity of food products eaten by the UK population. We calculated the sodium density of all foods (excluding drinks) consumed using year-specific nutrient information from the UK Nutrient Databank. Changes in sodium density between 2008/09 and 2016/17 were decomposed into changes in consumer choice and changes in food composition (reformulation of existing products and product renewal, i.e. the difference in sodium content between foods exiting and entering the market).

Results The sodium density of solid foods was reduced by 15%. Reformulation resulted in a 13% decrease in sodium density. Categories contributing to most of the decrease were breads and meat and fish products. Product renewal led to a 3% decrease in the sodium density, mostly from the renewal of fruit- and vegetable-based products. In opposition to the effect of reformulation and product renewal, consumers switching between products led to a 1% increase in sodium density of solid foods consumed. This increase was the result of adverse choices in the sauces and condiment category (where consumers switched to products with higher sodium) and favourable choices in the meat and fish, and the grain-based products categories.

Conclusion Overall, the reduction in the sodium density of foods consumed was driven by reformulation. Besides for sauces and condiments, consumers made favourable choices towards products with lower sodium content. However, the relative contribution of changes in composition and changes in behaviour differed by category. Attitudes and food preference by product category should be considered in the design of educational campaigns.