Background High salt intake is a significant cause of diet-related disease. The salt content of much of the food provided in the out-of-home food sector (OOHFS; e.g., restaurants) can be excessive, but policy options to address this are lacking. An emerging policy approach with limited evidence from randomised controlled trials (RCTs) is the use of ‘high in salt’ warning labels on restaurant menus.

Methods UK adults participated in an RCT to test the perceived message effectiveness (PME) and impact on hypothetical food choice of salt warning labels in packaged food and restaurant scenarios (Study 1). Next, the same outcomes were examined in a real-world RCT. Customers selected, consumed and purchased meals in a restaurant from menus with vs. without salt warning labels (Study 2).

Findings Study 1 (N = 2391) demonstrated that salt warning labels were perceived by consumers as being effective in discouraging high salt intake and reduced hypothetical salt selection vs. control across both packaged food (on average −0.08g [95% CI −0.12 to −0.04] per item) and restaurant (on average − 0.26g [95% CI −0.43 to −0.10] per meal) scenarios. Study 2 (N = 454) replicated findings from Study 1, for perceived effectiveness and reduced salt selection vs. control (−0.54g [95% CI −0.83 to −0.25] per meal) in a real-world restaurant setting.

Interpretation Salt warning labels on restaurant menus are a promising policy option to address excessive salt intake in the OOHFS.

Funding National Institute for Health and Care Research Oxford Health Biomedical Research Centre (NIHR203316); European Research Council (8031940).

The authors have declared no competing interest.

NCT06458270

https://osf.io/vyh2x/?view_only=9063c20d2cd14069aeb953eda4ccac27

https://osf.io/whzc8/?view_only=e97eb9ff6812457081d6d693e27bf1bd

This research was funded by National Institute for Health and Care Research Oxford Health Biomedical Research Centre (NIHR203316) and European Research Council (8031940).

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Study 1 - University of Liverpool Health and Life Sciences Research Ethics Committee (Psychology, Health and Society), reference number: 4612. Study 2 - University of Liverpool Institute of Population Health Research Ethics Committee, reference number: 11251.

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