Systematic Review of Dietary Trans-fat Reduction Policies: Evidence for an Effectiveness Hierarchy?

Background: Non-communicable disease (NCD) prevention strategies now prioritise four major risk factors: food, tobacco, alcohol and physical activity. Dietary salt intake is on average 5g/day higher than the recommended intake leading to high blood pressure, cardiovascular disease and gastric cancer. Substantial reductions in salt intake are therefore urgently needed. However, debate continues about the most effective approaches. We therefore systematically reviewed the evidence on possible interventions to inform future prevention programmes. We hypothesised an effectiveness hierarchy whereby “upstream structural” interventions targeting populations are more powerful than “downstream, agentic” interventions targeting individuals. Methods: We searched six electronic databases using a pre-piloted search strategy focussing on the effectiveness of population interventions to reduce salt intake. Retrieved papers were screened, appraised and graded for quality independently by two researchers. Extracted data were categorised using nine stages along the agentic/structural continuum, from “downstream”: dietary counselling (individuals, worksite and communities), through media campaigns, nutrition labelling, voluntary and mandatory reformulation, to the most “upstream” regulatory and fiscal interventions. We also considered comprehensive strategies involving multiple components. Results: After screening 2464 candidate papers, 65 were included in this systematic review (46 empirical and 19 modelling studies). Quality was variable. Multi-component strategies combining downstream with upstream interventions generally achieved the biggest reductions in salt consumption across an entire population, -3g/day in Finland, -4g/day in Japan and -1.5g/day recently in the UK. Tax interventions were considered in a few modelling studies; effects were mixed and modest. Mandatory reformulation achieved reductions of at least -1.45g/day, more than food labelling or worksite interventions (each typically -1.2g/day, but with a wide range). Smaller population benefits came from interventions in schools (-0.2g/day to -0.7g/day), and even smaller ones from health education media campaigns (-0.2g/day or less). Dietary advice achieved -2g/day reductions in compliant individuals in trials (representing an estimated population reduction of approximately -1g/day). Conclusions: Comprehensive strategies involving multiple components and “upstream” population-wide policies such as mandatory reformulation, and food labelling or worksite interventions appear to be most effective in achieving population-wide reductions in salt consumption. In conclusion, this ‘effectiveness hierarchy’ might deserve greater emphasis in future NCD prevention strategies, with correspondingly less emphasis on weaker ”downstream” individually-based interventions.