Do nudges need a regulatory push? Comparing the effectiveness and implementation of exemplar nudge (size-based) and non-nudge (price-based) dietary interventions

Changing behaviour across populations is key to improving population health and achieving net zero by 2050, including changing diets. We examine the extent to which nudges, with the potential to contribute to such change, are being implemented alongside traditional approaches. We compare the effectiveness and extent of implementation into policy of two interventions to improve diets: size-based interventions that alter portion, package or tableware size, commonly considered a nudge ; and, price-based interventions, including food-item taxes, not considered a nudge . We conducted four rapid reviews: two for systematic reviews with meta-analyses aimed to determine the effectiveness of size-based and price-based interventions, respectivel y ; and two for reports to estimate the extent to which size-based and price-based interventions have been implemented in health or environment policies of governments, public authorities, or private sector organisations, at national or sub-national levels. Both sets of interventions were consistently found in research studies to be effective at reducing consumption and purchasing of unhealthy products, but price-based interventions have been implemented in policies far more often than size-based ones. At least 118 countries have implemented taxes on sugar sweetened beverages (SSBs), and 42 countries have implemented taxes on unhealthy foods. In contrast, we identified 20 reports of size-based interventions implemented at sub-national level, of which only one involved regulation. Explaining and reversing the lack of implementation of size-based interventions and other effective nudges merits prioritisation to help realise global ambitions to improve population health and achieve net zero by 2050. • Nudges could change behaviour but how likely are they to be implemented at the scale needed to improve population health? • We compared the effectiveness and implementation of size-based (nudge) with price-based (non-nudge) dietary interventions. • Both interventions reduced unhealthy product consumption, but price-based ones were far more likely to be implemented. • Realising the potential of nudges requires implementation through regulation. • Explaining and reversing the negligible implementation of nudges should be prioritised by researchers and policy-makers.