Background Obesity and type 2 diabetes mellitus (T2DM) are leading causes of poor health.

Increasing evidence points to an effectiveness hierarchy in prevention from upstream policies, which shape external factors, to downstream interventions, which place responsibility for change on individuals.

This study used recent empirical evidence from two national programmes using these different approaches; the English NHS Diabetes Prevention Programme (NHSDPP), an individual lifestyle intervention to prevent T2DM, and the UK Soft Drinks Industry Levy (UKSDIL), a tax to producers aimed to reduce sugar concentration, to compare future health, cost-effectiveness and equity outcomes.

Methods We used comparative risk assessment using WorkHORSE, a validated microsimulation model programmed in R v4.04.

Our baseline scenario models current and future exposures and mortality population trends. It models the average performance of the existing NHS screening programme. The baseline population was England, adults 40–74 years old without pre-existing conditions. The simulated period was 2019–2040.

We modelled three scenarios using the following parameters:

1) NHSDPP scenario: mean weight-loss 3.0% in 18.0% of individuals with BMI ≥ 30 kg/m2, £270 cost per participant, and attrition rate of 20%. Parameter data based on NHSDPP programme information.

2) UKSDIL scenario: 0.06% BMI reduction across the population. Equivalised BMI effect based on UKSDIL’s reported sugar reduction and meta-analysis studies of SSBs exposure and BMI changes.

3) Combined scenario.

The primary health outcome was T2DM cases prevented or postponed (CPP). We applied standard UK Treasury discount rates. Sensitivity analysis explored effects upper boundaries.

Results The NHSDPP resulted in about 7,100 (95% Uncertainty Intervals 3,600 to 10,000) CPP, net monetary benefit (NMB) of -£7M (-£640M to £600M), 50% probability of being cost-effective and 30% probability of being cost-saving. The UKSDIL and Combined scenario resulted in approximately 11,000 (7,700 to 15,000) CPP, £430M (-£140M to £1,100M) NMB, 90% probability of being cost-effective and cost-saving; and 18,000 (14,000 to 22,000) CPP, £410M (-£210M to £1,000M) NMB, and above 80% probability of being cost-effective and cost-saving, respectively. No scenario reduced socioeconomic health inequalities. Sensitivity analysis gave broadly similar results.

Conclusion Our estimates are more conservative than estimates from other similar, separate studies. Our study adds to the body of evidence supporting the effectiveness hierarchy of upstream over downstream policies. Whilst immediate transition to upstream policies is politically challenging, governments must balance both approaches.