Background A stalling of improvement in all-cause mortality rates has been observed in the UK since the early 2010s. While evidence suggests that UK Government ‘austerity’ policies have been largely responsible, it has been proposed that increased obesity prevalence since the 1990s may also have played a part (given the association between obesity and all-cause deaths). The aim here was to quantify the potential contribution of increased levels of adult obesity to changing mortality rates in Scotland and England.

Methods We calculated population attributable fractions (PAFs) for the increase in obesity prevalence between the mid-1990s and late 2000s in relation to all-cause mortality for 35–89 year-olds in Scotland and England. We used obesity prevalence data from the Scottish Health Survey and the Health Survey for England, and previously-published hazard ratios (HRs) from a meta-analysis of 89 European studies (based on c.14 years’ follow-up). PAFs were applied to mortality data for 2017–19, enabling calculation – and comparison – of observed rates, obesity-adjusted rates (i.e. excluding deaths attributable to the obesity increase) and 1991-based projected rates (i.e. predicted rates had the stalling in improvement not occurred). All rates were European age-standardised (EASRs) and stratified by sex.

Sensitivity analyses included the use of different HRs, age groups, and base-years for projections. DAGs and other tools were used to assess likely bias.

Results The observed EASR for 35–89 year-old males in Scotland in 2017–19 was 1750.7 (95% CIs 1728.6, 1772.8). This reduced marginally to 1718.8 (1696.9, 1740.7) after exclusion of obesity related deaths, but was still notably higher than the projected EASR of 1447.1 (1426.9, 1467.3). The change in obesity therefore potentially ‘explained’ 10.5% of the difference between the observed and projected rates. For females, 13.6% of the difference could be attributed in this manner. However, the figures for England were notably higher: 20.1% for males; 35.1% for females. Sensitivity analyses and bias assessment suggested the potential for overestimation of effect size; however, the degree is difficult to quantify.

Conclusion A number of uncertainties are associated with PAF-based methodologies: thus cautious interpretation of results is required. A proportion of recent mortality changes may be associated with earlier changes in obesity prevalence. However, much larger proportions are not explained by obesity, and are therefore likely attributable to previously-articulated causes such as austerity. Policies are therefore required to both reverse the damaging effects of austerity, as well as to address the negative consequences of the well understood obesogenic environment in the UK.