Re: Potential impact on prevalence of obesity in the UK of a 20% price increase in high sugar snacks: modelling study
We thank Kevin Hall for this response. The use of static or dynamic weight loss model was raised during the review process for our paper (https://www.bmj.com/content/366/bmj.l4786/peer-review). We agree with the reviewers and Kevin Hall that, over a longer time period, the static model overestimates weight loss for the reasons he describes. Therefore, the timespan we used in our analyses stops at one year.
We do, however, stand by the point we made in response to the paper’s reviewers that, in the shorter run (the first year), the absolute differences generated by the two models are small. The prediction of weight loss by Lin et al (https://www.ncbi.nlm.nih.gov/pubmed/21940223) following a 20% price increase in SSBs shows the two models provide ‘noticeable’ differences within half a year (difference of 0.2 kg [-0.8kg vs -0.6kg]) and at one year the estimated weight loss between models differs by 0.6kg (Lin et al. do not provide confidence intervals). Similar to Lin et al, our models considered multiple sources of uncertainty arising from the use of different datasets and several estimation/modelling steps, which are reflected in the large confidence intervals around our predictions. The lower end of our reported range is similar to the 60% difference estimated by Lin et al between the two models: our predicted mean weight loss of 1.3kg at the one-year point was reported with a confidence interval ranging from 0.51kg and 2.1kg.
If we assume that estimates of weight loss are more likely to be in the lower range of our predictions, our conclusion remains intact: fiscal intervention to increase the price of sweet snacks could be more effective in the UK context than the positive effects observed around the world for taxes on SSBs. This is because price responses are similar between SSBs and sweet snacks, the difference between them being that the latter are a source of far more energy in average UK diets.
The consumption of sugary snacks (or the snack to drink ratio) is relatively high in the UK, especially when compared with other high-income countries. For example, in the UK the market size of sweet snacks is 19.3kg per kg per person in comparison to 161.3L of soft drinks. The respective figures in USA are 14.3kg and 346L (Euromonitor International, 2014). Although not providing us with the exact caloric intake and sugar consumption by food group, these simple figures highlight the need for policies targeting sugary snacks as well as sugary drinks.
Given that reformulation, the mainstay of UK public health policy to improve the nutritional quality of the diets, is proving ineffective in reducing sugar content of cakes, biscuits and confectionery (https://www.gov.uk/government/publications/sugar-reduction-report-on-fir...), other policy options to reduce consumption of sugary snacks are urgently needed.
We neither suggest nor wish to imply that a price rise on sugary snacks is the sole solution to obesity. There is no one solution and, as such, every little step counts towards the bigger goal of a fundamental shift in eating patterns towards a healthier, lower energy diet.
Pauline Scheelbeek, Laura Cornelsen, Theresa Marteau, Susan Jebb, Richard Smith
Competing interests: No competing interests