Modelling ways to improve our health: what would be required to halve obesity?
Investigating the level of calorie reduction required to dramatically improve health across the UK
Nesta’s goal is to halve the prevalence of obesity by 2030. This means that we want obesity levels to return to the same level they were in the early 1990s. To do this, we wanted to calculate how many calories need to be removed from diets to achieve the necessary levels of weight loss.
The benefits of halving obesity to the economy are large. A recent study calculated that the annual cost of adult obesity to the UK is around £54bn (Frontier Economics 2022). Based on this figure, halving obesity prevalence would save around 300,000 Quality Adjusted Life Years every year (one QALY is one year of life in perfect health). Using the government’s estimate of the monetary value of a single QALY (£70,000) these QALY savings are equivalent to a monetary value of over £20 billion. The cost savings to the NHS are calculated to be around £3.25 billion per year.
We want to quantify the scale of intervention needed, in terms of calorie reductions, to reverse obesity figures in England.
The main motivation for this study has been to build a methodology upon which Nesta can use to assess the potential impact of different food environment interventions. Future directions for this work include assessing the extent to which current government interventions may contribute to achieving the target and which food environment interventions might be the most effective to ensure we meet the target.
We calculated the amount of weight people would need to lose to halve obesity rates by comparing the BMI distributions of 1991-2 to those of 2019, using the Health Survey for England (HSE) figures. The work involved first calculating for each respondent in the health survey sample a body weight target that would shift the BMI distribution back to that of 1991-92 and then working out the amount of calories that each person would need to cut to meet the target body weight using the model developed by Hall et al (2011). This model is considered the gold standard in the field and was also the basis of the Department for Health and Social Care’s CALORIE Model. We have performed all analysis separately for men and women and also for different body mass index categories and the details of this analysis can be found on the Open Science Framework.
We have found that halving obesity prevalence would require a small reduction in daily intake among people living with excess weight (excess weight is defined as having a Body Mass Index of 25 or higher). We estimated this to be 216 kcal daily on average, made up of 241 calories for men and 190 for women. This is equivalent to around an 8.5% reduction.
This sort of small, but sustained reduction across very large numbers of people points us towards population-level interventions in the food environment such as reformulating food, reducing junk food advertising and shifting price promotions towards healthier foods. We do not suggest or propose that these calorie reduction figures should be used to set individual calorie reduction targets for people.
It is important to recognise that obesity data is measured differently across the UK nations and the prevalence of obesity varies slightly. We intend to do a similar study using data from Scotland in 2023 and we are investigating the gaps in Welsh obesity data to understand what valuable analysis can be made there. Nonetheless, a broadly similar growth trend in obesity across the UK over the last 30 years suggests that a similar level of calorie reduction would be required to halve prevalence in each nation.