• Wales’ real obesity rate has been hidden by data collection approach
• Analysis finds over a third of Welsh adults are obese, rising to 34% from official figure of 26% - making it highest rate of all UK nations
• Biggest underestimation is among over 55 year olds, potentially meaning health service provision isn’t being targeted at right people and highlighting need for action on data and obesity policy

Wales may have the highest obesity rate of the four UK nations, according to new analysis by the innovation charity Nesta.

Unlike the other three nations, official government statistics for adult obesity in Wales are calculated from entirely self-reported data. This differs from England and Scotland, where the obesity rates are calculated from self-reported data but adjusted to account for people making errors in their self-reported data. The obesity rate in Northern Ireland is based on height and weight data taken by professionals.

Previous studies from several countries have shown that people typically underestimate their weight and overestimate their height, when asked to self-report, resulting in underestimation of their body mass index (BMI).

By not adjusting their obesity rate to account for these issues with the data, the Welsh Government is significantly underestimating Wales’ official obesity rate.

New analysis by Nesta suggests that when the most recent year of self-reported data from 2022-2023 is adjusted to correct for under-reporting, the rate of adult obesity in Wales rises from just over a quarter (26%) to a third (34%). This could mean more than 200,000 additional adults in Wales are obese than previously recorded.

The analysis also indicates that adult obesity rates are higher in Wales than in England (26%), Scotland (29%) and Northern Ireland (27%).

Adjusting the adult obesity rate in Wales from 26% to 34% aligns with obesity rates amongst children in Wales - which are based on professional measurements - and which are considerably higher than in both England and Scotland.

Adjusting to account for the self-reporting of height and weight data reveals an especially large discrepancy for people over 55 years olds. The obesity rate was found to be 10 percentage points higher for those 55-64 years, 12 points higher for those 65-74 years and 11 points higher for those over 75 years, compared to the uncorrected figures. This suggests that in fact those in the 55-64 years age group are at the highest risk of obesity, rather than the 45-54 year age group as unadjusted figures would suggest. Recent Office for National Statistics (ONS) data reveals that people aged 55 and over are more likely to have health conditions and so the higher obesity rates could suggest a greater impact on health services than previously understood.

Under-reporting also differs by gender. While both men and women under-report their weight and over-report their heights, men tend to over-report their height more than women and women tend to under-report their weight more than men, according to Health Survey for England data.

As the new First Minister of Wales and former Minister for Health & Social Services, Vaughan Gething is reaching a month in post, Nesta’s analysis reveals the need for a new approach to obesity rate data in Wales so that service provision can be better targeted.

Nesta is highlighting that adjusting for the underestimation of obesity data would provide the Welsh Government with better insight to focus its resources on obesity prevention through a range of measures, including backing healthiness targets for large grocery retailers.

Jonathan Bone, mission manager of healthy life at Nesta Cymru and author of the research, said:

“Obesity is a serious public health issue in Wales, something that the Welsh Government has shown an admirable commitment to tackling previously, such as through restrictions on the promotion of high fat, salt and sugar products. But we are concerned that Wales’ official figures on obesity are not painting an accurate picture.

“Our analysis shows that Wales could be the nation with the highest obesity rate in the UK, when you correct for the use of self-reporting, because of the tendency for people to over report their height and under report their weight.

“The new First Minister has previously outlined his concerns about the high levels of childhood obesity in Wales, in his role as Minister for Health & Social Services. He should now look to make tackling obesity in Wales a key focus of his administration, and work with the other nations on developing UK-wide innovative approaches.

“To make good decisions on public health, you need good data. Having consistent reporting of public health data is important and the Welsh Government’s current approach means that they could be underestimating the impact of obesity, including for people aged over 55. Accounting for self-reporting, including retrospectively, could improve the targeting of public health interventions and make it easier to compare data both over time and between the UK nations.”

Hugo Harper, director of healthy life at Nesta, said:

“Obesity is a major public health issue across the UK. It increases the risk of preventable diseases, including type 2 diabetes, cardiovascular disease and some cancers. Its health effects also cost the NHS around £19 billion a year.

“Obesity rates aren’t on the rise because people have less willpower than they used to - what is sold and marketed to us has changed, making it harder to be healthy. It should be easier and more affordable to eat more healthily and a good start is where most of us buy our food shopping - the UK’s 11 largest food retailers.

“The Welsh Government could take the lead on this by supporting our proposal to set mandatory health targets for the largest UK retailers to improve the healthiness of the average basket sold in store or online in Wales.”

Nesta’s proposal for setting mandatory healthiness targets for large retailers would need to be implemented through primary legislation in the UK parliament and replicated in devolved nation legislatures, where health is a devolved matter, such as the Senedd in Wales.

Notes to editors

1. To correct for the discrepancy in how obesity prevalence has previously been reported across the UK nations, Nesta applied the same prediction equations used in England and Scotland to correct for bias in self-reported height and weight data from the National Survey for Wales 2022-2023. These prediction equations were developed by comparing how people reported their height and weight with what was actually measured by interviewers as part of Health Survey for England (HSE) data between 2011 - 2016.
2. Adult obesity rates for England of 26%, Scotland of 29% and Northern Ireland of 27% are based on the latest available data for these nations, from 2021-22 for England and Scotland, and 2019-2020 for Northern Ireland.
3. In England and Scotland, height and weight data was formerly taken by professionals and since 2020 has been self-reported but adjusted to approximate professionally measured data.
4. In February, Nesta published its proposal Targeting the health of the nation on setting mandatory healthiness targets for the 11 largest grocery retailers in Great Britain. Retailers would be encouraged to improve the healthiness of their offer by increasing the overall nutritional quality, as measured by a nutrient profile score. This would set the outcome but give retailers the flexibility to choose how they meet the target. Nesta’s modelling shows that this policy would help 4 million people across Great Britain move to a healthier weight, reduce obesity in Britain by around 23% after three years - and save up to £20 billion per year in NHS and other health costs. This policy would require legislation to be implemented across Great Britain, including the UK Government, the Scottish Government and the Welsh Government.
5. For more information on the analysis or to speak to one of the experts involved, please contact Kieran Lowe, Media Manager, on 020 7438 2576 or [email protected], or for Welsh media and Welsh-language media, please contact Elin Price, Campaigns and Communications Manager, on 07779 000329 or at [email protected]. Spokespeople are available for broadcast interviews.

About Nesta

We are Nesta, the UK's innovation agency for social good. We design, test and scale solutions to society's biggest problems. Our three missions are to give every child a fair start, help people live healthy lives, and create a sustainable future where the economy works for both people and the planet.

For over 20 years, we have worked to support, encourage and inspire innovation. We work in three roles: as an innovation partner working with frontline organisations to design and test new solutions, as a venture builder supporting new and early stage businesses, and as a system shaper creating the conditions for innovation.

Harnessing the rigour of science and the creativity of design, we work relentlessly to change millions of lives for the better. Find out more at nesta.org.uk