OBJECTIVES: People living with obesity typically incur higher healthcare costs than those with healthy weight, and these costs increase with obesity severity. We estimated the impact of weight loss in a UK population on the prevalence of obesity classes and associated healthcare costs.

METHODS: The analysis considered adults aged 20–<70 years, defined according to body mass index (BMI) as having obesity class I, II or III (30–<35 kg/m², 35–<40 kg/m² or ≥40 kg/m², respectively). The estimated prevalence of each obesity class in the UK in 2033 was derived from the 2022 World Obesity Atlas, combined with 2021 Health Survey for England obesity estimates and 2019 data from the Discover electronic health record data set, which covers 2.8 million people living in North West London. The effects of 10% weight loss on the number of people in each obesity class and associated healthcare costs were estimated using the BMI distribution and costs observed in the 2019 Discover data, and scaled to the UK population.

RESULTS: Weight loss of 10% was estimated to result in a 47% reduction in the number of people with obesity in 2033, equating to 8.1 million fewer people in the UK <70 years old living with obesity (4.8, 2.0 and 1.3 million in obesity classes I, II and III, respectively). The estimated mean per-person annual cost reduction was £350 for moving from obesity class III to II, £207 for moving from obesity class II to I and £171 for moving from obesity class I to overweight. This would result in an estimated £2.5 billion annual cost saving, mostly contributed by people moving from obesity class I to overweight.

CONCLUSIONS: Our estimates of the obesity prevalence and cost reductions that could be achieved via weight loss highlight the potential impact of targeted weight management support.