More than 30 obese patients were referred for weight-loss surgery last year at an estimated cost of £225,000 to taxpayers.
Figures recorded by the Health and Social Care Information Centre (HSCIC) show that 33 people were referred for surgery in St Helens 2012/13 - the second highest number per person in the North West with only Blackpool seeing higher numbers.
Depending on the complexity of the procedure and the care required after surgery, NHS England says bariatric surgery costs can vary between £3,000 and £11,505.
Gastric band surgery is cheaper than gastric bypass surgery, which is a more complicated and risky operation.
Guidelines recommend that bariatric surgery be offered to the morbidly obese and those who are not quite morbidly obese but already have other problems, such as heart disease and high blood pressure.
Although no surgery is carried out in the borough, St Helens NHS services still foot the bill.
There are no figures available as to how many patients have been referred during 2013/14.
The news comes as it was revealed by the National Bariatric Surgery Registry that nearly 40 per cent of under-25s who have weight-loss surgery in the UK are classified as super-obese.
Surgeons say this is evidence of “a clear failure of strategies to prevent weight gain in young people”.
Overall, more patients are having weight-loss surgery and, on average, they are getting more obese and more ill by the time of surgery.
A leading bariatric surgeon said severe obesity threatens to bankrupt the NHS.
There were more than 18,000 weight-loss operations in 137 UK hospitals between 2010 and 2013.
The operations were made up of 9,526 gastric bypass procedures, 4,705 gastric band operations and 3,797 sleeve gastrectomy operations.