Mark Tovey is the author of Obesity and the Public Purse.

Six billion pounds is the largest and most up-to-date estimate of the yearly NHS cost of treating diseases attributable to obesity, such as type II diabetes, coronary heart disease and gout. It is an inflation-adjusted version of an estimate produced in 2011 by researchers at Oxford University.

This number is used to shame people with weight issues – to make their private problems fair game in crass public debates about the deficit and government debt. But as demonstrated in Obesity and the Public Purse, the IEA’s latest report, it does not show the net effect of obesity on the Treasury’s fiscal position. In fact, the true cost to the Government is less than half that amount.

The uncomfortable reality is that we all have to die of something, and the government often saves money when people die early because they do not incur pension payments for as long or suffer from as many of the chronic illnesses of advanced age.

Around 40,000 deaths are attributable to elevated BMI (body mass index) annually in the UK, with 12 years lost on average per person. Adding up the yearly entitlements and NHS costs of a retiree and multiplying through yields a large saving: £3.6 billion, assuming that a three per cent discount rate is used to account for the fact that the foregone entitlements are spread over time.

Since the NHS is currently in the icy grip of a winter-related spike in demand, the topic of Government savings from early mortality could not be more pertinent. Every year, the public price of living longer is brought into focus as the cold weather drives a growing number of frail pensioners en masse into ailing A&E departments around the country.

To be clear, we are not celebrating fatness or premature mortality. Calculating the public finance effect of lost life years is a morbid task, but it is a necessary one, given that the relief obese people afford public services by dying early is almost never acknowledged in the health economics literature.

And getting this right really matters. Obese people constitute a vulnerable group in society, which will not be benefited by needless persecution. Indeed, fat-shaming may cause people to eat more: one study of 73 women found those exposed to vilifying material consumed three times as many kilocalories in the immediate aftermath compared with a control group.

Of course, the perpetrators of the burden-on-the-taxpayer exaggeration usually have good intentions: they are policy wonks who think they have the answer to obese people’s suffering – vending machine regulations, state-mandated changes to restaurant portion sizes, higher rates of tax on sugary drinks, etc.

But because they are pushing for political solutions, it behoves them to make the public interest argument. If they ever want to see their proposed government intervention enacted, and if they want significant media coverage for their idea, they know they must catastrophise obesity until their ‘solution’ is treated with the kind of reverence usually reserved only for plans relating to asteroid impact avoidance.

For example, the Chief Executive of the NHS has publicly claimed that obesity costs the NHS £16 billion a year. If true, this would mean that one in eight pounds spent on healthcare goes towards treating obesity-related diseases. This figure should not be taken seriously, however. It comes from taking the £10 billion cost of treating every case of Type I and Type II diabetes, and adding it to the £6 billion that is estimated to be the gross cost of obesity-related disease.

But the £6 billion figure already includes the cost of obesity-related diabetes and, even if it didn’t, there would be no justification for including every case of Type II diabetes – only some of which are caused by obesity – nor would there any justification for including the cost of Type I diabetes, which is not associated with obesity at all.

The public deserve better than shoddy guesstimates and exaggerations. Our rigorous, step-by-step estimate of the net cost of obesity on government finances shows the real figure to be less than £2.5 billion. This is not a trivial amount of money, but it is only 0.3 per cent of government spending. Despite the claims of some of the more excitable campaigners, obesity is not going to ‘bankrupt the NHS’.