OBESITY is the biggest public health crisis facing the NHS.

It is a complex problem and there will be no silver bullet to fix it. Unlike the diseases of the pasts, such as tuberculosis, which could be cured with antibiotics, or the scourge of cigarettes which has been significantly reduced by measures ranging from hefty taxation to the smoking ban, obesity and the damage it causes will be much harder to reverse.

So far, no country in the world has achieved a significant or sustained reduction in its obesity rates. At best, there is some evidence that the growth may be slowing down.

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According to research presented at the 2018 European Congress on Obesity in Vienna, the percentage of adults in Scotland who are classified as morbidly obese will barely change between 2015 and 2035 with a projected increase from four to five per cent.

In comparison, the proportion of massively overweight adults in Wales is expected to almost quadruple - from 3% to 11% - and nearly triple in England, from 2.9% to 8%.

Dr Laura Webber, a co-author of the study and a member of the UK Health Forum, put the outlook for Scotland down to "stronger policy drives" north of the border to combat weight gain.

In total, 65% of Scottish adults measured in 2017 were overweight or obese - include morbid obesity. That compares to 52% in 1995, but notably most of the increase in obesity rates had already occurred by 2008.

Between 2008 and 2017, overweight and obesity rates changed little - from 63% to 65%.

A slowdown is certainly welcome, but it is not the triumph our health service really needs.

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Dr Webber said: "That morbid obesity is predicted to increase across all three countries is worrying, and it's time to consider upping bariatric surgery coupled with effective interventions to help obese and morbidly obese individuals to lose weight."

Weight-loss surgery has been shown to be a cost-effective long-term treatment, not only because it changes the physical dimensions of the stomach but because it also appears to alter misfiring hormone signals that influence appetite.

Yet rates are declining. Figures obtained by the Herald earlier this year showed that the number of bariatric surgeries carried out on NHS Scotland has fallen by a fifth - from 259 in 2013/14 to 205 in 2017/18.

The question is whether changing the food environment can offer an effective alternative.

One criticism is that restricting price promotions will disproportionately affect the poorest. It is impossible to separate obesity from deprivation.

One in three adults living in Scotland's most deprived communities is obese, compared to one in five in the most affluent postcodes.

In its submission to the Scottish Government's consultation, BMA Scotland said: "Increasing food prices have in some cases led to people choosing cheaper food products that are often less healthy.

"Finding ways to ensure that healthy options are also more affordable than unhealthy alternatives can help to change people’s behaviours."

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Of course, pleasure as well as price influences shoppers and, with the best will in the world, making a six-pack of apples cheaper than a six-pack of chocolate biscuits is unlikely to make the fruit bag more appealing to someone seeking a quick endorphin hit.

Nonetheless, there is evidence that a price-based approach can work.

Professor Peter Morgan, of Aberdeen University's Rowett Institute, pointed to studies showing that subsidising healthy foods can change behaviour.

He said: "These demonstrate that both subsidies (price decrease) and taxation (price increase) significantly alter dietary consumption of targeted food items and contribute to weight control through restricting calorie intake.

"This work confirms other research which suggests that price reduction policy to reduce the cost of healthy foods is more effective on food choice than price increases (taxation)."

He said foods high in sugar and saturated fat should be automatically excluded price promotions.

The push to change the food environment through legislation is also a significant pivot away from the narrative of personal responsibility that has dominated the obesity debate for decades.

It is no coincidence that major food and drinks brands from Cadbury to Coca Cola have rushed to sponsor major sporting events.

Professor Mike Lean, an expert in human nutrition at Glasgow University, said it was vital that any obesity strategy makes clear that exercise is for health not weight loss.

"It is most important to state clearly that physical activity does not contribute usefully to weight loss, to help people already obese. The amount of physical activity required to prevent obesity and to maintain loss weight is a very great deal more than is now normal in Scotland. The amount associated with weight loss maintenance is >15,000 steps every day.

"This is normal for people who go through childhood and on to adulthood as serious sports-people, but even they have difficulty sustaining it."

Banning multi-buy deals on junk food will not be easy - expect legal wrangles over what constitute 'junk food', and 'promotion' for a start. But Scotland is already one of the fattest countries in the world and if we are serious about reversing obesity, we need a new approach.