Dr Oliver Mytton and Dr Mike Rayner of the Department of Public Health at Oxford are the lead authors of paper in the BMJ summarising the evidence on health-related food taxes.
The researchers conclude that taxes on unhealthy foods do have the potential to improve health. They suggest that a taxation level of around 20% (equivalent to VAT) could have a meaningful reduction in disease within populations.
However, they say the evidence base needs strengthening to better predict the wider effects of introducing some of these taxes – such as 'fat taxes' or 'junk food taxes' – and understand what foods consumers might switch to.
Beyond their analysis in the BMJ of the existing evidence, Dr Mytton and Dr Rayner believe that the urgency of the health problems related to poor diets in the UK demands action now.
They believe a tax on sugary drinks would be a safe and reliable option to improve health.
Dr Rayner said: 'Obesity has rocketed recently and if anything our diet is getting worse. We need to take steps to tackle this problem as a nation. It's affecting our health and it’s affecting our wallets through the increased burden on the NHS and the taxpayer.
'David Cameron said that he wanted to look at fat taxes last October. He should now commission an independent review of the existing evidence that looks at the options for taxing unhealthy foods.'
The Oxford team argue that government intervention such as taxation can be justified when the market fails to provide the 'optimum' good for society's well-being, as with the duties on alcohol and tobacco, for example.
A tax on sugary drinks is one measure that is a sure, safe bet that would change how many calories people consume across the nation and have a significant effect on obesity levels.
Dr Mike Rayner
'It is basic economic theory that raising the price will change consumption, and we already use the taxation system in this way to influence behaviour,' explained Dr Rayner. 'We have taxes on unhealthy goods such as tobacco and alcohol. And we don't have taxes on books as they can be seen as a public good to be encouraged.'
He added: 'There would be benefits for the healthcare system too. It would save taxpayers' money through reduced NHS costs as well as combat diet-related disease such as obesity and heart disease.
'It is also likely that a tax on unhealthy foods would act as an incentive to encourage manufacturers to change what goes into their products and make them healthier over time.'
A tax on sugary drinks is not going to cure obesity by itself, Dr Rayner is careful to state. 'There is no single solution: we need an environment conducive for good health. We need a comprehensive strategy to deal with the affordability, the availability and the promotion of unhealthy foods.'
VAT is already applied to some foods and drinks in this country, but it is done inconsistently – as the recent pasty tax debate revealed. 'VAT should be totally reformed in line with health goals,' said Dr Rayner.
New taxes introduced in Denmark (on saturated fats) and France (on sweetened drinks) will provide the opportunity to evaluate the effectiveness of such measures in the coming years.
Taxes can have untoward or unexpected effects, and it is possible that a tax on saturated fats, like that introduced in Denmark, could be counter-productive, suggests Dr Rayner.
In avoiding some foods high in saturated fat, people could replace them with foods high in carbohydrates – food that also tends to be high in salt. The overall effect on health might be negative.
That is why Dr Rayner believes a tax on sugary soft drinks is the best option. Even if people moved to diet drinks instead, it would still be beneficial for health.
'A tax on sugary drinks is one measure that is a sure, safe bet that would change how many calories people consume across the nation and have a significant effect on obesity levels,' said Dr Rayner.