Who is to blame for our national weight problem? Is it the fast food outlets, the soft drinks companies, the supermarkets? Are we becoming the victims of our own easier lifestyles? Or should the blame be levelled at government inaction?
Not a week goes by without another proposed policy to beat obesity. Just this week we've had suggestions that shops should stop pushing impulse-buy junk food at checkouts and that food manufacturers should use less saturated fat in their products.
It is clear that doing nothing is not an option. Whatever the underlying causes the situation is bad and getting worse. In Britain nearly one quarter of adults are obese, with rates rising. Already, the majority of adults are classified either obese or overweight.
If we allow this to continue, we risk condemning millions of our children to a life of poor health and an early grave. The current generation of children could be the first in modern history to die younger than their parents.
So what to do? Improved labelling, banning advertising certain foods to children and a range of other government responses all have their critics. One of the most often-argued and now widely researched ideas is the imposition of a tax on 'unhealthy' foods, such as a tax on fat or sugar.
Today, new research published in the British Medical Journal, by researchers at the University of Oxford and the University of Reading (I am a co-author) highlights the effect that a tax on sugary drinks, such as non-diet cola or lemonade, would have on obesity. It shows that increasing the price of sugar-sweetened drinks by 20% would lower consumption by around 15%, cutting enough calories from the diets of 180,000 people that they would no longer be classified as obese. This sounds impressive, especially when it is recognised that it would also raise £275 million for the Treasury. This money could contribute towards the rising cost of treating obesity, and related illnesses, by the NHS.
It is not enough. 180,000 sounds like a lot of people but it only represents 1.3% of the millions of obese people in the UK. The £275m in tax may contribute to the costs of dealing with obesity, but is just a tiny fraction of the cost, which is estimated at around £7billion a year in England alone.
What is really needed is a much better understanding of why some groups decide to adopt unhealthy patterns of behaviour. High levels of fizzy drink consumption are likely to go alongside a number of other unhealthy behaviours. It's likely that those who drink lots of sugary drinks, who would benefit most from cutting back, are also likely to smoke, drink alcohol and have low levels of exercise. Such behaviours may also be associated with low levels of self-esteem.
On their own, simple economic measures aimed at tackling some dimension of an unhealthy lifestyle cannot work. What is needed is a deeper understanding of why some people make unhealthy choices while others do not. These may include poverty and lack of information or education, but they may also include cognitive psychological differences. Some people, from all backgrounds, seem to have a tendency to make hedonistic choices that ignore future effects.
Only by gaining a deeper understanding of why people are living increasingly sedentary lifestyles, and making bad dietary decisions, can effective targeted policy measures can be devised to tackle obesity. These may include better education for children and their parents; comprehensive and well-funded policies to encourage active lifestyles; and re-engineering the food business to give consumers, whatever their circumstances, access to healthy choices.
Such policies are likely to cost much and have long pay-off times. Ministers will need strong evidence to warrant paying the undoubtedly high political and financial costs. Britain's slide into the obesity crisis has come as an unintended consequence of social and economic progress. But we cannot tax ourselves healthy.