Why not nanny people about healthy diet?
Poor diet is the leading modifiable risk factor for ill health in the UK.
That is not the grandiose claim of a nutrition evangelist - it's the verdict from the Global Burden of Disease Study.
This found that more than 12% of the burden of ill health was attributable to dietary risk factors. And if we add the risk from being overweight too, it's more than 20%.
On average in the UK, we eat too many calories, too much saturated fat, sugar and salt and too little fibre.
If people ate more healthily, more than 33,000 premature deaths could be prevented each year.
We've been talking about the problem for ages, but so far we have seen only very modest changes.
Public confusion about the messages doesn't help - witness the latest debate which pitches fat against sugar when the science tells us clearly that both are of concern.
NHS chief executive Simon Stevens has stressed the need to focus on preventing disease to ensure the future viability of the NHS - and the general economy.
But despite widespread acceptance of the mantra "prevention is better than cure", prevention remains the Cinderella of medicine.
The shift we need to make in our approach to healthcare is fundamental and it is going to take real investment in prevention now to reduce treatment costs later.
Research into effective interventions is vital to give us confidence that investment in prevention will reap the dividends in terms of improvements in health.
So what do we know now about how to change eating habits?
Most people do know that fruit and vegetables are good for you, and sweets are not.
But we are surprisingly poor at putting our knowledge of a healthy diet into practice.
Although we like to think of ourselves as rational, intelligent people who make good decisions, research shows much of our behaviour in relation to food or indeed physical activity, is not a conscious, deliberative act.
Rather, it is an automatic response, shaped by the circumstances in which we find ourselves and the environment and social cues that surround us.
If we restructure the environment, can we nudge the nation to better health?
Compromise for benefits?
But why stop there? Paternalists will argue that we could quickly make progress towards a healthier diet with more draconian policies.
Look at the success of the wartime rationing policy they argue - people were healthier and social inequalities narrowed.
But in 21st Century Britain how far are we prepared to compromise personal or commercial freedoms to benefit society at large?
This discussion is not one for the scientists alone - it's for everyone.
Condition linked to being overweight:
- Heart disease
- High blood pressure
- Some cancers (including breast and prostate)
- Snoring and sleep apnoea
- Stress, anxiety, and depression
To date, the mainstay of policy has been on increasing knowledge, and encouraging greater personal responsibility for the food we eat.
This is necessary, but it's not sufficient, we need to change the environment too so that the automatic choices we make are healthier too. We can't rely wholly on rational decision-making.
What are the options? The UK food industry is a world leader in terms of cutting fat, saturated fat, sugar and salt in products, but there is more that needs to be done so the rest are as good as the best.
But if the goal is to cut calories, a more appropriate option in many cases will be to reduce portion size - which of course cuts fat and sugar at the same time, while retaining the authentic composition and taste of foods.
Impact of promotion
We need also to tackle the promotion of foods and drink high in fat, sugar and salt, but a major challenge for public health research is to identify what action is likely to be most effective.
Take, for example, the case of the multi-buy ban on alcohol in Scotland. It sounded a good opportunity to cut alcohol consumption, but sales were virtually unaffected.
In contrast, our research shows that product placement in-store is crucial to shaping choices.
Placing alcoholic beverages at the end of shopping aisles produced the same increase in sales as a 4% price discount on beer or a 22% discount on soft drinks.
It seems plausible that we could reduce these "nudges" to overconsumption of unhealthy foods.
But the research so far is less clear that we can rely solely on nudge tactics to secure a positive shift towards healthier items.
What about food beyond the supermarket door?
Research shows there are more fast-food outlets in deprived areas, and people with the most takeaways close to home are almost twice as likely to be obese than those with the fewest outlets.
Interestingly this is one area where there does seem to be a public appetite for change, especially to protect children from excessive exposure to junk food.
We have seen some local authorities use planning law to introduce zoning policies to control the density of food outlets.
Schools, too, are using mandatory standards for food, including a complete ban on sugary drinks and confectionery.
But overall, food policy is patchy and inconsistent and there are lots we are not doing.
We know that food advertising has a powerful effect - but only restrict the content of television adverts for a small period each day.
Little attention is paid to other forms of advertising, from cartoon characters on cereal boxes to sponsorship of sport and the arts by food companies offering foods high in fat, sugar and salt.
We set standards for food in schools, but do little to control food provision in other public institutions - many hospital concourses are full of fast-food chains and vending machines.
One area where it is hard to deny the evidence case for action is tax.
Tax is an established part of alcohol and tobacco control policies and now seems to be working in some countries which have introduced health-related taxes on food.
For instance, a 10% tax on sugary drinks in Mexico led to a 10% drop in sales.
I suspect political reticence in Britain is borne out of anxiety about public opinion.
But given the scale of diet-related ill health facing us can we afford not to act?
A key assumption of modern politics is that we should be free to live as we like without being nagged.
Yet most of us choose to set rules for ourselves even if we don't often think of them as imposed rules.
So might we also accept our agents - in this case government - setting rules - laws - on our behalf if they help enact things we want to achieve but struggle to do alone?
We could, for example, frame rules which harness food promotion for public good, rather than solely commercial advantage.
I would be rather pleased if there was a rule which prevented people proffering cheap chocolate when I only wanted to buy a newspaper!
We are asking a lot of individuals if we expect them to take full and very personal responsibility for making healthier choices, while elsewhere condoning a food system that provides and promotes the less healthy.
- This is an edited version of the Oxford London Lecture: Knowledge, nudge and nanny by Prof Jebb