Public attitudes towards sugar, junk food and unhealthy food adverts aimed at children must change, according to a top NHS chief.
Simon Stevens, chief executive of NHS England, also said childhood obesity was a real "threat" to the country's long-term health just days after a report by MPs called on the Government to introduce a sugar tax.
Addressing the Chief Nursing Officer for England's annual conference today, Mr Stevens said the NHS had a "crucially important" role in helping lead a national debate on the issue.
He said: "I think as NHS leaders, by standing up and being counted on these topics we can help change the tide of opinion in this country.
"We have to take a more assertive stance particularly on junk food, advertising and marketing of food aimed at children and sugar."
On Monday, a wide-ranging report by the Commons health committee said the Government must not "take the easy option of relying on health education campaigns" and promoting exercise to solve the UK's obesity crisis.
Instead, they said something "far more ambitious" was needed, calling for Jamie Oliver-style graphic warnings on the side of fizzy drinks saying how many spoonfuls of sugar a single serving contains.
Furthermore, MPs suggested that a 20% tax on full sugar soft drinks be introduced, with all the money raised spent on preventing childhood obesity.
After the report's publication, Downing Street said Prime Minister David Cameron had made clear he did not think a tax on sugary drinks was "the right course of action".
The Government is set to publish its strategy on childhood obesity in the new year, where it will set out measures to tackle the problem.
Mr Stevens, speaking to hundreds of delegates in Birmingham, said: "The reality is we've got to help lead that national debate."
He also told NHS managers if the health service was to make its voice heard, the organisation needed to do more to ensure its own 1.4 million-strong workforce was in good shape.
Mr Stevens said: "We've got huge pressures showing up as stress, linked to workload pressure and culture.
He added: "So, if we're serious about health, the role of you as clinical leaders is contributing to the national debate and partly about improving support offered to our own nursing and front-line workforce."
Earlier this week, the health committee's report had come up with several recommendations including a ban on unhealthy food advertising before the 9pm watershed during TV programmes enjoyed by families, like X Factor.
MPs also said buy-one-get-one-free and other deals on unhealthy foods in supermarkets should also face "strong controls", with an outright ban on supermarkets placing sweets and other less healthy foods at the ends of aisles and checkouts.
The MPs' recommendations came after a row between the health committee, Health Secretary Jeremy Hunt and Public Health England (PHE) about recommendations in a PHE report suggesting a sugar tax be introduced.
PHE originally refused to publish its report proposing a sugar tax until the Government published its own strategy next year, but reversed that decision in the face of mounting pressure.
New figures last week showed a third of 10 and 11-year-olds in England are overweight or obese, although obesity among younger children is falling.
Sugar-sweetened drinks currently account for 29% of sugar intake among children aged 11 to 18, and around 16% for younger children.
Treating obesity and its consequences currently costs the NHS £5.1 billion every year.
A coalition of almost 20 groups has been formed to demand a 20% sugar tax and further action. Members include the Academy of Medical Royal Colleges, the British Heart Foundation, the British Medical Association, Cancer Research UK and the Faculty of Public Health.