Celebrity chef Jamie Oliver and health experts have been asked to help the Government in tackling the problem of obesity in primary school children.
David Cameron said it was "disturbing" that 10% of children are obese when they begin primary school but the figure rises to 20% by the time they leave.
The Prime Minister said obesity was an "enormous health challenge" for the country with a "vast" cost to the NHS.
Mr Cameron said: "I think the point I'd make when you look at the most disturbing figures it's the fact that 10% of children go into primary school obese, but 20% are coming out of primary school obese and so it's this primary school period where we really can do better."
He said he had "tasked the Department of Health, Department for Education, working with Jamie Oliver and others, to look at this period and think 'well, what can we do better?'"
The Government is set to produce a childhood obesity strategy in the autumn and experts including OIiver were recently invited to Downing Street for a one-off session so the Prime Minister could hear their views about the challenge.
A Government official said Mr Cameron had the chance to talk to Oliver about the issue and the Prime Minister wants experts to come forward with ideas to tackle the problem.
Chief Medical Officer Dame Sally Davies and leading economists were also at the Downing Street session, with the Prime Minister keen to get different perspectives on the issue.
Mr Cameron said: "Of course we want to reduce rates of obesity across the country, this is an enormous health challenge. If you look at the cost to the health service, it's absolutely vast and there's no doubt that the next phase of improving the health of the nation, preventative health and better health is going to be absolutely key.
"But I think the real focus should be how we tackle that 10% to 20% problem in primary schools. So it's a combination of diet, exercise and how we talk to children and parents about this vital issue."