It is a long way from an Essex pub: the celebrity-chef- turned-food-campaigner Jamie Oliver is picking up a prestigious Harvard award for his work to combat childhood obesity.

Jamie Oliver celebrates Food Revolution Day in New York (getty)

For the chef who worked his way up from an apprenticeship, not a university degree, an honour from one of the world's top universities. Jamie Oliver has been awarded this year's Healthy Cup award by the Harvard School of Public Health, with a sold-out lecture and reception in Boston.

The school's dean, Julio Frank, called Oliver a "pioneer in health communication, bringing home the seriousness of the childhood obesity epidemic to an audience of millions." And Oliver himself acknowledged the power of television to magnify his message and inspire people to change their lives. "I will continue to make programmes, and speak up about important food issues to rally the public," he said.

From a junior chef at London's foodie destination, the River Cafe, Jamie Oliver was soon singled out as a natural television star, and he has not stopped since, creating a multi-million pound empire: his latest series, on British food, screened on Channel 4 last year. But for Oliver, celebrity and cooking was about so much more than a bunch of recipe books.

If you don't know what stuff is or where to get it or what to do with it, then you haven't got choice. Jamie Oliver

First there was his restaurant group, Fifteen, which took on young people with few advantages in life and trained them to be chefs. Then, with children of his own, he turned his focus to the dire state of school dinners, with a passionate drive to improve standards and replace junk food with proper, nutritious meals.

From chef to campaigner

For the first time, here was a chef who took on politicians face to face, and demanded action. It made for riveting television, of course, but more importantly, turned the stuff on children's everyday lunch trays into a national debate.

Jamie Oliver's effort to replicate his campaign in America has undoubtedly won him respect, like the Harvard award, but just as many detractors, who resented the fact that an Englishman was criticising their diets and telling them what to eat. When he tried to win round school officials in Los Angeles, they more or less shut him out.

Nonetheless, his Jamie Oliver Food Foundation is determined to continue the work: taking his campaign against pink slime and flavoured milk across America and around the world. The charity declared 19 May Food Revolution Day, with events in 360 cities, in 43 different countries. Oliver, who was in the United States to mark the day, said it was all about empowering local people to bring food education back into schools, workplaces and communities.

Fighting the junk

He told the Boston Globe that teaching children and adults about good food was paramount: "If you don't know what stuff is or where to get it or what to do with it, then you haven't got choice. You just start buying into the vicious circle of junk, junk, junk."

Los Angeles based cook Marina Ivlev said Oliver had been her inspiration. "When he came out with this campaign of people not understanding what they're eating, and impacting their long term health, that really touched a place in my heart." She is now helping young women in her local area to come together to cook fresh meals from scratch.

Not that Jamie Oliver's British battle over school dinners is over yet: he is currently battling the Education Secretary Michael Gove over school food policies. This week, he declared himself so frustrated trying to change governments' attitudes, that he is giving up on politics and turning to business to pioneer change instead.

Feeding their conscience

But the idea of a chef turned philanthropist or even political campaigner is taking hold. In the United States, a group of celebrity cooking stars have joined together in the Chefs Make Change coalition to raise money for their chosen causes, from supporting farmers and struggling farmers to tackling world hunger.

Here, top chefs have proved just as willing to give up their time and energy for the greater good, even if not quite on Jamie's global scale: haute cuisine, no longer simply the decadant preserve of the haute bourgeousie. James Knappett and Sandia Chang, who have between them worked for some of the world's most famous restaurants, recently laid on a charity dinner at the home of food critics Nicole and David Williams.

Suppliers and sponsors rallied round to help with everything from the place settings to the champagne: two seats at the dinner were auctioned off for more than a thousand pounds apiece, and the event managed to raise more than five thousand pounds for the Manna Society, a south London charity which helps the homeless.

Helping hands

Shortly after the dinner, the Williams received a letter from an anonymous chef who told them he had found himself homeless a few years ago, but with help, he had slowly managed to put his life back together. "Today I stand with a determination more than ever to succeed, and with your help, many more people will have this chance," he wrote.

Another group of leading chefs, including two Michelin star winners, are putting together a special dinner later this year to raise money for CALM, a group set up to help people struggling with depression. They too are donating their services for free, and pulling in favours to get food and drinks donated.

Rick Bayliss, a Chicago-based TV cook who is part of the Chefs for Change initiative, believes that those in the culinary industry are natural philanthropists. They are passionate about hospitality, he says, which is fundamentally about giving, and taking care of people. Charity? That is just the logical next step, one menu at a time.

Felicity Spector writes about US affairs for Channel 4 News