WASHINGTON - Though close to a billion people remain undernourished worldwide, one in three U.S. children are overweight - a problem that First Lady Michelle Obama has made her priority over the first two years of her husband's administration.

McDonald's Happy Meals sell and fewer kids are getting the exercise they need. Though close to a billion people remain undernourished worldwide, one in three U.S. children are overweight - a problem that First Lady Michelle Obama has made her priority over the first two years of her husband's administration. (Photo: Reuters) This rate of overweight or obese U.S. children has tripled in the past 30 years and is now becoming a broader problem for wealthy countries more generally, officials say.

Health and obesity issues, says Sam Kass, assistant chef at the White House and senior policy adviser for the Obama's Healthy Food Initiatives, are now an international challenge.

"It's not just a challenge for the United States, although we've been dealing with it for quite some time. But you see rates going up all over the world and that's going to be an increasing challenge that we're going to have to come together to work on - to try to make sure that all of the world's citizens are getting the food that they need to nourish themselves," he told a group of reporters Tuesday.

Obesity in children can lead to emotional as well as dangerous physical conditions including diabetes, heart disease, high blood pressure or even cancer. And, for someone used to the amenities of modern life, obesity can have multiple causes - lack of exercise, too many high-sugar or high-salt snacks, unhealthy school lunches, etc.

With that in mind, Obama's approach has been to take on the problem from multiple angles.

In February, her office launched a campaign called Let's Move to facilitate partnerships between U.S. states, business and non-profit organisations toward the goal of solving the challenge of childhood obesity within a generation.

What does that mean exactly? Twenty years from now, says Robin Schepper, executive director of Let's Move, they hope to have the childhood obesity rate in the U.S. down from its current level of 30 percent of kids to five percent - the level it was at in 1972.

Reaching that goal will require a multipronged approach.

Schepper says that when she was growing up in New York City in the 1960s and 1970s, 70 percent of kids walked or bicycled to school, while 30 percent rode in cars. "It is the reverse now, so we can't just say it's the food&You can have the best food, eating fruits and vegetables at every meal, but if you don't have sidewalks in your neighbourhood and you're not being active, that's a problem."

"The realisation we came to very early on was there is no magic bullet. There is no one thing we can do to solve this problem. This is the culmination of a lot of issues in modern society," says Kass. "If we're missing major pieces of a kid's life - the breakfast they eat or if they're not getting physical activity in schools or when they get home - we're not going to solve this problem."

To that end, education, urban planning and a wealth of other considerations in addition to health - Schepper says 13 different federal agencies worked on a past report on the childhood obesity issue - come into play when figuring out how to combat the problem.

The most visible action the first lady has taken was in the early days of Obama administration, when she planted an vegetable garden on the White House grounds which has been credited for increasing the U.S. public's interest in growing their own fruits and vegetables and has been used as a way to raise awareness of the importance of eating healthy.

The fall harvest of that garden took place just last week and yielded about 400 pounds of food. Kass says that the 1,500-square-foot garden has produced about 2,000 pounds of produce in its one and a half years - "a lot for a small garden", he says.

A portion of the produce is used in the White House kitchen, while the rest is donated to help feed the homeless in Washington.

In addition to these programmes, the White House has called for 400 million dollars to be invested in expanding access to fresh, healthy food in underserved, traditionally poor neighbourhoods - sometimes called "food deserts", where convenience stores and fast food restaurants are often the only food options nearby.

Another initiative - reauthorisation of the Child Nutrition Act, which would provide funding for school meals programmes - has yet to be approved by Congress, though might be following next week's U.S. elections.

But some critics see the White House's efforts as more symbolic than anything else. Ultimately, they feel, the initiatives lack the amount of money that will be needed in order to do things like make school lunches healthier. Some also want more fundamental changes to a U.S. food system that often makes unhealthy foods easier to obtain, through measures like subsidies for the production of corn syrup and other products.

"Only being nine months into it," says Kass, "I think we've made substantial progress, but we obviously have a long way to go."