Obesity and the health problems that are associated with it, are viewed as a health emergency.
The United States tops the industrialised world for obesity rates. But it seems the tide can be turned.
In the past five years, the city of Philadelphia, Pennsylvania, has seen children's obesity rates fall.
A BBC correspondent says it's due to a city programme called Get Philly Healthy.
In 2010, a health department report noted that obesity had become "a norm and a public health crisis" in the city, with 64% of adults and 57% of children aged 6-11 overweight or obese.
In north Philadelphia, 70% of children were overweight or obese.
Get Philly Healthy has disconnected deep fat fryers in every school, removed sugary-snack vending machines, built bike lanes, encouraged exercise in schools and businesses and sponsored fresh-produce fridges and fresh-fruit racks in 650 corner stores around the poorest parts of the city.
Now Philadelphia's obesity rate is falling. It is down 5% from 2006 - 2010, with the greatest declines amongst African-American boys and Hispanic girls.
One such school with a voluntary exercise programme is Issac Sheppard school in north Philadelphia, where daily exercise classes are held that last around 15 minutes.
"We tried a walking club," said head teacher, Jim Otto, "but we got shot at."
Children at the school do an indoors exercise class at least once per day, some of them twice.
"Our children want to run," Mr Otto said. "They want to play, they want to compete. But it's just not practical, it's not possible, it's not safe for them to do that.
"Our hope really,'' he said, ''is that our kids are going to want to say to their parents, you know, 'we could play this game,' or 'we could go to the park,' or 'we could walk,'" he adds.
But the BBC reports there are limits to how far the city can go. A proposed tax on sugary drinks was defeated.
And, according to city health commissioner Donald Schwarz, federal policies produce perverse and deeply harmful incentives.
He said subsidies for the corn that goes into high fructose corn syrup, a sugar substitute, have seen inflation-adjusted price of sugary snacks fall, whilst that of fruit have risen.
"This is a very long war,"said Dr Schwarz.