Marc Vetri
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Chef Marc Vetri helps American school battle obesity

27 March 2015 Last updated at 16:04 GMT

All this week Newsround is looking at food, and how you can eat more healthily.

As part of a special programme, Newsround reporter Ricky visited the United States where obesity is a big problem.

In the USA, 1 in 3 children and almost 7 in 10 adults are overweight or obese.

It's become such a big problem that one school in Philadelphia has started trying to get kids to think a lot more about their lunch.

Philadelphia is one of the first cities in the USA to reduce the amount of obese children.

They're being helped by celebrity chef Marc Vetri - America's version of Jamie Oliver.